BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] This invention relates to a method of driving an electrooptical display device.
[0002] Although the electrooptical display devices to which the present invention is directed
include all display devices which exhibit a capacitive property, such as a liquid
crystal, an EL, and the like, the following description will be of a display device
which uses a liquid crystal, by way of example.
2. Description of the Related Arts
[0003] Figure 2 of the accompanying drawings is a wiring diagram showing the relationship
between matrix electrodes and a drive circuit of a conventional simple matrix type
liquid crystal display device. In this diagram, symbols X1 to Xm denote segment electrode
lines; Y1 to Yn common electrode lines; 201 is a segment electrode drive circuit for
driving the segment electrode line; 202 is a common electrode drive circuit for driving
the common electrode line; 203 is a control circuit for controlling the segment electrode
drive circuit 201 and the common electrode drive circuit 202; and 204 is a drive power
supply circuit for generating a power supply voltage for driving the segment electrode
drive circuit 201 and the common electrode drive circuit 202 and generating a liquid
crystal drive voltage to be applied to the segment electrode line and to the common
electrode line through the two drive circuits 201 and 202.
[0004] A specific example system of the circuit construction are shown in Fig. 2, and Fig
3 shows only one thereof, to simplify the explanation. Therefore, although the explanation
will be given in detail on the basis of Fig. 3, the technical concept of the present
invention also can be effectively applied to the drive circuits of the other systems
shown in Fig. 2, for example.
[0005] In Fig. 3, a segment electrode drive circuit 301 comprises a logic circuit 305 for
processing the signals sent from a control circuit (not shown in the drawing) and
an output circuit 302j which selectively supplies +Vs or -Vs to the
jth (j = l, ..., m) segment electrode Xj on the basis of the instruction from the logic
circuit 305. Namely, when a transistor 303j is ON and a transistor 304j is OFF, +Vs
is applied to the segment electrode line Xj, and when the transistor 303j is OFF and
the transistor 304j is ON, -Vs is applied to the segment electrode line Xj. A state
wherein the two transistors 303j and 304j are simultaneously ON does not occur. The
substrate of these transistors 303j and 304j are connected to positive and negative
power supplies +Vd and -Vd, which are applied to the logic circuit 305, respectively
(with the proviso that |Vd| ≧ |Vs|.
[0006] Further, the common electrode drive circuit 306 comprises a logic circuit 311 for
processing the signals sent from the control circuit (not shown and an output circuit
307k which selectively supplies +Vc or -Vc or 0 to the
kth (k = l, ..., n) common electrode line Yk on the basis of the instruction of the
logic circuit 311. Namely, when a transistor 308k is ON and a transistor 309k and
a (semiconductor) switch 310k are OFF, +Vc is applied to the common electrode line
Yk, and when the transistor 308k and the switch 310k are OFF and the transistor 309k
is ON, -Vc is applied to the common electrode line Yk. While, when the switch 310k
is ON and the transistors 308k and 309k are OFF, zero (0) potential is applied to
the common electrode line Yk. A state wherein at least two of the transistors 308k
and 309k and the switch 310k are simultaneously ON does not occur. The substrate of
these transistors 308k, 309k and the substrate of the transistor that constitutes
the switch 310k are connected to the positive and negative power supplies +Ve, -Ve,
which are applied to the logic circuit 311, respectively (with the proviso that (|Vc|
≧ |Vd|).
[0007] Therefore, the difference voltage between the segment electrode drive voltage VXj
(+Vs, -Vs) and the common electrode drive voltage VYk (+Vc, 0, -Vc) is applied to
the pixel Pjk formed at the point of intersection between the segment electrode Xj
and the common electrode Yk, and there are several methods of selecting the timings
for selecting each of these voltages.
[0008] Figure 4 is a diagram showing an example of the ideal voltage waveforms to be applied
to the liquid crystal by using the circuit construction shown in Fig. 3. In this diagram,
periods T1(tl), T2(t2), ..., Tn(tn) represent those periods in which the first segment
electrode Yl, the second common electrode Y2 and the
nth common electrode Yn are selectively driven, and the period from the period T1 to
the period Tn (or from the period tl to the period tn) is one vertical scanning period.
The respective pixels are driven by the voltage applied during the selection period,
which is 1/n of one vertical scanning period, and during the non-selection period
which is l - (1/n) of one vertical scanning period. During the period T1, +Vc is applied
to the segment electrode Y1 and the 0 potential is applied to the other common electrodes.
During the period T2, -Vc is applied to the segment electrode Y2 and the 0 potential
is applied to the other common electrodes. The system which reverses the polarity
of the selective drive voltage whenever the row to be driven is selectively changed
in this manner is referred to as a "row reversion system". In the subsequent vertical
scanning period tl, ..., tn the polarity of the selective drive voltage to be applied
to each row is further reversed, and this system is referred to as a "field reversion
system". Accordingly, the system shown in Fig. 4 is referred to as a "row reversion/field
reversion system".
[0009] Furthermore, the drive voltage applied to the segment electrode is determined in
accordance with the data which is to be displayed. Assuming that the pixel portion
corresponding to the segment electrode Xa is to be displayed black throughout all
the periods, the pixel portion corresponding to the segment electrode Xb is to be
displayed white throughout all the periods, and the liquid crystal panel to be used
is normally black (which becomes more and more transparent with an increasing applied
voltage), then the voltages such as VXa and VXb shown in Fig. 4 are applied to the
respective segment electrodes. For example, a voltage VY1 - VXa is applied to the
pixel Pa1 at the point of intersection between the common electrode Y1 and the segment
electrode Xa, and the voltage waveform thereof is represented by VPa1 in Fig. 4. A
voltage such as VPbl shown in Fig. 4 is applied to the pixel Pbl formed by the common
electrode Y1 and the segment electrode Xb.
[0010] Assuming that the liquid crystal responds to the effective value of the voltage applied,
the effective value of the voltage applied to the pixel Pa1 described above during
one scanning period (hereinafter referred to as the "driving effective voltage") is
expressed by the formula (1) below and the driving effective voltage applied to the
pixel Pb1 described above is likewise given by the formula (2) below :


[0011] The difference between the formulas (1) and (2) given above appears as the difference
of the display state (dark and bright). Accordingly, the greater this difference,
the better the display, and the condition that provides the best display state is
that under which the quotient (Von/Voff) obtained by dividing the formula (2) by the
formula (1) becomes the greatest, and is given by the formula (3) below. The quotient
(Von/Voff) at this time is given by the formula (4) below:


[0012] The ratio |Vc|/|Vs| is referred to as a "driving voltage ratio" and when the driving
voltage ratio satisfies the formula (3), the ratio is referred to as an "optimum driving
voltage ratio". The values Voff and Von are determined primarily when Vc and Vs are
decided. A driving effective voltage outside this range cannot be applied in principle,
but a driving effective voltage between Von and Voff can be applied. An example of
the segment electrode driving voltage waveform in this case is represented by VXc
in Fig. 4. When much a means is employed, a liquid crystal television apparatus requiring
a gradation display can be accomplished.
[0013] When the formula (3) is employed, the value |Vs| that provides the maximum contrast
can be determined when |Vc| is set to a certain value, and the contrast drops at values
other than this |Vs| value. Nevertheless, since the waveforms much as VXa, VXb, VXc,
etc., shown in Fig. 4 represent merely the ideal state, and such an ideal state cannot
be attained in practice because dull portions (inclusive of spikes) occur in the liquid
crystal drive voltage waveform due to the influences of the parasitic resistance existing
parasitically at each portion and the capacitance of the liquid crystal. Therefore,
even if the drive voltage is set on the basis of the formula (3), to thus obtain the
maximum contrast, the contrast that theoretically should be obtained cannot be obtained
in practice. Namely, the greater the dullnees of the drive voltage waveform applied
across both ends of the liquid crystal, the greater the drop in the contrast.
[0014] Next, this dullness of the drive waveform leads to a drop in the response of the
liquid crystal. Namely, the response of the liquid crystal is increased with a greater
Von/Voff value, but if any dullness exists in the waveform, the value Von/Voff becomes
smaller and the response of the liquid crystal drops. Accordingly, when a certain
display having a quick motion is effected, an "after-image" or "image lag" phenomenon
becomes more noticeable. Furthermore, the dullness of the drive waveform results in
cross-talk, known conventionally as a critical problem, in the simple matrix type
display device. When a display such as that shown in Fig. 5(A) is effected on a liquid
crystal television receiver, for example, the practical display image becomes as shown
in Fig. 5(B). In a display device of the type wherein a display panel is divided into
upper and lower sections, to improve a driving duty ratio, and these upper and lower
display panels are driven independently of each other, the display obtained in practice
is as shown in Fig. 5(D), when an image as shown in Fig. 5(C) is to be displayed.
This is because the dull portions appear in the voltage waveform applied to the liquid
crystal, and the ideal state is not attained due to the influences of the output resistance
of the drive power supply circuit 204, the internal wiring resistance of the segment
and common electrode drive circuits 201, 202, the output resistance thereof, the connection
resistance between both drive circuits and the display panel, the resistance of the
outgoing electrode portion, and the like, as described above.
[0015] Also as described above, the dullness of the voltage waveform applied across both
ends of the liquid crystal deteriorates all the characteristics of the liquid crystal
display device, and in some cases, exerts an adverse influence such that the liquid
crystal display device can no longer be used. Counter-measures employed in the past
to solve this problem first stabilize the voltage to be given to the drive circuit
from outside and then reduce the resistance of each part as much as possible, but
it is practically difficult to make the resistance of each part zero and thus a certain
degree of resistance always remains. According1y, in many cases the conventional counter-measures
do not provide a sufficient effect
[0016] The dullness of the waveform applied across both ends of the liquid crystal deteriorates
all the characteristics of the liquid crystal display as described above. In contrast,
the present invention is directed to improve the dullness of the waveform by a novel
method, and to accomplish an ideal drive state, from all aspects. Since the cross-talk
has been primarily discussed as the principal problem resulting from the dullness
of the waveform, the explanation will be based mainly on the cross-talk problem, to
thus clearly distinguish the present invention from the prior art technique.
