BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] This invention relates to temperature-compensated Zener-diode voltage references.
More particularly, this invention relates to a so-called "auto-TC" voltage reference
wherein trimming of a circuit resistance to give a predetermined output voltage will
simultaneously optimize the temperature compensation for that output voltage.
2. Description of the Prior Art
[0002] One type of "auto-TC" voltage reference has been described in U.S. Patent 4,313,083.
There a Zener diode voltage is applied to one input terminal of an operational amplifier
and the other input terminal is supplied with a feedback voltage from a junction point
in a series circuit comprising a pair of transistors with a pair of trimmable resistors.
The bases of the two transistors are separately set to predetermined values by a three-resistor
voltage divider between the output line and ground. The circuit disclosed can provide
auto-TC compensation for Zener diodes having positive TC, but not for diodes having
negative TC.
[0003] EP-A-0 220 789 shows a Zener-diode circuit for use with CMOS processes where parasitic
bipolar transistors are produced as part of the CMOS process. Such bipolar-transistors
are formed in such a fashion that the circuit designer cannot make independent connections
to their collector. Thus, a special circuit arrangement is required.
[0004] The object of the present invention is to provide a temperature-compensated Zener-diode
voltage reference and a corresponding method which automatically produces zero TC
at the output voltage.
[0005] This object is achieved with the features of claims 1 and 9, respectively.
SUMMARY OF THE INVENTION
[0006] The present invention in one preferred embodiment provides an auto-TC voltage reference
wherein an operational amplifier receives at one input the voltage of a Zener diode
and at its other input receives a compensation signal from a feedback circuit comprising
a transistor and resistor network. When one of the resistors of the network is trimmed
to give a nominal output voltage for the reference, the TC of the reference voltage
will have been reduced to zero, or nearly so. The circuitry is capable of compensating
Zener diodes of either positive or negative TC.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007]
FIGURE 1 is a graph showing the temperature-response characteristics of Zener diodes
made by the same process;
FIGURE 2 is a schematic to illustrate the functioning of a voltage reference in accordance
with the invention;
FIGURE 3 shows a modified circuit based on Figure 2 but utilizing only a single transistor
in the feedback network;
FIGURE 4 presents a generalized schematic diagram to illustrate further aspects of
the invention;
FIGURE 5 is a circuit diagram showing a circuit design suitable for an integrated
circuit; and
FIGURE 6 is a circuit diagram showing a modification to the circuit of Figure 5.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0008] The graph of Figure 1 depicts in an idealized manner the temperature response characteristics
of the avalanche voltage (V
z) versus temperature of a group of Zener diodes produced by the same process. The
slopes of upper and lower solid lines 10 and 12 illustrate extremes of positive and
negative temperature coefficients (TC) respectively. Any one diode made by the process
can have a TC which lies anywhere between these extremes. It will be assumed in the
following discussion that the temperature response characteristic is linear, which
is approximately correct as a practical matter.
[0009] With Zener diodes made by the same process, it will be found that the temperature-response
characteristic lines for all diodes will (at least approximately) pass through the
same voltage point V
m at a temperature of T
m, as shown in Figure 1. T
m is shown as being negative on the absolute or Kelvin scale, which is generally true
in practice. Although such a negative T
m is not a realizable operating point, it is useful for analysis as an extrapolation
of Zener behavior in a normal operating temperature range.
[0010] It will be seen from Figure 1 that the avalanche voltage of the Zener diodes can
be described by:
where:
- Vz
- is the avalanche voltage,
- Vm
- is a voltage parameter which is relatively insensitive to variations in a given process
(and typically is in the range of 4.4V to 4.8V for a number of known processes),
- Tm
- is a temperature parameter which is relatively insensitive to variations in a given
process, and
- α1
- is a parameter with a value associated with each fabricated device. Its variability
from unit to unit encompasses most of the avalanche voltage variations which result
from process variability.
[0011] Referring now to Figure 2, there is shown a circuit for illustrating aspects of the
present invention. This circuit includes an operational amplifier 20 having its non-inverting
input terminal 22 connected to the positive electrode of a Zener diode 24 producing
a voltage V
z. The other Zener electrode is connected to a common line 26. The Zener voltage generally
is temperature sensitive, as discussed above with reference to Figure 1.
[0012] The output terminal 28 of the amplifier 20 produces an output voltage V
o responsive to the applied Zener voltage. A negative feedback circuit generally indicated
at 30 is connected between the output terminal 28 and the common line 26.
[0013] This feedback circuit 30 includes a number of series-connected elements comprising
a first segment 32 with a resistor R1 and diode D1, a second segment 34 with a resistor
R2 and a diode D2, and a resistor R3. The junction point 36 between the two segments
32, 34 is connected to the inverting input terminal 38 of the amplifier 20.
[0014] In considering the operation of this circuit, let it be assumed first that
, that R3 = 0, and that the diodes D1, D2 are matched. The voltage across the first
segment 32 (i.e., at the amplifier input terminal 38) will be essentially V
z, due to feedback action. Since R1 and R2 are equal, and carry equal currents, the
voltage V
x at the right-hand end of R2 (and at the output terminal 28) will be twice V
z. This relationship will hold true regardless of changes in temperature.
[0015] If the Zener diode 24 has a zero TC (rare, but possible), the output V
o will be temperature invariant. However, because there is a diode in each feedback
segment 32, 34, and because the V
BE of a diode has a negative TC, the current in the feedback circuit nevertheless will
vary with temperature.
