BACKGROUND OF THE INVENTION
(a) Field of the Invention
[0001] The present invention relates to a plasma display, and a controller and driving method
thereof.
(b) Description of the Related Art
[0002] A plasma display uses a plasma display panel (PDP) that uses plasma generated by
a gas discharge process to display characters or images. The PDP includes, depending
on its size, more than several scores to millions of pixels arranged in a matrix pattern.
[0003] One frame time is 16.67ms (i.e. 1/60 second) in a national television system committee
(NTSC) method using a 60Hz frequency, and one frame time is 20ms (i.e., 1/50 second)
in a phase alternate line (PAL) method using a 50Hz frequency.
[0004] Since one frame time of 20ms is long enough so that a person may perceive an image
changing in the PAL method, the person may see the screen flickering every 20ms. That
is, a flicker phenomenon may occur in the PAL method.
[0005] To prevent the flickering effect, one frame is divided into first and second groups,
and subfields having greater weight values are separately applied to the two groups.
[0006] FIG. 1 shows a diagram representing subfield arrangement of one frame in the conventional
PAL method.
[0007] As shown in FIG. 1, one frame in the plasma display of the conventional PAL method
includes first and second groups, subfields SF1, SF3, SF5, and SF7 are applied to
the first group, and subfields SF2, SF4, SF6, and SF8 are applied to the second group.
That is, the first and second groups are respectively divided into the plurality of
subfields respectively having different luminance weight values, and the respective
subfields SF1 to SF8 include address periods A1 to A8 and sustain periods S1 to S8.
[0008] The address periods A1 to A8 are for selecting turn-on/off cells (i.e., cells to
be turned on or off) in a panel, and the sustain periods S1 to S8 are for causing
a discharge for displaying an image on the discharged cells. Here, lengths of the
sustain periods S1 to S8 correspond to weight values of the respective subfields SF1
to SF8, and it is assumed that that the lengths of the sustain periods S1 to S8 are
respectively 1T, 2T, 4T, 8T, 16T, 32T, 64T, and 128T. In addition, a reset period
(not shown) for initializing a discharge cell may be provided before the address periods
A1 to A8.
[0009] Here, a sum of weight values determines a grayscale of the discharge cell to be turned
on. As shown in FIG. 1, subfields SF1 to SF8 are arranged in increasing order of weight
or in decreasing order of weight.
[0010] In the PAL method shown in FIG. 1, a person may perceive a change of image every
10ms since the subfields having greater weight values are divided into two groups,
and therefore the flicker effect may be reduced.
[0011] Changes of luminance according to the arrangement of the subfields forming one frame
in the conventional PAL method shown in FIG. 1 are shown in FIG. 2.
[0012] FIG. 2 shows a diagram representing the changes of luminance in one frame in the
conventional PAL method.
[0013] In FIG. 2, a one-frame time is 20 ms, and 10ms is respectively applied to the first
and second groups. In the first and second groups, since subfields SF1, SF3, SF5,
and SF7 and subfields SF2, SF4, SF6, and SF8 are arranged from a low weight value
subfield to a high weight value subfield, the luminance is increased at latter subfields
of each group.
[0014] In FIG. 2A, subfields in the first and second groups are turned on. In addition,
the plasma display may express an image on the PDP by turning on subfield in one of
the first and second groups according to the grayscale of the image, which is shown
in FIG. 2A and B. That is, the subfield in the first group is turned on in FIG. 2B,
and the subfield in the second group is turned on in FIG. 2C.
[0015] FIG. 3 shows a diagram representing a relationship between a previous frame and a
subsequent frame of a frame that turns on the subfield in one of the two groups.
[0016] In FIG. 3A, the subfields in the first and second groups are turned on to express
an image in first and third frames as shown in FIG. 2A, and the subfield in the first
group is turned on to express the image in a second frame as shown in FIG. 2B. In
FIG. 3A, the subfields in the first and second groups are turned on to express an
image in the first and third frames, and the subfield in the first group is turned
on to express the image in the second frame as shown in FIG. 2C.
[0017] In FIG. 3A, since a sustain discharge is generated in the subfield of the first group
and it is not generated in the subfield of the second group in the second frame, misfiring
may be problematically generated in the first group of the subsequent third frame.
In FIG. 3B, a time delay in generating the sustain discharge is generated between
the second group of the previous first frame and the second group of the second frame
since the sustain discharge is not generated in the subfield of the first group of
the second frame, and therefore, the misfiring may be problematically generated in
the second group of the second frame.