[0017] A typical conventional explanation of the cross-talk is shown in Fig. 6. Assuming
that all the pixels on line A display only white (or black), the column drive voltage
of the line A is reversed whenever a row scanning is carried out, and whenever this
reversion takes place, a charge/discharge to and from the liquid crystal as the capacitive
load is effected. Accordingly, the dullness occurs in the waveform even during the
non-selection period of the driving voltage VA applied to both ends of an arbitrary
one of the pixels on the line A, as represented by VA in Fig. 6. Also, assuming that
the pixels on line B pick up the display state where white and black are reversed
at every line, the column drive voltage VB of the line B retains a predetermined value,
and therefore, a charge/discharge to and from the liquid crystal during the non-selection
period is not effected, and the drive voltage applied across both ends of the arbitrary
one of the pixels on the line B becomes VB, as shown in Fig. 6. When the non-selection
periods thereof are compared, the effective value of VA is found to be smaller than
the effective value of VB, and thus the pixels which should appear at the same brightness
are dark in the line a and bright in the line B. The conventional explanation regards
this phenomenon as the cause of the cross-talk.
[0018] A proposal for an improvement based on the concept described above is disclosed,
for example, in Japanese Examined Patent Publication No. 64-4197, and this prior art
technique provides certain effects. These prior art inventions, however, are not directed
to an improvement of the dullness of the waveform itself, but are directed mainly
to making uniform the number of times of a charge/discharge that generates the dullness
of the waveform, and further, assume that the display data are binary data (black
and white). Accordingly, they are not effective for a gradation display such as a
television image.
[0019] When the display data is binary data, a switching of the drive voltage conforms with
the scanning switching timing of the common electrodes. Therefore, an adjustment can
be made so that the effective value of each column at the time of a non-selection
becomes uniform, regardless of the display pattern, by applying contrivances to the
polarity reversion period of the row drive voltage to substantially equalize the number
of times of a charge and discharge of each column at the time of a non-selection.
In the liquid crystal television receiver having a gradation, however, a switching
of the drive voltage of the segment electrodes does not always coincide with the scanning
switching timing of the common electrodes, and thus the number of times of a charge
and discharge cannot be adjusted even when the polarity of the row drive voltage is
reversed.
[0020] The inventor of the present invention carefully examined the influences of the dullness
of the waveform on the cross-talk, and found that there are some cases which cannot
be fully explained by the concept shown in Fig. 6. The inventor therefore attempted
to reproduce the liquid crystal drive state, to thereby analyze such cases. Figure
7 shows a conventional model as the basis of the explanation of Fig. 6. The basic
point in Fig. 7 is that a segment electrode, which originally should exist as a plurality
thereof, is represented by one common electrode. Namely, among a plurality of common
electrodes, a large voltage is selectively applied to only one electrode during a
certain period, and all of the others are fixed at the zero (0) potential. Therefore,
the influence of the selected common electrode is excluded by regarding it as sufficiently
small as a whole, and an absolute greater number of common electrodes that are in
the non-selection state can be collected as one electrode. Then, each segment electrode
can be regarded as an aggregate of electrodes each having a capacitance c with respective
to one common electrode which is at the zero (0) potential, and these segment electrodes
can be regarded as being switched to +Vs and -Vs by the switches S1, S2, .. each having
an output resistance ro.
[0021] The problems with this reproduction are that only the resistance component of the
segment electrodes is taken into consideration as the resistance component, and further,
only the output resistance of the switches (corresponding to the transistors 303j,
304, in Fig. 3) is handled. It is true that the output resistance of the integrated
liquid crystal driving circuit is on the order of kilo-ohms, and is by far greater
than the resistance of the resistors added, but a resistance (inclusive of the output
resistance) also exists in series in the power source line, although its value is
small, and the sum of the currents flowing through a plurality of paths are associated
with this resistance. Therefore, there may be case where this resistance cannot be
neglected.
[0022] Particularly, the power supply line resistance involved in driving the segment electrodes
is not taken into consideration in the explanation of Fig. 6, but this is believed
to be a factor that cannot be neglected when the mode of appearance of the cross-talk
in the liquid crystal television image is examined. Therefore, when the resistance
of each power supply line is added to Fig. 7, the equivalent circuit becomes as shown
in Fig. 8. In Fig. 8, a resistor RD is inserted to the +Vs power supply line, and
a resistor RS to the -Vs power supply line. For the common electrodes, a resistor
RM is added to the zero potential. This resistor RM includes the output resistance
of the common electrode drive circuit (the output resistance of the semiconductor
switch 310K in Fig. 3).
[0023] Since the cross-talk occurs when the drive waveform of the segment electrodes is
different, the case whereby a plurality of segment electrodes are divided into two
groups can be considered as an example thereof. Figure 9 shows an example where N
segment electrodes are divided into M electrodes and (N - M) electrodes. The equivalent
capacitance CB of a group (hereinafter referred to as the "B group") comprising M
electrodes is c.M, and the equivalent output resistance rB thereof is ro/M. Further,
the group (hereinafter referred to as the "A group") comprising (N - M) electrodes
has an equivalent capacitance CA of c·(N - M) and an equivalent output resistance
rA of ro/(N - M). The B group and the group A are switched to +Vs and -Vs and are
connected by the switch SB and the switch SA, respectively. The display state for
each row in each of these groups is assumed to be the same.
[0024] The results of a simulation using this example during the non-selection state are
shown in the following drawings. In the drawings, symbols SWA and SWB denote the state
of the switches SA and SB shown in Fig. 9. When SWA is at an H level, for example,
the switch SA is connected to the +Vs side, and when it is at an L level, the switch
SA is connected to the -Vs side. Symbols VDX, VSX, VMX, VA and VB represent the potentials
or potential difference at the points shown in Fig. 9. In Figs. 10 to 12, the relationship
(N - M) >> M is established, to thus provide a condition whereby the influence due
to the dullness of the waveform is noticeable, and values approximate to those of
an actual display device are selected for ro, c, RD, RS and RM. Although the value
c changes between the ON time and the OFF time in a practical liquid crystal, it is
here assumed that the value c does not change in accordance with the state, for the
purpose of simulation.
[0025] Figure 10 shows the simulation results of the case that corresponds to Fig. 6. In
Fig. 10, symbols VY1, VY2 and VY3 represent the selection timing of the common electrodes
and this diagram shows the state where the selection potential (+Vc or -Vc) is applied
to the respective common electrodes at the hatched portions while the zero (0) potential
is applied thereto during the other periods. As these merely represent the timing,
they are neglected during the simulation.
[0026] The state SWA of the switch SA described above changes to H and L whenever the selection
period of the common electrodes changes, as shown in the diagram, because the A group
described above must display only white or only black throughout the full row and
the state SWB of the switch SB is fixed to H during one vertical scanning period,
for example (to L during the next scanning period), because the B group should display
each row alternately as white and black.
[0027] The waveforms of VA and VB in Fig. 9 at this time are ideally shown by VA and VB
in Fig. 10, but in practice, these become VAX and VBX as shown in Fig. 10. Nevertheless,
although the dullness of the waveform and spikes exhibit exponential changes in practice,
they are expressed linearly for simplification. Furthermore, it is believed that the
spike for an extremely short period can be neglected when calculating the effective
value from the response of the liquid crystal, and thus this is omitted from the drawing
(this also holds true for the subsequent drawings).
[0028] When VAX, VBX are compared with Fig. 6, it can be understood that VAX exhibits a
similar tendency but VBX is apparently different. This is because VDX, VSX and VMX
change as shown in Fig. l0, due to the presence of the resistors RD, RS and RM shown
in Fig. 9. Next, this change will be explained. When the switch state SWA changes
from L to H at the time Tp, a spike-like current flows from +Vs in Fig. 9 towards
the zero (0) potential through the path ranging from the resistor RD, the switch SA,
the resistor rA, the capacitance cA and the resistor RM, and the voltage drop due
to this current changes VDX and VMX in the spike form. At this time, the current does
not flow through the resistor RS, and VSX does not change. Next, when the switch state
SWA changes from H to L at the time Tq, a spike-like current flows from the zero (0)
potential towards -Vs through the path ranging from the resistor RM, the liquid crystal
cA, the resistor rA and the resistor RS, so that VSX and VMX change. At this time,
the current does not flow through the resistor RD, and VDX does not change.
[0029] If the value N - M is sufficiently high, the rA becomes sufficiently low. Therefore,
the voltage drop due to the resistor rA is sufficiently smaller than the voltage drop
due to the resistors RD, RS. On the other hand, the current flows through the capacitance
CB with the change of VDX, VMX, but if M is sufficiently smaller than N - M, the value
cB is sufficiently smaller than cA and the voltage drop component of the current flowing
through cB due to the resistor rB becomes relatively very small. Namely, the voltage
VAX (or VBX) across both ends of the liquid crystal is substantially VDX - VMX when
the switch state SWA (or SWB) is at H and is substantially VSX - VMX when the switch
state SWA (or SWB) is at L, as shown in Fig. l0.
[0030] In the vicinity of the time Tp, the changes of VDX and VDM act in a direction which
reduces the effective values of both of VAX and VBX, but in the vicinity of the time
Tq, the change of VAX acts in a direction that reduces the effective value for VBX
and the changes of both VMX and VSX act in a direction that reduces the effective
value for VAX. Accordingly, it is believed that the difference between VAX and VBX
is affected more by the resistors RD, RS, RM than by the segment electrode output
resistance ro in Fig. 8.
[0031] Figure 11 shows the results of a simulation when the A and B groups described above
effect white and black opposite displays throughout all the rows, and Fig. 12 shows
the results of a simulation when the A group effects the white or black display but
the B group effects a gray display between white and black. In these drawings, the
symbols and names have the same meaning as in Fig. l0. The difference of these drawings
from Fig. l0 is that the current resulting from the change of SWB flows through CB
in Fig. 9, but this current component may be neglected because the value of CB is
sufficiently smaller than the value of CA, as already described. Accordingly, the
same concept as in Fig. 10 can be applied to Figs. Il and 12. Although an individual
explanation thereof is omitted, it is obvious from these results that the driving
effective voltage applied to the pixels of the A group drops at the time of a non-selection
and the driving effective voltage applied to the pixels of the B group rises more
than those of the:A group at the time of a non-selection. Since the liquid crystal
is assumed to be normally back, the display state becomes darker when the driving
effective voltage drops and becomes brighter when the driving effective voltage increases.
Therefore, the display state of a certain pixel in the A group becomes darker than
its original display state, and the display state of a certain pixel in the B group
becomes relatively brighter (brighter than the original display state in the cases
of Figs. l1 and l2, in particular). When the differences between the driving voltages
VAX and VBX applied to the pixels of the A and B groups during the non-selection period
are compared with one another for Figs. 10, 11 and 12, it can be understood that the
difference exists only near the time Tq in the case of Fig. 10, but the differences
exist both near the time Tp and the time Tq in the cases of Figs. 11 and 12. Naturally,
the difference occurs in those rows in which the display state of the B group is different
from the display state of the A group, and the difference of the driving effective
voltage throughout the non-selection period is determined by the number of such rows.
[0032] The explanation given above deals with the non-selection period, and the situation
becomes more complicated in the case of the selection period, as follows. If the dullness
of the waveform of the selection voltage (+Vc) is neglected, the A group gives a white
display in Fig. l0, for example, the common electrode drive voltage VYl should be
-Vc at the time Tp, and therefore, -Vc - VDX is applied to the pixels of the Y1 row
of the A group. Since the common electrode drive voltage VY2 should be +Vc at the
time Tq, +Vc - VSX is applied to the pixels of the Y2 row of the A group. Obviously,
the direction of the dullness of VDX, VSX in this case is the direction which reduces
the effective value in the selection period (the direction which darkens the white).
Conversely, when the A group effects the black display, the common electrode drive
electrode VY1 at the time Tp should be +Vc. Therefore, +Vc - VDX is applied to the
pixels of the Y1 row of the A group. Since the common electrode drive voltage VY2
should be -Vc at the time Tq, -Vc - VSX is applied to the pixels of the Y2 row of
the A group. In this case, it is obvious that the direction of the dullness of VDX
and VSX is the direction which increases the effective value in the selection period
(the direction which brightens black). It can be assumed from the above discussion
that the dullness of the drive voltage applied to the pixels of the A group during
the selection period acts in such a direction as to lower the contrast. For the pixels
of the B group, the same voltage as the voltage of the A group is applied to the pixels
of the B group having the same display as the A group, but for the display pixels
different from those of the A group, +Vc - VDX is applied at the time Tq when the
A group effects the white display, for example, and the effective value during the
selection period is not altered.
[0033] To summarize the above discussion, if N -M>> M in the example shown in Fig 9, the
following can be concluded.
(1) During the non-selection period, the driving effective voltage drops regardless
of the display state in the A group. The degree of the voltage drop depends on the
number of times of switching of the segment electrode voltage.
(2) During the non-selection period, the driving effective voltage increases more
in the B group than in the A group regardless of the display state. The degree of
this increase depends on the number of rows having a different display state from
the A group at the time of switching of the segment electrode drive voltage of the
A group.
(3) During the selection period, the driving effective voltage drops in the A group
when the display state changes from black to white. The driving effective voltage
increases when the display state changes from white to black.
(4) During the selection period, the driving effective voltage either increases, decreases
or does not change in the B group, depending on the display state.
[0034] The driving effective voltage practically applied to the liquid crystal must be calculated
throughout the selection period as well as throughout the non-selection period. Strictly
speaking, therefore, an extremely complicated calculation must be made, depending
on the display state. Therefore, it is assumed that the influences of the resistors
RD, RS and RM are great as the cause of the cross-talk or the drop of the contrast.
Accordingly, it must be concluded that the conventional concept is not sufficient,
and thus really effective counter-measures cannot be taken.
[0035] Figures 11 and 12 show the results of a simulation wherein all the columns (N columns)
of the liquid crystal display device are divided into two column groups (A group and
B group) and the number N - M of the columns of the A group is made sufficiently greater
than the number M of the columns of the B group, and Fig. 13. shows the results of
a simulation where the number of the columns of the A group is the same as that of
the B group. The timing relation in Fig. 13 corresponds to that of Fig. 11.Although
the difference of the effective value between VAX and VBX is clearly observed in Fig.
11, the difference of the effective value between VAX and VBX is not observed in Fig.
13. Namely, although cross-talk does not occur in this case, it is important to note
that the dullness of the waveform at each part in Fig. 13 is smaller than that in
Fig. ll. As already described, the effective value at the time of selection is affected
by the dullness of the waveforms of VDX and VSX. Since the dullness of VDX and VSX
is great in the case of Fig. 11, the deviation of the driving voltage applied to the
pixels during the selection period from the theoretical value is great, and the tendency
for the white portion to become dark and the black portion to become bright is strong,
so that the contrast drops even when the effective value during the non-selection
period is the same. In the case of Fig. 13, however, the dullness of VDX, VSX is small
and the drop of the contrast is also small. Paradoxically, the maximum contrast can
be obtained by displaying half of the screen in white and the other half in black;
if the screen is displayed as fully white or black and the difference between these
cases is considered, the lowest contrast can be obtained.
[0036] The cause of the difference of the dullness of the waveform between Figs. 1l and
l3 can be understood to be as follows. Figure 14(A) is an equivalent circuit diagram
when the case of Fig. l3 is used as an example is assumed that the capacitance of
the liquid crystal formed by the half of the screen is cx and RD, RS and RM are all
rx, for a simplification. At this time, the current Ix flowering from +Vs flows to
-Vs and the current does not flow towards the zero (0) potential. The time constant
Tx of the circuit at this time is (2·rx) (cx/2) = rx cx, and the dullness of the waveform
of the voltage applied across both ends of the liquid crystal of the A group is small,
as shown in Fig. 14(B).
[0037] Further, Fig. 15(A) is an equivalent circuit diagram corresponding to Fig. 11. Assuming
that the capacitance of the B group is much smaller than that of the A group, the
capacitance of the A group can be set to 2·(cx) by regarding the capacitance of the
B group as zero (0). At this time, the current flowing from +Vx flows fully towards
the zero (0) potential. The time constant Tx of the circuit at this time is (2·rx)·(2·cx)
= 4·rx·cx, and the dullness of the waveform of the voltage applied across both ends
of the liquid crystal of the A group becomes four times as great as that of Fig. l4,
as shown in Fig. l5(B). This difference of the time constants means that the difference
of four times also exists between the maximum and minimum dullness of the waveforms
of VDX and VSX.
[0038] Assuming that the effective value at the time of non-selection is equal, the difference
of the display state is determined by the difference of the effective values at the
time of selection, and since the effective value at the time of selection is affected
by the dullness of the waveforms of VDX, VSX, the difference of the dullness of the
waveforms VDX, VSX at the time of selection means the difference of the effective
value at the time of selection. Accordingly, the portion which should originally have
the same brightness becomes different depending on the display state. When the effective
values are calculated, the difference of four times of the time constants is a value
greater than four times.
[0039] A counter-measure for the cross-talk which takes the resistance of the power supply
lines into consideration has been very recently proposed ("SID 90 DIGEST, 4l2.21:
"Crosstalk-Free Drive Method for STN-LCDs" (hereinafter referred to as the "Reference
2")). Figure 3 of this reference depicts the resistor corresponding to RM of the present
invention, and the Reference 1 ascribes the voltage drop due to this resistor as one
of the causes of the cross-talk. To correct the influences of this voltage drop, the
Reference 1 adds a D.C. bias voltage ΔV to VM, which is defined in the present invention,
in each drive period of each row. The Reference 1 describes that the ΔV at this time
can be calculated from the difference between the number of pixels in the ON state
on the common electrodes which are now in the selection period, and the number of
pixels which are to be turned ON, on the common electrodes which are to be selected
next.
[0040] To state the conclusion first, this method is effective as a counter-measure for
the cross-talk, but this example does not fully consider the power supply resistors
RD, RS in the present invention. Since the Reference 2 is based on the concept that
the difference of the effective voltage during the non-selection period is offset
by the D.C. bias, the value ΔV described above is relatively small and the dullness
of the waveform does not change much. This means that, although the effective voltage
during the non-selection period can be made uniform, the influence of the dullness
of the waveform during the selection period is not greatly improved and the cause
of the cross-talk remains. In connection with the contrast and response also, improvements
are yet to be made as long as the influences of RD and RS exist. As described in the
Reference 2, this method is effective for a "frame gradation", but cannot be applied
so easily to those devices which effect a gradation display by changing the voltage
impression time during the selection period, as in a liquid crystal television receiver.
[0041] The value ΔV described above is calculated from the difference of the number of the
pixels in the ON state on the common electrodes that are currently in the selection
period, and the number of the pixels, which are to be turned ON, on the common electrodes
which are to be selected next. Nevertheless, even though the number of the pixels
turned ON during a certain selection period is the same, the timing at which the pixels
are turned ON is not always the same. In other words, there is the case where all
the pixels are simultaneously turned ON, and there is also another case whore the
pixels are turned ON individually or non-uniformly. Since the effective values turn
out different in both of these cases, a correction cannot be made. Since the capacitance
of the liquid crystal changes with the drive state, as already described, the capacitance
value, or the current value and thus the power supply voltage change, changes in a
complicated manner under a complicated drive state such as in the case of the gradation
display, and it is extremely difficult to maintain a predetermined correction state.
The change of the ambient temperature also must be taken into consideration when solving
this problem.
SUMMARY OF THE INVENTION
[0042] Therefore, an object of the present invention is to solve the problems resulting
from the dullness of the waveform, inclusive of the problem of the cross-talk described
above, in all display modes by bringing the drive voltage applied to both ends of
the liquid crystal as close as possible to an ideal state.
[0043] The influences of the resistance of each part (the output resistance of the power
supply, the wiring resistance inside the drive integrated circuit, the wiring resistance
inside the panel, etc.) that result in the dullness of the waveform are the influences
of the voltage drop brought forth by the current that flows through the resistance
of each part. This current flows into and out of the common electrode drive circuit
and the segment electrode drive circuit through the liquid crystal, which is a capacitive
load, and leads to the voltage drop when it flows through the resistance of each part,
so that a voltage different from the external voltage given is eventually applied
to the liquid crystal. The present invention is based on the premise that the voltage
drop always exists, regardless of the degree thereof, pays specific attention to the
resistance that exists parasitically in the power supply system and exerts a particularly
great influence, detects the current that brings such a voltage drop to the resistance,
and changes the external voltage to be given to the drive circuit in accordance with
this current quantity, to thus solve the problem described above.