[0018] The above information disclosed in this Background section is only for enhancement
of understanding of the background of the invention and therefore it may contain information
that does not form the prior art that is already known in this country to a person
of ordinary skilled in the art.
[0019] US 2005/0062690 discloses a method for driving a plasma display panel in which a plurality of subfields
is divided into first and second subfield groups of one frame and in which a start
time of the second subfield group changes according to a load ratio of an input video
signal. Similar methods are also disclosed in
US 2005/0073616,
EP 1 315 139 and
EP 1 450 338.
SUMMARY OF THE INVENTION
[0020] The present invention has been made in an effort to provide a plasma display for
preventing a misfiring operation, and a controller and driving method thereof.
[0021] According to an aspect of the invention, a driving method for sequentially driving
a plasma display by dividing a plurality of subfields of one frame into 2 groups of
subfields, wherein an on-subfield is defined as a subfield in which at least one cell
is lit on the whole screen comprises the method steps of:
- a) determining whether the first and the second group of subfields have on-subfields;
- b) if only the first group of subfields has at least one on-subfield, delaying the
turn-on time of the first group of subfields with respect to the beginning of the
frame while keeping the duration of the first group of subfields constant; and/or
- c) if only the second group of subfields has at least one on-subfield advancing the
turn-on time of the second group of subfields with respect to the beginning of the
frame while keeping the duration of the second group of subfields constant.
[0022] According to another aspect of the invention, a controller of a plasma display driven
by dividing a plurality of subfields of one frame into a first and a second subfield
group, is adapted to determine whether the first and the second group of subfields
of a frame have on-subfields. If only the first group of subfields has at least one
on-subfield, the controller is adapted to delay the turn-on time of the first group
of subfields with respect to the beginning of the frame while keeping the duration
of the first group of subfields constant. If only the second group of subfields has
at least one on- subfield, the controller is adapted to advance the turn-on time of
the second group of subfields with respect to the beginning of the frame while keeping
the duration of the second group of subfields constant.
[0023] According to yet another aspect of the invention, a plasma display comprises a plasma
display panel (PDP) comprising a first electrode, a second electrode, and a third
electrode in a direction crossing the first and second electrodes, the controller
of the invention and a driving circuit unit for driving the first to third electrodes
according to a controlling operation of the controller to change a turn-on time of
the group of subfields according to the subfield turn-on time control signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024]
FIG. 1 shows a diagram representing subfield arrangement of one frame in a conventional
PAL method.
FIGs. 2A to 2C show a diagram representing changes of luminance in one frame in the
conventional PAL method.
FIGs. 3A to 3B show a diagram representing a relationship between a previous frame
and a subsequent frame of a frame that turns on a subfield in one of two groups.
FIG. 4 shows a block diagram of a plasma display according to an exemplary embodiment
of the present invention.
FIG. 5 shows a block diagram representing a controller of a PDP according to the exemplary
embodiment of the present invention.
FIG. 6 shows a diagram representing grayscales when a subfield in a first group is
turned on.
FIG. 7 shows a diagram representing a subfield turn-on controlling operation of a
subfield location controller when a video signal having the grayscale shown in FIG.
6 is input.
FIG. 8 shows a table representing grayscales when the subfield in the second group
according to the exemplary embodiment of the present invention is turned on.
FIG. 9 shows a diagram representing a subfield turn-on controlling operation of a
subfield location controller when a video signal having the grayscale shown in FIG.
8 is input.
FIG. 10 shows a flowchart representing a subfield turn-on time controlling operation
of the controller according to the exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0025] In the following detailed description, only certain exemplary embodiments of the
present invention have been shown and described, simply by way of illustration. As
those skilled in the art would realize, the described embodiments may be modified
in various different ways, all without departing from the scope of the present invention.
Accordingly, the drawings and description are to be regarded as illustrative in nature
and not restrictive. Like reference numerals designate like elements throughout the
specification.
[0026] Throughout this specification and the claims which follow, when it is described that
an element is "coupled" to another element, the element may be "directly coupled"
to the other element or "electrically coupled" to the other element through a third
element.
[0027] In addition, wall charges mentioned in the following description mean charges formed
and accumulated on a wall (e.g., a dielectric layer) close to an electrode of a discharge
cell. A wall charge will be described as being "formed" or "accumulated" on the electrode,
although the wall charges do not actually touch the electrodes. Further, a wall voltage
means a potential difference formed on the wall of the discharge cell by the wall
charge. Throughout this specification and the claims which follow, unless explicitly
described to the contrary, the word "comprise", and variations such as "comprises"
or "comprising", will be understood to imply the inclusion of stated elements but
not the exclusion of any other elements.