[0044] Figure 16 is an explanatory view explaining the fundamental concept of the present
invention. When the circuit shown in Fig. 16(A) is considered and the voltage waveform
to be applied to the point V and the voltage waveform at the point E corresponding
to the former are considered, the dullness of the waveform at the point E is great
as shown in fig. 16(B) if a step-like voltage waveform is applied to V, but is small
if an impulse-like correction voltage is added to the voltage to be applied to the
point V as shown in Fig. 16(C). The means for solving the problems, employed in the
present invention on the basis of such a concept, comprises the following. Namely,
in a display device including a display panel having common electrode groups and segment
electrode groups, a common electrode driving circuit and a segment electrode driving
circuit, the present invention detects a current quantity flowing through the display
panel, and is constituted such that:
(1) the common electrode drive voltage applied to the common electrode group through
the common electrode drive circuit is adjusted in accordance with the current value;
and
(2) the segment electrode drive voltage applied to the segment electrode group through
the segment electrode drive circuit is adjusted in accordance with the current value.
[0045] In accordance with the present invention, the voltage drop induced by the current
flowing through the display panel is adjusted by detecting this current, so that the
driving voltage applied to the liquid crystal approaches the ideal state in all conditions,
whereby the contrast and response are improved and cross-talk is greatly reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046]
Fig. 1 is a structural circuit view showing a first embodiment of the present invention;
Fig. 2 is a structural view showing the structure of a simple matrix type liquid crystal
display device;
Fig. 3 is a structural view showing an example of a liquid crystal driving circuit;
Fig. 4 is an operation waveform diagram showing an example of an ideal liquid crystal
driving voltage waveform;
Fig. 5 is an explanatory view of the influences of cross-talk;
Fig. 6 is a conventional explanatory view explaining the cross-talk;
Fig. 7 shows a model of a liquid crystal drive system is based on the conventional
explanation;
Fig. 8 shows a first model of a liquid crystal drive system according to the present
invention;
Fig. 9 shows a second model of the liquid crystal drive system fabricated according
to the present invention;
Figs. 10 to 13 are explanatory views of the present unsolved problems, on the basis
of the results of a simulation of the second model;
Figs. 14 and 15 are explanatory views of the difference of the degree of dullness
of the waveform in accordance with the display state;
Fig 16 is an explanatory view of the basic concept of the present invention;
Fig. 17 and 18 are explanatory views of embodiments of a current detection means and
a voltage control means;
Fig. 19 is a structural view showing the first embodiment of the present invention
applied to the liquid crystal drive system model shown in Fig. 9;
Figs. 20 to 22 are explanatory views of the effects of the present invention, on the
basis of results obtained by simulating the structure shown in Fig. 19;
Figs. 23 to 28 are views illustrating a first to a sixth aspects of the present invention,
respectively;
Fig. 29 is a structural circuit diagram showing the second embodiment of the present
invention;
Fig. 30 is an explanatory view of the second embodiment of the present invention applied
to the liquid crystal drive system model shown in Fig. 9;
Fig. 31;(A) and Fig. 31(B) are structural circuit diagram showing a third embodiment
of the present invention;
Fig. 32 is a structural circuit diagram showing the fourth embodiment of the present
invention;
Fig. 33 is an explanatory view of the third embodiment of the present invention applied
to the liquid crystal drive system model shown in Fig. 9;
Fig. 34 is a structural circuit diagram showing the fifth embodiment of the present
invention;
Fig. 35 is a structural circuit diagram showing the sixth embodiment of the present
invention;
Fig. 36 is a structural circuit diagram showing the seventh embodiment of the present
invention;
Fig. 37 is a structural circuit diagram showing the eighth embodiment of the present
invention;
Fig. 38 is a waveform diagram showing an example of a liquid crystal drive waveform
different from that used for the explanation of the present invention; and
Fig. 39 is an explanatory view of the present invention when applied to the example
shown in Fig. 38.
Fig. 40 is a view illustrating a positive feed-back circuit formed in an adjusting
circuit as shown in Fig. 1;
Fig. 41 is a view illustrating a positive feed-back circuit formed in an adjusting
circuit as shown in Fig. 29; and
Fig. 42 is a view illustrating a positive feed-back circuit formed in an adjusting
circuit as shown in Fig. 34.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] An electrooptical display device of the present invention basically has a technical
construction such that the electrooptical display device comprises a display panel
having common electrode group and segment electrode group, a display device having
a common electrode driving circuit and a segment electrode driving circuit and an
adjusting circuit provided with a current detection means for detecting current flown
through said display panel and a voltage control means for controlling a driving voltage
applied to both terminals of the display device and which is provided between a driving
power source of said display device and said display device wherein said adjusting
circuit operates so that said voltage control means is operated in response to an
output signal output from said current detection means to correctly adjust a deformation
of a wave-form of a driving voltage applied to both terminals of said display panel.
[0048] In accordance with a first aspect of the present invention, the electrooptical display
device is constructed as shown in Figs. 23 and 24, in which a current detection means
of an adjusting circuit is connected any one of said common electrode driving circuit
and a segment electrode driving circuit, while a voltage control means thereof is
connected to an opposite electrode driving circuit to which the common electrode driving
circuit connects.
[0049] In accordance with a second aspect of the present invention, the electrooptical display
device is constructed as shown in Figs. 27 and 28 in which a current detection means
of the adjusting circuit is connected any one of the common electrode driving circuit
and the segment electrode driving circuit, while the voltage control means thereof
is connected to the same electrode driving circuit to which the common electrode driving
circuit connects.
[0050] In accordance with a third aspect of the present invention, the electrooptical display
device is constructed in which a current detection means and the voltage control means
of the adjusting circuit are connected both of the common electrode driving circuit
and the segment electrode driving circuit.
[0051] In accordance with a fourth aspect of the present invention, the electrooptical display
device is constructed as shown in Fig. 27 or 28, in which a current detection means
of the adjusting circuit is connected any one of the common electrode driving circuit
and the segment electrode driving circuit, while the voltage control means thereof
is connected to both of the common electrode driving circuit and the segment electrode
driving circuit.
[0052] In accordance with a fifth aspect of the present invention, the electrooptical display
device is constructed as shown in fig. 26, in which a current detection means is connected
to the common electrode driving circuit and a plurality of segment electrode driving
voltage control means are connected to said segment electrode driving circuit and
to a plurality of said segment electrode driving voltage sources, wherein each one
of said segment electrode driving voltage control means is controlled by an output
signal output from said current detection means.
[0053] In accordance with a sixth aspect of the present invention, the electrooptical display
device is constructed as shown in Fig. 25, in which a voltage control means is connected
to the common electrode driving circuit and a plurality of sequment electrode driving
current detection means are connected to the segment electrode driving circuit and
to a plurality of the segment electrode driving voltage sources, wherein the common
electrode voltage control means is controlled by each one of output signal output
from the each one of the current detection means.
[0054] In accordance with a seventh aspect of the present invention, the electrooptical
display device is constructed as shown in Figs. 27 and 28, in which both of the current
detection means and a fist voltage control means of the adjusting circuit are connected
to any one of the common electrode driving circuit and segment electrode driving circuit
and the adjusting circuit is further provided with a second voltage control means
separate from the first voltage control means which is connected to an opposite electrode
driving circuit to which the first voltage control means connects.
[0055] The preferred embodiments of the present invention will be explained with reference
to Figures with respect to each one of the aspects of the present invention as mentioned
above.
[0056] Figure 1 shows the first embodiment of the present invention, and corresponds to
a first aspect of the present invention as shown in Fig. 23 or 25. In Fig. 1, a correction
circuit 100 is constituted as follows. A potential EA is applied to the positive input
terminal of a first differential amplifier 101 and the output terminal of this first
differential amplifier 101 is fed back to the negative input terminal of the first
differential amplifier 101 through a resistor Ra, and is connected to the negative
input terminal of a third differential amplifier 103 through a resistor r. A potential
EB is applied to the positive input terminal of a second differential amplifier 102
and the output terminal of this second differential amplifier 102 is fed back to the
negative input terminal of the second differential amplifier 102 and is connected
to the negative input terminal of the third differantial amplifier 103 described above.
The potential EA is applied to the positive input terminal of the third differential
amplifier 103 through a resistor Rx and the potential EB is applied thereto through
the resistor Rx. The output terminal of this third differential amplifier 103 is fed
back to the negative input terminal of the third differential amplifier 103 through
the resistor R. The output VH is taken out from the negative input terminal of the
first differential amplifier 101, the output VL, from the negative input terminal
of the second differential amplifier 102 and the output VM, from the output terminal
of the third differential amplifier 103.
[0057] Note that, in the first embodiment, two current detection means 3-1, and 3-2, and
a voltage control means 4 are provided in the adjusting circuit 100.
[0058] This circuit will be explained with reference to Figs. 17 and 18. The circuit shown
in Fig. 17 is a well known current detection circuit. Assuming that the current flowing
from the output V to a load is I, the following relationship can be established:

The output VM in the circuit shown in Fig. 18 is given as follows:

Therefore, assuming that the current flowing out of the output VH is IH and the current
flowing into the output VL is IL in the circuit shown in Fig. 1, the following relationship
can be established:


Accordingly, VM takes the value obtained by subtracting the voltage proportional
to IH from the intermediate voltage between EA and EB, and adding the voltage proportional
to IL to the balance.
[0059] When the adjusting circuit 100 shown in Fig. 1 is applied to Fig. 9, the circuit
structure becomes as shown in Fig. 19, i.e., if EA = +Vs and EB = -Vs, then,


Therefore, when IH flows and VMX rises, VM drops in proportion to IH and lowers VMX.
If IL flows and VMX drops, VM rises in proportion to IL and raises VMX. The proportional
constants to be applied to IH and IL are regulated by maling R variable.