[0028] A plasma display according to an exemplary embodiment of the present invention, and
a controller and a driving method thereof will now be described with reference to
the figures.
[0029] FIG. 4 shows a block diagram of the plasma display according to the exemplary embodiment
of the present invention.
[0030] As shown in FIG. 4, the plasma display according to the exemplary embodiment of the
present invention includes a plasma display panel (PDP) 100, a controller 200, an
address electrode driver 300, a scan electrode driver 400, and a sustain electrode
driver 500.
[0031] The PDP 100 includes a plurality of address electrodes A1 to Am extending in a column
direction, and a plurality of sustain and scan electrodes X1 to Xn and Y1 to Yn in
pairs extending in a row direction. The sustain electrodes X1-Xn are formed in respective
correspondence to the scan electrodes Y1 to Yn, and ends of the sustain electrodes
X1-Xn are connected in common. In addition, the PDP 100 includes a substrate (not
shown) having the sustain and scan electrodes X1-Xn and Y1 to Yn, and a substrate
(not shown) having the address electrodes A1-Am. The two substrates are arranged to
face each other with a discharge space between them so that the scan electrodes Y1
to Yn and the sustain electrodes X1-Xn may cross the address electrodes A1-Am. Here,
discharge spaces provided at crossing regions of the address electrodes and X and
Y electrodes form discharge cells. This formation of the plasma display panel 100
is an example, and another formation of a panel for applying driving waveforms that
will be described may be applied to the present invention.
[0032] The controller 200 receives external video signals, and outputs an address driving
control signal Sa, a sustain electrode driving control signal Sx, and a scan electrode
driving control signal Sy. In addition, the controller 200 divides a frame into a
plurality of subfields, and each subfield has a reset period, an address period, and
a sustain period in a temporal manner.
[0033] After receiving the address driving control signal Sa from the controller 200, the
address electrode driver 300 applies a display data signal for selecting discharge
cells to be displayed to the respective address electrodes A1-Am.
[0034] The scan electrode driver 400 receives the scan electrode driving control signal
Sy from the controller 200, and applies the driving voltage to the scan electrode
Y.
[0035] The sustain electrode driver 500 receives the sustain electrode driving control signal
Sx from the controller 200, and applies a driving voltage to the sustain electrode
X.
[0036] FIG. 5 shows a block diagram representing the controller of the PDP according to
the exemplary embodiment of the present invention.
[0037] As shown in FIG. 5, the controller 200 of the PDP according to the exemplary embodiment
of the present invention includes a subfield data generator 220 and a subfield location
controller 240.
[0038] The subfield data generator 220 transmits a control signal to the scan electrode
driver 400 and the sustain electrode driver 500 so that subfields SF1, SF3, SF5, and
SF7 in the first group and the subfields SF2, SF4, SF6, and SF8 are turned on according
to the grayscale for each frame.
[0039] The subfield data generator 220 transmits information of the turned on subfield to
the subfield location controller 240, receives a subfield turn-on timing control signal
generated by the subfield location controller 240, and transmits a control signal
for turning on the corresponding subfield to the scan electrode driver 400 and the
sustain electrode driver 500.
[0040] The subfield location controller 240 determines whether information on the plurality
of subfields received from the subfield data generator 220 includes the subfields
of the first and second group, or whether it includes the subfields SF1, SF3, SF5,
and SF7 or SF2, SF4, SF6, and SF8 of one of the two groups. According to a determined
result, the subfield location controller 240 generates the subfield turn-on timing
control signal for delaying a turn-on time of the subfield by a predetermined time
when the input information includes the subfield in the first group, and the subfield
location controller 240 generates the subfield turn-on timing control signal for advancing
the turn-on time of the subfield by the predetermined time when the information includes
the subfield in the second group, and transmits the subfield turn-on timing control
signals to the subfield data generator 220. In addition, when the received information
includes the subfields in the first and second groups, the subfield location controller
240 generates the subfield turn-on timing control signal, but there is no change in
the turn-on time of the subfield.
[0041] The turn-on time of the subfield that is controlled by the subfield location controller
240 shown in FIG. 5 will now be described with reference to FIG. 6 to FIG. 9.