[0060] Figures 20, 21 and 22 show the results of a simulation during the non-selection period,
using the structure shown in fig. 19, when the proportional constant is set to a certain
value. The timing relationships in these diagrams correspond to those of Figs. 10,
11 and 12, respectively. The explanation will be given for Fig. 20.
[0061] When the switch state SWA described above changes from L to H at the time Tp, a current
IH flows from VH to VM. This current is used to raise the potential of VMX, but since
the adjusting circuit 100 described above lowers the potential of VM by the voltage
component proportional to IH, as a result VMX does not rise but drops. At the time
Tq, the switch state SWA changes from H to L and a current IL flows from VM to VL
and is used to lower the potential of VMX, but since the adjusting circuit 100 raises
the potential of VM by the voltage component proportional to IL, as a result VMX is
not lowered but rises.
[0062] In consequence, the change of VDX acts in a direction that will lower the effective
values for both VAX and VBX near the time Tp, but conversely, the change of VMX acts
in a direction that will raise the effective values. This change acts in a direction
that will lower the effective value of VMX in connection with VBX. As a result of
these synthetic operations, the effective values of VAX and VBX approach in a direction
such that they become equal to each other.
[0063] It is important to note that the operation described above operates as a positive
feedback. Namely, the current IH flows on the basis of the potential difference between
VH and VM, but when the current IH flows, VM is lowered in proportion to this value,
and thus the positive feedback operation makes the value IH greater and greater, and
decreases the value VM with the former. As a result, IH instantaneously becomes a
large current and provides the following effect.
[0064] Generally, when the charge/discharge characteristics of the capacity are considered,
the voltage across both ends of the capacity is proportional to the integration value
of the charge/discharge current. In the case of a charge/discharge at a small current,
the voltage across both ends of the capacity changes slowly and the dullness is great.
On the contrary, in the case of charge/discharge at a large current, the voltage across
both ends of the capacity changes sharply and the dullness is small. Namely, in accordance
with this embodiment, the liquid crystal as the capacitive load is instantaneously
charged/discharged due to the afore-mentioned positive feedback operation, and the
dullness of the driving voltage waveform applied to both ends of the liquid crystal
is remarkably improved and approaches the ideal drive state. The time td shown in
Fig. 20 is depicted on a greater scale than the practical simulation result to enable
the effects of the present invention to be more esaily understood.
[0065] The explanation for Figs. 21 and 22 will be omitted because the same concept as described
above also can be applied. It should noted that the effective values of VAX and VBX
are regarded as being equal throughout all of Figs. 20 , 21 and 22. This can be understood
more clearly when compared with Figs. 10, 11 and 12. Namely, the effective values
of VBX shown in Fig. 11 and VBX shown in Fig. 12 can be regarded as equal, but the
effective value of VBX shown in Fig. 10 cannot be regarded as equal to these two.
In contrast, in Figs. 20, 21 and 22, the difference of the effective voltage values
carrot be observed between VAX or between VBX, and the difference of the effective
value also cannot be observed between VAX and VBX.
[0066] The explanation given above relates to the non-selection period. For the selection
period, the differences of VDX, VSX do not exist from Fig. 20 to Fig. 22 and the time
td is sufficiently small, as already described. According to the theory of the liquid
crystal, the voltage change having a sufficiently short time need not be included
in the calculation of the effective value from the response property of the liquid
crystal, as already described, and from the practical point of view, it can be considered
that there is no substantial difference in the drive force of the liquid crystal in
the selection period between Figs. 20 to 22 and Fig. 13. In contrast, in the cases
of Figs. 10 to 12, the dullness of the waveform is gentle and the drive force of the
liquid crystal is affected accordingly.
[0067] Figure 29 shows the second embodiment of the present invention corresponding to the
fourth aspect of the present invention as shon in Fig. 24 or 26. In Fig. 29, the adjusting
circuit 230 is provided with a current detection means 3 and two voltage control means
4-1 and 4-2 and it is specifically constituted as follows. The input EA is connected
to the point P2 through the resistor r and this point P2 is connected to the positive
input terminal of the second differential amplifier 232. The input EB is connected
to the point P3 through the resistor r and this point P3 is connected to the positive
input terminal of the third differential amplifier 233. The point P2 described above
is further connected to the point P1 througth the resistor r and this point P1 is
connected to the positive input terminal of the first differential amplifier 231 and
is connected also to the point P3 through the resistor r. The output terminal P4 of
this first differential amplifier 231 is fed back to the negative input terminal of
the first differential amplifier 231 through the resistor Ra, to the negative input
terminal of the second differential amplifier 232 through the resistor R, and further,
to the negative input terminal of the third differential amplifier 233 through the
resistor R. The output terminal of the second differential amplifier 232 is fed back
to the negative input terminal of the second differential amplifier 232 through the
resistor R. The output terminal of the third differential amplifier 233 is fed back
to the negative input terminal of the third differential amplifier 233 through the
resistor R. The output VH is taken out of the output terminal of the second differential
amplifier 232, the output VL, from the output terminal of the third differential amplifier
233 and the output VM, from the negative input terminal of the first differential
amplifier 231.
[0068] Assuming that the potentials at the points P1, P2, P3 and P4 are VP1, VP2, VP3 and
VP4 and the current flowing out of the output VM to the load is IM, in the circuit
construction shown in Fig. 29, then the following relationships stand:


At this time, the outputs VH, VL and VM are given as follows, as:is obvious from
the functions of the differential amplifiers:


Namely, an intermediate potential between EA and EB is output to VM, and the potentials
obtained by subtracting the change components proportional to the current IM from
EA, EB are output to VH and VL, respectively. VM, however, is corrected in accordance
with the current flowing out of VH, VL in the first embodiment, but VH and VL are
adjusted in accordance with the current flowing out of VM in this second embodiment.
[0069] Assuming that, in the correction circuit 230 shown in Fig. 29, EA = +Vs and EB =
-Vs, then,

The results obtained by simulating this circuit by the adjusting circuit 100 shown
in Fig. 19 are illustrated in Fig. 30. The timing relationship of Fig. 30 is the same
as those of Figs. 10 and 20. When the switch state SWA changes from L to H at the
time Tp in Fig. 30, a current -Im flows from VH to VM in Fig. 29 and VMX rises in
the positive direction due to this current. As a result, VH and VL rise by Ra·Im.
At this time, VH, IM and VM have the relationship of a positive feedback, and IM,
which attains a large current, completes a charge and discharge of the liquid crystal
of the aforementioned group A within a short time. When the switch state SWA changes
from H to L at the time Tq, a current IM flows from VM to VL in Fig. 29, and VMX drops
in the negative direction due to this current. As a result, VH and VL drop by Ra·IM.
At this time, VL, IM and VM have the relationship of a positive feedback and IM completes
a charge and discharge of the liquid crystal of the group A within a short time. All
the operations are finished within an extremely short time, so that the voltages applied
to both ends of the liquid crystals of the groups A and B become VAX and VBX, as shown
in Fig. 30, and the dullness of the waveforms can be greatly improved. No difference
of the effective value is observed between VAX and VBX, and the waveforms are obviously
approximate to the original ideal waveforms.
[0070] In the first and second embodiments described above, the effects of the present invention
are not substantially observed when the capacitance values formed by the groups A
and B are equal to each other, and they are driven under completely opposite states.
Namely, the condition in this case is such that the value of the current flowing in
each group is equal and the current does not flow through the resistor RM, as explained
with reference to Fig. 14. Therefore, in the first embodiment, the absolute values
of the currents IH and IL in Fig. 1 are equal to each other, and since their polarities
are opposite, the correction quantities are offset and become zero (0), so that VM
is not adjusted. In the second embodiment, on the other hand, the value of the current
IM in Fig. 29 becomes 0, so that VH and VL are not corrected. As described above,
however, the quantity of the dullness of the waveform when the capacitance values
formed by the groups A and B are equal is originally one-fourth of the maximum value.
Furthermore, since the influences on the liquid crystal drive force become much smaller
when the dullness of the waveform becomes small, as described already, the first and
second embodiments can provide sufficient effects in almost all cases. Namely, a contrast
substantially approximate to the theoretical limit can be obtained and the response
also can be improved.
[0071] The first embodiment as explained above, shows an adjusting circuit in which current
flown through said segment electrode is detected by the current detection means and
the common electrode driving voltage is controlled by the output signal output from
the current detection means and the second embodiments as explained above, shows an
adjusting circuit in which current flown through said common electrode is detected
by the current detection means and the segment electrode driving voltage is controlled
by the output signal output from the current detection means.
[0072] In the present invention, the segment electrode driving voltage may be controlled
by detected signal of the current detection means detecting current flown through
the segment electrode or the common electrode driving voltage may be controlled by
detected signal of the current detection means detecting current flown through the
segment electrode.
[0073] Fig. 31(A) shows the third embodiment corresponding to the second aspect of the present
invention as shown in Fig.s 27 and 28.
[0074] In Fig. 31(A), an adjusting circuit 100 having a function by which current flown
through the common electrode is detected first by a current detection means and then
the common electrode driving voltage is controlled by the detected signal output from
the current detection means, is disclosed.
[0075] Note that in Fig. 31(A), both of reference voltages EA and EB are applied to a positive
input terminal of an operational amplifier 400 through a resister r, respectively,
and further an output of the operational amplifier 400 is positively fed back to the
positive input terminal thereof through serially arranged resister Rf and capacitance
Cf while an output of the operational amplifier 400 is negatively fed back to a negative
input terminal thereof through a resister R and an output signal VM is output from
the negative input terminal of the operational amplifier 400.
[0076] The operational mode of this embodiment is explained as follows.
[0077] When current IM is flown in this circuit, the output of the operational amplifier
400 is increased by IM. Ra and this amount of change is positively fed back to positive
input terminal of the operational amplifier 400 through the capacitance Cf and thereby
a voltage the output terminal thereof is steeply increased to cause an output voltage
VM increased.
[0078] Therefore, current IM is also increased and thus rapid charge-discharge operation
is carried out in the capacitance of the liquid crystal whereby a deformation of wave-form
of voltage applied to both end terminals o the liquid crystal can be corrected.
[0079] In accordance with this adjusting method, it is apparent that the current flown through
the segment electrode is detected first by a current detection means and then the
segment electrode driving voltage is controlled by the detected signal output from
the current detection means.
[0080] And further, this embodiment can be combined with the first or the second embodiment.
[0081] Note, that when a parasitic resistance value is large or a capacitance formed is
large due to a surface area thereof being large, value rx·cx as shown in Fig. 14 is
increased to an extent at which a deformation of the wave-form of the electrode driving
voltage adversely effects to a driving force of the liquid crystal and thus a sufficient
improved effect could not be obtained in the first or the second improved effect could
not be obtained in the first or the second embodiment.
[0082] In such a case, it is prefer the third embodiment as shown in Fig. 31(A) is combined
with the first or second embodiment.
[0083] On the other hand, a deformation of a wave-form of a high driving voltage applied
to the electrode during one selected period can be adjusted by detecting current flown
through power source lines +Vc and -Vc as shown in Fig. 3, and self-controlting the
voltage of the power source lines.
[0084] This embodiments is shown in Fig. 31(B) and in which a first adjusting circuits 401
is provided between the power source lines +Vc and common electrode driving circuit
403 and a second adjusting circuit 402 is provided between the power source lines
+Vc and common electrode driving circuit 403, respectively.
[0085] Each of the adjusting circuits 401 and 402 has the same circuit construction as shown
in Fig. 31(A) and thus an explanation about the operation thereof is omitted.
[0086] Note, that this embodiment may be combined with another embodiment. Fig. 32 shows
a fourth embodiment of the present invention and in this embodiment, the first embodiment
as shown in Fig. 1 and the third embodiment in which the segment electrode driving
voltage is controlled by detecting current flown in the segment electrode utilizing
the circuit construction as shown in Fig. 31(A) are combined.
[0087] In accordance with this embodiment, a driving condition of the liquid crystal can
be changed into more ideal an optimal condition.
[0088] As apparent from Fig. 32, an adjusting method is disclosed in which current flown
through the liquid crystal is detected first, and then both driving voltages applied
to the common electrode and the segment electrode, respectively, are simultaneously
controlled.
[0089] This embodiment as shown in Fig. 32, may be considered that a new function is added
to the adjusting circuit of the first embodiment as shown in Fig. 1 and therefore,
the same component of Fig. 32 as used in Fig. 1 is labelled with the same reference
as used in Fig. 1 and thus an explanation a bout an operation thereof is omitted.
[0090] Note, that the adjusting circuit 250 shown in Fig. 32 is additionally provided with
the following new function compared with the circuit of the first embodiment as shown
in Fig. 1;
[0091] A reference voltage EA is applied to a positive input terminal of a first operational
amplifier 101 through a resister Ri and the positive input terminal is connected to
an output thereof trough a circuit in which a resister Rf and a capacitor Cf are serially
arranged.
[0092] On the other hand, a reference voltage EB is applied to a positive input terminal
of a first operational amplifier 102 through a resister Ri and the positive input
terminal is connected to an output thereof through a circuit in which a resister Rf
and a capacitor Cf are serially arranged.
[0093] In Fig. 32, the function of the portion added to Fig. 1 is as follows. When the current
IH flows, the voltage proportional to this current develops as the change component
at the output terminal of the first differential amplifier 101. Since this voltage
change component is fed back positively to the positive input terminal of the first
differential amplifier 101 through the series circuit of the resistor Rf and the capacitor
Cf, the potential at the output terminal of the first differential amplifier 101 rises,
so that the potential of the output VH rises but the output VM drops. Then, the current
IH increases and the output potential of the first differential amplifier further
rises due to the positive feedback operation described above. When the current IL
flows, the output VL drops rapidly while the output VM rises rapidly. These operations
are finished in an extremely short time due to the positive feedback operation. The
Rf in this circuit regulates the positive feedback quantity and suppresses the oscillation
of the circuit.
[0094] Since a new feedback is added, the value of the constant at each portion of the correction
circuit 250 becomes different from that of Fig. 1. Figure 33 shows the results of
a simulation carried out by optimizing these constants and combining the liquid crystal
drive system model shown in Fig. 9. The timing relationships shown in Fig. 33 correspond
to those shown in Figs. 11 and 21. As can be seen, substantially complete and ideal
drive waveforms can be obtained except for spikes of an extremely short period (not
shown), even when the difference of the capacitance values of the groups A and B are
0 and when the difference of the capacitance values is maximum.
[0095] Figure 34 shows a more definite embodiment, i.e., a fifth embodiment, obtained by
simplifying the embodiment shown in Fig. 1, as although the embodiment shown in Fig.
1 provides remarkable effects, it is not free from the following problems:
(1) The dullness of the waveform is a phenomenon having a high speed of up to 1 µS,
and it is necessary to output a relatively large current having a large amplitude,
instantaneously, in addition to the high speed of from some dozens to about 100 nS.
(2) Generally, high speed amplifiers satisfying the requirement (1) consumed a large
amount of current and cannot be easily applied to compact apparatuses.
(3) Generally, high speed amplifiers satisfying the requirement (1) are very expensive,
and the practice of the invention is therefore limited.
[0096] The embodiment shown in Fig. 34 is directed to solving the problems described above,
and can provide the required effects at a reduced cost. In Fig. 34, the correction
circuit 270 is constituted as follows. The negative input terminal of the differential
amplifier 271 is connected to the potential Ea through the resistor r, to the potential
EB through the resistor r, and further, to the output terminal VM of the differential
amplifier 271 through the resistor R. The other output terminal VH is connected to
the potential EA through the:resistor Ra and to the positive input terminal of the
amplifier 271 described above through the resistor Rx. Furthermore, the other output
terminal VL is connected to the potential EB through the resistor Ra and to the positive
input terminal of the differential amplifier 271 through the resistor Rx.
[0097] In this circuit construction, the outputs are given as follows:


When the simulation is carried out by replacing the correction circuit 270 shown
in Fig. 34 by the correction circuit 100 shown in Fig. 19, it is found that substantially
the same result can be obtained as in Figs. 20 to 22, by appropriately selecting the
constants by sufficiently reducing the Ra value, or the like. Since the number of
differential amplifiers may be smaller in the embodiment shown in Fig. 34 than in
the embodiment shown in Fig. 1, the problems with the embodiment of Fig. 1 can be
easily solved.
[0098] In the circuit construction shown in Fig. 2, either one, or both, of the segment
electrode drive circuit 201 and the common electrode drive circuit 202 are sometimes
disposed inside the display panel. In the active type liquid crystal panel, for example,
transistors are fabricated inside the panel and these drive circuits are assembled.
In the passive liquid crystal panel, on the other hand, the drive integrated circuit
is disposed on the panel in accordance with the system referred to as "COG (Chip On
Glass)". In these cases, the drive voltages applied to the liquid crystal are supplied
to the drive circuits from outside the panel, through the wirings inside the panel,
and since the wirings inside the panel generally have a high specific resistance,
this resistance which can not be neglected.
[0099] In Japanese Patent Unexamined Publication (Kokai) No. 2-90280 (hereinafter referred
to as the "reference 2"), the Applicant of the present invention proposed:
(1) An electrooptical display device characterized by including outgoing electrodes
for detecting the potential at a specific point inside a display panel; and
(2) A method of driving an electrooptical display device characterised by detecting
the potential at a specific point inside a display panel and effecting a control such
that the potential at said specific point reaches a specific value.
In this technology is applied to the present invention, more effective effects can
be obtained.
[0100] Figure 35 is a structural view of the sixth embodiment, showing the technology proposed
in the reference 2 applied to the embodiment of the present invention shown in fig.
34. This circuit assumes a passive liquid crystal panel wherein the segment electrode
drive circuit 301 and the common electrode drive circuit 306 shown in Fig. 3 are disposed
inside the display panel 280 by COG. In Fig. 35, the segment electrode drive power
supply line of the segment electrode drive circuit 301, to which VH(+Vs) is supplied,
is taken out to the outside through the wiring resistance (inclusive of the connection
resistance for external connection; hereinafter the same) Rp inside the panel, is
applied with EA and is taken out through the wiring resistance Ro. Furthermore, it
is connected to the positive input terminal of the differential amplifier 271. The
segment electrode drive power supply line, to which VL(-Vs) is supplied, is taken
out through the wiring resistance Rp inside the panel, is applied with EB and is taken
out to the outside through the wiring resistance Ro. Furthermore, it is connected
to the positive input terminal of the differential amplifier 271. The common electrode
drive power supply line of the common electrode driving circuit 306, to which VM(0)
is supplied, is taken out through the wiring resistance Rq inside the panel, is connected
to the output terminal of the differential amplifier 271, is taken out through the
wiring resistance Rs and is further connected to the negative input terminal of the
differential amplifier 271. The potential EA is applied to the negative input terminal
of the differential amplifier 271 through the resistor r, and EB is supplied further
through the resistor r.
[0101] In the embodiment shown in Fig. 35, the wiring resistance Rp itself inside the panel
280 plays the role of the current detection resistor Ra shown in Fig. 34. If such
a construction is employed, it is not necessary to dispose the currant detection resistor
outside. Accordingly, the resistance values of the EA and EB power supply lines need
not be increased, and thus the possibility of increasing the dullness of the waveform
of the segment electrode driving voltage applied to the liquid crystal through the
segment electrode driving circuit 301 is eliminated. The resistor Rx in Fig. 34 is
replaced in Fig. 35 by Rx + Ro but it is only necessary that this resistor be sufficiently
greater than Ra (Rp), and the addition of Ro does not exert an adverse influence on
the circuit operation. Furthermore, the resistor R in Fig. 34 is R + Rs in Fig. 35,
but since R is the variable resistor, the value R + Rs may be considered as falling
withing the range of adjustment. Since the adjustment ratio R/r can be made small
because the detecting position of the potential to be fed back to the negative input
terminal of the differential amplifier 271 changes, the resistor r can be set a relatively
large value and a bleeder current flowing from EA to EB through the resistor r can
be reduced.