[0042] FIG. 6 shows a diagram representing the grayscales when the subfield in the first
group is turned on, and FIG. 7 shows a diagram representing a subfield turn-on controlling
operation of the subfield location controller 240 when a video signal having the grayscale
shown in FIG. 6 is input.
[0043] The grayscales shown in FIG. 6 correspond to the second frame among the first and
third frames shown in FIG. 7, and it is assumed that the video signal having the dark-colored
grayscales 1, 4, 5, 16, 17, 20, and 21 are turned on in the second frame.
[0044] As shown in FIG. 7, the subfield data generator 220 informs the subfield location
controller 240 of the turned on subfields SF1, SF3, and SF5, and the subfield location
controller 240 delays the turn-on time of the subfield by the predetermined time since
the received information of the subfields includes the subfield in the first group.
[0045] FIG. 8 shows a table representing grayscales when the subfield in the second group
according to the exemplary embodiment of the present invention are turned on, and
FIG. 9 shows a diagram representing a subfield turn-on controlling operation of the
subfield location controller 240 when a video signal having the grayscale shown in
FIG. 8 is input.
[0046] The grayscales correspond to the second frame among the first and third frames shown
in FIG. 9, and video signals having dark-colored grayscales 2, 8, 10, 32, 34, 40,
and 42 are turned on in the second frame.
[0047] As shown in FIG. 9, the subfield data generator 220 informs the subfield location
controller 240 of the turned on subfields SF2, SF4, and SF6, and the subfield location
controller 240 advanced the turn-on time of the subfield by the predetermined time
since the received information of the subfields includes the subfields in the second
group.
[0048] FIG. 10 shows a flowchart representing a subfield turn-on time controlling operation
of the controller 200 according to the exemplary embodiment of the present invention.
[0049] Firstly, the subfield data generator 220 receiving the video signal initializes the
number N of frames in step S602. In this case, the number N of frames is exemplarily
initialized to be 1 in FIG. 10, but another natural number, a prime number, or a value
with a predetermined character (e.g. an alphabet) may be used. In addition, in step
S602, while the plasma display is turned on from a standby state, the controller 200
may perform the subfield turn-on time control operation from the first frame generated
by using the input video signal, and the subfield data generator 220 may perform an
initialization operation when the number of frames is increased to be higher than
a predetermined value since the video signal is continuously input.
[0050] The subfield data generator 220 performing the initialization operation in step S602
transmits a turn-on subfield value to the subfield location controller 240 according
to a grayscale to be expressed in a frame according to the video signal, and the subfield
location controller 240 determines in step S604 whether the subfield value includes
the subfield in the first group and the subfield in the second group.
[0051] When it is determined, according to a determined result in step S604, that the grayscale
of the corresponding frame is expressed by the subfield in one of the first and second
groups, the subfield location controller 240 determines in step S606 whether the received
subfield value includes the subfield in the first group.
[0052] When it is determined, according to a determined result in step S606, that the received
subfield value includes the subfield in the first group, the subfield location controller
240 generates the subfield turn-on time control signal for delaying the subfield turn-on
time by a predetermined time, and transmits it to the subfield data generator 220
in step S608. When it is determined that the received subfield value does not include
the subfield in the first group, the subfield location controller 240 determines that
it include the subfield value includes the subfield in the second group, generates
the subfield turn-on time control signal for advancing the subfield turn-on time by
the predetermined time, and transmits it to the subfield data generator 220 in step
S610.
[0053] In addition, in step S606, it may be established to determine whether the received
subfield value include the subfield in the second group, and in this case, the steps
S608 and S610 are changed from each other.
[0054] When it is determined, according to the determined result in step S604, that the
subfields in the first and second groups of the corresponding frame are turned on,
the subfield location controller 240 generates the subfield turn-on time control signal
for turning on the corresponding subfield without changing the turn-on time, and transmits
it to the subfield data generator 220. The subfield data generator 220 receiving the
subfield turn-on time control signal in step S604, S608, or S610 transmits a control
signal to the scan electrode driver 400 and the sustain electrode driver 500 so that
the corresponding subfield is turned on the controlled turn-on time in step S612.
[0055] The subfield data generator 220 determining the turn-on time of the corresponding
frame and transmitting the control signal in step S612, increases the number of frames
in step S614, and performs the step S604.
[0056] As described above, in a frame where subfields are divided into first and second
groups respectively having different weight values, the subfield in one of the first
and second groups is turned on. Accordingly, misfiring may be prevented, and the plasma
display may be stably driven.