[0102] It is obvious that the technology proposed in the reference 1 can be applied to the
embodiments shown in Figs. 1, 29 and 32 of the present invention. Figure 36 shows
the application of the technology of the reference 1 to the embodiment shown in Fig.
1 of the present invention refered to the seventh embodiment, and this can further
improve the characteristics. Like reference numerals are used in this drawing to identify
like constituents as in Fig. 1 and the explanation of such members is omitted. In
Fig. 36, the resistor Ra in Fig. 1 is replaced by the wiring resistance Rp inside
the panel 290. The wiring resistance Rs inside the panel 290 is added to the resistor
R in Fig. 1. Here, the differential amplifier 101 in Fig. 36 operates in such a manner
that the potential of VH in Fig. 36 is kept at a constant potential EA, and the differential
amplifier 102 operates in such a manner that the potential of VL in Fig. 36 is kept
at a constant potential EB, so that the current drop component of the resistor Rp
is corrected and the same effect can be thus obtained so that RD and RS of the model
shown in Fig. 9 become extremely small. Accordingly, the dullness of the waveforms
of VDX, VSX is greatly reduced, and more remarkable effects can be obtained.
[0103] Figure 37 shows the eighth embodiment of the present invention, wherein an inductor
is utilized for the current detection. The output VH(+Vs) is connected to EA through
the inductor L1 and the output VL(-Vs) is connected to EB through the inductor L1.
The output VM is connected to the output terminal of the differential amplifier 320
and to the negative input terminal of the differential amplifier 320 through the series
circuit of the resistor R and the capacitor CL. This input terminal is grounded through
the resistor r and through another inductor L2, which is coupled with the inductor
L1 coupled to +Vs, with a coupling coefficient M, and is further grounded through
the resistor r and through the inductor L2, which is connected to the inductor L1
connected to -Vs, with the coupling coefficient M. The positive input terminal of
the differential amplifier 320 is grounded.
[0104] Figure 37 will be explained briefly. When the current IH flows, for example, a voltage
obtained by differentiating the current IH develops at the inductor L2 coupled with
the inductor L1 which is connected to EA. This voltage is integrated by the integration
circuit consisting of the differential amplifier 320 and the capacitor CL, and a voltage
proportional to the current IH develops at the output terminal VM of the differential
amplifier 320. When the current IL flows, on the other hand, a voltage obtained by
differentiating the current IL develops at the inductor L2 coupled with the inductor
L1 which is connected to EB. This voltage is integrated by the integration circuit
consisting of the differential amplifier 320 and the capacitor CL, and a voltage proportional
to the current IL develops at the output terminal VM of the differential amplifier
320. The values of L1 and L2 are extremely small and can be formed easily by the wirings
alone, by designing the wirings on the printed board. Note, a circuit for defining
the portion corresponding to the integration constant must be added to Fig. 37, although
such a circuit is not shown in Fig. 37.
[0105] As is obvious from the description given above, the present invention brings the
effective voltage values in the non-selection and selection periods to the theoretical
values by correcting the waveform of the liquid crystal driving voltage to the original
ideal waveform in all the conditions inclusive of a gradation display, can solve not
only the problems resulting from the dullness of the waveform such as the drop of
constrast and deterioration of response, but also the cross-talk. Since the present
invention detects the current that actually flows through the liquid crystal, the
invention can obviously make a stable correction against the complicated changes of
the current in a gradation display and against environmental changes. The display
device obtained by actually practicing the present invention provides an excellent
display quality. Note, since the power supply is changed when practicing the present
invention, the relationship between potentials of the latch-up circuit and the like
must be examined and counter-measures therefor should be taken. However, such measures
will be omitted as they are irrelevant to the gist of the present invention. When
the panel is divided into upper and lower two parts and the displays of these two
parts are different as explained with reference to Figs. 5(C) and 5(D), the present
invention must be applied individually to these two parts. If the same display is
effected for the two parts, however, the present invention can be applied in common
to both.
[0106] The effects obtained by the present invention can be summarized as follows. Since
the present invention drives the liquid crystal under the ideal state, it can provide
a display device having an excellent performance in that:
(1) the theoretically greatest contrast can be obtained;
(2) the device is free from cross-talk;
(3) the response can be improved; and
(4) the display device can be applied even to devices having a gradation display,
such as a liquid crystal television receiver.
Thus, the effects of the present invention are very high. Recently, the load on the
drive circuit is increased because a greater number of pixels are incorporated in
the display device, the display device must effect a color display, and the screen
is enlarged. In addition, a packaging system called the "COG (Chip On Glass) system",
for example, has been adopted, and the condition associated with the parasitic resistance
tends to get worse. Nonetheless, the present invention can fully exhibit sufficient
effects and can contribute greatly to the development of the display devices. Note,
the parasitic resistance of each part as the real cause of the problems must be further
continued because the present invention is intended to solve the problems from the
aspect of the drive circuit, although the present invention provides very high effects.
[0107] Finally, some additional remarks on the present invention will be made.
(1) The foregoing description is given on the liquid crystal display device. As is
obvious from the description, however, the present invention is effective for an EL
display device, for example. Therefore, the range of the application of the present
invention is not particularly limited to the liquid crytal display device.
(2) The definite drive mothods of the display device are diversified as already described.
Besides the drive method used for the explanation, there is a method which drives
the segment electrodes and the common electrodes by the use of the drive voltages
shown in Fig. 38, for example However, the drive method of Fig. 38 becomes the one
shown in Fig. 39 when the potential of the common electrode driving voltage Vcom is
considered as the reference (0), and the present invention can be obviously applied
thereto, as well. Accordingly, the present invention is not particularly limited to
the drive method explained herein. Note, that, when the present invention is applied
to fig. 38, the adjusting operation as shown in the present invention, may be carried
out in a selected period.
(3) The definite embodiments of the present invention are not particularly limited
to those described herein.
(4) For example, the first embodiment shown in Fig. 1 represents the method which
detects both the currents flowing through the input voltages EA and EB and controls
the output voltage VM. It has been confirmed, however, that the effects of the invention
can be obtained if the control quantity is changed even when either one of EA and
EB is used for controlling VM. Accordingly, the present invention is not particularly
limited to the detection of all the currents that flow through the liquid crystal.
(5) The detailed description of the invention given above has concentrated on the
simple matrix type liquid crystal display device, but in "active type matrix display
devices" also a write operation is effected at the time of the selection of rows,
and consequently, the power supply lines change. As a result, the correct quantity
of charge is not charged or discharged; and thus the contrast drops and response drops
in some cases. The present invention also can be applied to such cases and can obviously
provide great effects. Accordingly, the present invention is not particularly limited
to the simple matrix type display device.
(6) Similarly, in the case of the display structure which does not constitute the
matrix (such as the structure referred to as the "segment type"), the display quality
can be improved by the application of the present invention, if a drop in the display
quality resulting from a current drop exists. Accordingly, the present invention is
not particularly limited to the matrix type as the structure of the display device.
[0108] In each embodiment of the present invention, the adjusting circuit has a positive
feedback circuit and it will be explained with reference to Figs. 40 to 42, hereunder.
[0109] Fig. 40 shows a part of the circuit construction of Fig. 1 and illustrating a positives
feedback circuit comprising operational amplifiers 102 and 103, used in the circuit
in Fig. 1.
[0110] Fig. 40 is modified from Fig. 1 in such a manner that the operational amplifiers
101 and 103 are converted into inverters 101 and 103 only taking each negative input
terminal thereof into account, in order to understand this easily.
[0111] In that, an output of the inverter 103 is applied to an one end terminal of an equivalent
capacity CT of the liquid crystal display panel through the common electrode driving
circuit 202 and another end terminal of the liquid crystal display panel is connected
to an input terminal of the inverter 101 through the segment electrode driving circuit
201.
[0112] While, an output terminal of the inverter 101 is connected to an input terminal of
the inverter 102 through a resister r.
[0113] As apparent from Fig. 40, it can be understood that the inverters 101 and 103 form
a positive feedback circuit through the capacity CT.
[0114] As the same way, it is apparent that the operational amplifier 102 and 103 provided
in the circuit as shown in Fig. 1 also form a positives feedback circuit through the
capacity CT of the liquid crystal.
[0115] Fig. 41 also explains the fact that the operational amplifiers 231 and 232 used in
the embodiment as shown in Fig. 29, form a positive feedback circuit. Fig. 41 is modified
from Fig. 29 in such a manner that the operational amplifiers 231 and 232 are converted
into inverters 231 and 232 only taking each negative input terminal thereof into account,
in order to get better understanding of this fact.
[0116] In that, an output of the inverter 232 is applied to an one end terminal of an equivalent
capacity CT of the liquid crystal display panel through the segment electrode driving
circuit 201 and another end terminal of the liquid crystal display panel is connected
to an input terminal of the inverter 231 through the common electrode driving circuit
202.
[0117] While, an output terminal of the inverter 231 is connected to an input terminal of
the inverter 232 through a resister R.
[0118] As apparent from Fig. 41, it can be understood that the inverters 231 and 232 form
a positive feedback circuit through the capacity CT.
[0119] As the same way, it is apparent that the operational amplifier 231 and 233 provided
in the circuit as shown in Fig. 29 also form a positive feedback circuit through the
capacity CT of the liquid crystal.
[0120] Fig. 42 also explains the fact that the operational an amplifier 271 used in the
embodiment as shown in Fig. 33, form a positive feedback circuit.
[0121] Fig. 42 is modified from Fig. 33 in such a manner that the operational amplifier
271 is converted into an amplifier 271 having only one input terminal only taking
positive input terminal thereof into account, in order to get better understanding
of this fact.
[0122] In that, an output of the amplifier 271 is applied to an one end terminal of an equivalent
capacity CT of the liquid crystal display panel through the segment electrode driving
circuit 201 and another end terminal of the liquid crystal display panel is connected
6o an input terminal of the amplifier 271 through a resister R and common electrode
driving circuit 202.
[0123] As apparent from Fig. 42, it can be understood that the amplifiar 271 forms a positive
feedback circuit through the capacity CT.
[0124] As the same way, it is apparent that the operational amplifier 271 provided in the
circuit as shown in Fig. 33 also form a positive feedback circuit through the:capacity
CT of the liquid crystal with respect to an output terminal VL.
1. An electrooptical display device comprising a display panel having common electrode
group and segment electrode group, a display device having a common electrode driving
circuit and a segment electrode driving circuit and an adjusting circuit provided
wiht a current detection means for detecting current flown through said display panel
and a voltage control means for controlling a driving voltage applied to both terminals
of the display panel and which is provided between a driving power source of said
display device and said display panel wherein said adjusting circuit operates so that
said voltage control means is operated in response to an output signal output from
said current detection means to correctly adjust a deformation of a wave-form of a
driving voltage applied to both terminals of said display panel.
2. An electooptical display device according to claim 1, wherein said adjusting circuit
includes a function to adjust said deformation of said wave-form by rapidly making
the driving voltage applied to both terminals of said display panel varied.
3. An electrooptical display device according to claim 1, wherein said adjusting circuit
includes a positive feedback function to rapidly increase a current flown into a load
of said display panel.
4. An electrooptical display device according to claim 1, wherein said positive feedback
function of said adjusting circuit can provide an operation to generate charge current
sufficient to fully charge a total capacitance of said display panel, mainly comprising
a plurality of liquid crystals, in a short time.
5. An electrooptical display device according to claim 1, wherein said current detection
means of said adjusting circuit is connected any one of said common electrode driving
circuit and said segment electrode driving circuit, while said voltage control means
thereof is connected to an opposite electrode driving circuit to which said current
detection means connects.
6. An electrooptical display device according to claim 1, wherein said current detection
means of said adjusting circuit is connected any one of said common electrode driving
circuit and said segment electrode driving circuit, while said voltage control means
thereof is connected to the same electrode driving circuit to which said current detection
means connects.
7. An electrooptical display device according to claim 1, wherein both of said current
detection means and said voltage control means of said adjusting circuit are connected
both of said common electrode driving circuit and:said segment electrode driving circuit.
8. An electrooptical display device according to claim 1, wherein said current detection
means of said adjusting circuit is connected any one of said common electrode driving
circuit and said segment electrode driving circuit, while said voltage control means
thereof is connected to both of said common electrode driving circuit and said segment
electrode driving circuit.
9. An electrooptical display device according to claim 1, wherein a voltage controlling
operation of said voltage control means of said adjusting circuit and current detecting
operation of said a current detection means thereof are not applied to a selected
common electrode in said common electrode group.
10. An electrooptical display device according to claim 1, wherein at least one of said
current detection means and said voltage control means of said adjusting circuit is
connected only to common electrodes not selected by said common electrode driving
circuit.
11. An electrooptical display device according to claim 1, wherein a plurality of segment
electrode driving voltage are applied to said segment electrode driving circuit from
a plurality of segment electrode driving voltage sources.
12. An electrooptical display device according to claim 11, wherein said adjusting circuit
is provided with a plurality of said voltaae control means or a plurality of said
current detection means each of which connected to said plurality of segment electrode
driving voltage sources, respectively.
13. An electrooptical display device according to claim 11, wherein said adjusting circuit
is provided with a current detection means connected to said common electrode driving
circuit and a plurality of segment electrode driving voltage control means connected
to said segment electrode driving circuit and to which a plurality of said segment
electrode driving voltage are applied, wherein each one of said segment electrode
driving voltage control means is controlled by an output signal output from said current
detection means.
14. An electrooptical display device according to claim 11, wherein said adjusting circuit
is provided with a common electrode voltage control means connected to said common
electrode driving circuit and a plurality of segment electrode driving current detection
means connected to said segment electrode driving circuit and to which a plurality
of said segment electrode driving voltage are applied, wherein said common electrode
voltage control means is controlled by each one of output signals output from said
each one of said current detection means.
15. An electrooptical display device according to claim 8, wherein both of said current
detection means and a first voltage control means of said adjusting circuit are connected
to any one of said common electrode driving circuit and segment electrode driving
circuit and said adjusting circuit is further provided with a second voltage control
means separate from said first voltage control means which is connected to an opposite
electrode driving circuit to which said first voltage control means connects.
16. An electrooptical display device according to claim 15, wherein said second voltage
control means is controlled by an output signal output from said current detection
means.
17. An electrooptical display device according to claim 1, wherein said current detection
means of said adjusting circuit comprises an operational amplifier and a current detection
resister provided at an output portion of said operational amplifier and said output
of said operational amplifier is connected to said voltage control means and fed back
to a negative input treminal of said operational amplifier through said current detection
resirter, wherein said negative input terminal of said operational amplifier being
connected to any one of said common electrode driving circuit and said segment electrode
driving circuit, while a positive input terminal of said operational amplifier is
set at a reference voltage level of any one of said common and segment electrode driving
voltage which is applied to any one of said common and segment electrode driving circuit
to which said negative input terminal of said operational amplifier connects.
18. An electrooptical display device according to claim 1, wherein said voltage control
means of said adjusting circuit comprises an operational amplifier an output terminal
of which connects to a negative input terminal thereof through a feed-back resister
and further connects to any one of said common electrode driving circuit and segment
electrode driving circuit, while a positive input terminal of said operational amplifier
is set at a reference voltage level of any one of said common and segment element
driving voltage supplied to any one of said common and segment electrode driving circuit
to which an output terminal of said operational amplifier connects, and said negative
input terminal thereof is set at a certain voltage level determined by processing
a predetetmined voltage set at said positive input terminal and a voltage cause and
varied by current flown into said display panel.
19. An electrooptical display device according to claim 14, wherein said adjusting circuit
comprises a first current detection means connected to one of said plurality of segment
electrode driving voltage source and detecting current flown through said segment
electrode driving circuit, a second current detection means connected to another one
of said segment electrode driving voltage source different from one to which said
first current detection means connects and detecting current flown through said segment
electrode driving circuit and a voltage control means connected to both of said first
and second current detection means and driving voltage source and further connected
to said common electrode driving circuit, wherein current detection means having the
same construction as defined by the claim 17 is used as said fist and second current
detection means while a voltage control means having the same construction as defined
by the claim 18 is used as said voltage control means and said device is further characterised
in that output of said first and second current detection means are input to said
negative input terminal of said voltage control means and each one of said reference
voltages of said plurality of segment electrode driving voltage sources being input
to said positive input terminal of said voltage control means.
20. An electrooptical display device according to claim 13, wherein said adjusting circuit
comprises a current detection means detecting current flown through said common electrode
driving circuit, a first voltage control means connected to one of said plurality
of segment electrode driving voltage source and a second voltage control means connected
to another one of said segment electrode driving voltage source different from one
to which said first voltage control means connects, wherein a current detection means
having the same construction:as defined by the claim 17 is used as said current detection
means while a plurality of voltage control means having the same construction as defined
by the claim 18 are used as said first and second voltage control means and said device
is further characterized in that an output of said current detection means is input
to said negative input terminal of said voltage control mean and each one of said
reference voltages of said plurality of segment electrode driving voltage source being
input to positive input terminals of said first and second voltage control means.
21. An electrooptical display device according to claim 6, wherein said adjusting circuit
comprises a circuit construction in which a current detection function for detecting
current flown through said common or segment electrode driving circuit is integrated
with a voltage controlling function for controlling a voltage of said common or segment
electrode to form one circuit and said adjusting circuit comprising operational amplifier
and wherein an output of said operational amplifier is connected to said common or
segment electrode driving circuit and fed backed to a negative input terminal thereof
while a positive input terminal thereof is set at a reference voltage level corresponding
to said common or segment electrode driving voltage at which said common or segment
electrode shold be set, and said adjusting circuit is further characterized in that
said output of said operational amplifier is positively fed back to said positive
input terminal thereof through a capacitance.
22. An electrooptical display device according to claim 21, wherein a resister is inserted
in said positive feed-back circuit.
23. An electrooptical display device according to claim 21, wherein said adjusting circuit
comprises said current detection means having a function for detecting current flown
through said common electrode driving circuit and said voltage control means for controlling
a voltage of said common electrode.
24. An electrooptical display device according to claim 14, wherein said adjusting circuit
comprises a first current detection means connected to one of said plurality of segment
electrode driving voltage source and detecting current flown through said segment
electrode driving circuit, a second current detection means connected to another one
of said segment electrode driving voltage source different from one to which said
first current detection means connects and detecting current flown through said segment
electrode driving circuit and a voltage control means connected to both of said first
and second current detection means and driving voltage source and further connected
to said common electrode driving circuit, wherein a current detection means having
the same construction as defined by the claim 21 is used as said first and second
current detection means while a voltage control means having the same construction
as defined by the claim 18 is used as said voltage control means and said device is
further characterized in that outputs of said first and second current detection means
are input to said negative input terminal of said voltage control means and each one
of said reference voltages of said plurality of segment electrode driving voltage
sources being input to said positive input terminal of said voltage control means.
25. An electrooptical display device according to claim 1, wherein said first and second
current detection means of said adjusting circuit is consisted only of a resister.
26. An electrooptical display device according to claim 25, wherein said resisters is
mounted on a substrate of said display panel.
27. An electrooptical display device according to claim 26, wherein said resisters of
both firs and second current detection means of said adjusting circuit are mounted
on a substrate of said display panel and said resister includes an inner resistance
of said display panel.
28. An electrooptical display device according to claim 17, wherein said current detection
resisters of said current detection means of said adjusting circuit are mounted on
a substrate of said display panel.
29. An electrooptical display device according to claim 28, wherein said current detection
resisters of said current detection means of said adjusting circuit are mounted on
a circuit substrate of said display panel and said resister includes an inner resistance
of said display panel.
30. An electrooptical display device according to claim 19, wherein each one of said first
and second current detection means of said adjusting circuit consists of coils and
a plurality of primary coils thereof connected between a reference voltage source
of said any one of said segment and common electrode driving voltage and any one of
said segment and common electrode driving circuits, while a plurality of secondary
coils thereof connected to said voltage control meams.
31. An electrooptical display device according to claim 1, wherein said current detection
means of said adjusting circuit has a function for detecting a total current flown
through overall said liquid crystal display panel while said voltage control means
ha a function for adjusting voltage variation of both maid common and segment electrode
driving voltages of said display panel.