[0016] With a Zener diode 24 having a negative TC (α
1 < 0), the voltage V
z at the amplifier input terminals 22 and 38 will decrease with increasing temperature
as will the output voltage V
o. Assuming that the V
BE of diode D1 has a TC which is more negative than the negative TC of V
z, the current through the feedback resistor R1 (and thus through R2) will have a positive
TC. This is because the temperature-induced negative change in V
BE of diode D1 with increasing temperature will be greater than the negative change
in Zener voltage V
z, so that the net voltage across R1 will increase with temperature, as will the current
through R1 (and R2).
[0017] If R3 now is made greater than zero (R3 > 0), the output V
o will increase due to the added voltage drop across R3 resulting from the feedback
current. This added increment to the output voltage will have a positive TC (since
the feedback current will in the circumstances noted above have a positive TC). By
adjusting the value of R3, the positive TC of the voltage across R3 can compensate
for the negative TC of the Zener voltage V
z, so that the output V
o can be made (essentially) invariant with temperature.
[0018] The same circuit can be used to provide similar compensation for Zeners with a positive
TC. In this case, rather than making R3 > 0, the value of R2 will be reduced. In effect,
R3 will be made "negative" (although of course a negative resistance is not actually
present in the circuit). The result will be that V
o is reduced (since the voltage drop across a reduced R2 is correspondingly reduced),
and the TC of the voltage across "negative" R3 will be negative, thus compensating
for the positive TC of the Zener.
[0019] The value of R3 thus can with advantage be viewed as an incremental deviation (±
R) from the nominal value of R2 where
. To provide for a practical trimming sequence, the initial value of R2 can be set
significantly less than R1 (R2 << R1), and R2 can be thought of as R2 "nominal" in
series with an initially negative R3 of relatively large value. The circuit without
any trimming should be capable of compensating for a limiting (maximum) positive TC
in the Zener 24. Since the actual Zener normally will have a less positive TC than
this limiting value, R2 can be trimmed up (increased in ohmic value) until the correct
magnitude is reached to provide compensation for the actual Zener involved (including
Zeners with negative TC).
[0020] The range of Zener TC which can be compensated is constrained by the relationship
between the diode V
BE and the magnitude of the Zener voltage V
z which determines the maximum TC of the current in R1 and R2. To increase this range,
more diodes can be added to both feedback segments 32, 34.
[0021] In determining the number of diodes in each feedback segment 32, 34, it may turn
out that the desired number of diode drops in each may not be an integer. Fractional
values of V
BE can be achieved and the circuit simplified (at least in the number of junctions required)
by using a "V
BE multiplier" of known configuration, as shown at 40 in Figure 3 (and also as described
in Brokaw Patent 4,622,512). The V
BE of transistor Q4 appears across resistor R6, and the accompanying current through
R6, R5 and R4 produces a multiplied version of that V
BE across resistors R5 and R4.
[0022] The feedback voltage for input terminal 38 is tapped off an intermediate point 36A
between R4 and R5. Thus the V
BE of one transistor can be "multiplied" to provide effective junction drops in both
feedback segments 32A and 34A.
Here the V
BE is effectively multiplied by (
), and this multiplied voltage is divided between the lower and upper segments in
proportions determined by the resistance values.
[0023] One limitation of the Figure 2 arrangement is that the output voltage V
o will always be at or near 2V
z. To accommodate a larger range of values for the output voltage, a modification as
illustrated in general form in Figure 4 can be employed. This configuration uses a
feedback circuit 30B where the elements in the second segment 34B have values "k"
times the values of the corresponding elements in the lower segment 32B (with k being
a preselected constant). Thus the diode drop in the upper segment is kV
c, and the series
resistor
. The output voltage then will be
, for the nominal case where α
1 = 0 and
. This Figure 4 relationship can be established in the Figure 3 feedback arrangement
by appropriately-sized feedback resistors.
[0024] By selection of circuit values, V
o can be made a convenient value higher than V
m. In the case of an auto-TC design (referred to above in the section on prior art
and as described in more detail below), the nominal value of V
o to which the output will be trimmed must be higher than the maximum anticipated Zener
voltage by an amount which allows for the temperature compensation voltage.
[0025] It may particularly be noted that for negative values of α
1, trimming to increase the output TC will increase the output voltage V
o. Conversely, for positive α
1, trimming to decrease the output TC (by making R2 < kR1) will lower the output voltage
V
o. Thus the direction of voltage change is correct for providing an auto-TC compensation.
To achieve that result, it is necessary to establish correct proportions between the
output voltage adjustment (change in V
o), and the induced TC.
[0026] Considering the auto-TC design further, the desired nominal output voltage V
o should first be chosen. This number can be somewhat arbitrary, but must be within
practical constraints. It must for example be comfortably higher than the nominal
Zener voltage V
m, and it must be within power supply voltage limitations. As an illustration, one
might select V
o = 6 volts. To provide a practical example, and with reference to the V
BE-multiplier arrangement of Figure 3, the feedback resistors in one circuit were as
follows:
R1 = 7K
R2 = 200 (initially)
R4 = 16.17K
R5 = 34.39K
R6 = 15K
[0027] Taking the case where the Zener diode produced a voltage V
m = 4.52V at a temperature T
m of -350°C (-78°K), and assuming that the Zener TC is a positive α
1 = 1 volt/°C, it was found that for the above simulated circuit a 6V output at 27°C
(room temperature) occurred when R2 was trimmed up to 694Ω. A subsequent temperature
sweep of 180° about room temperature (i.e., above and below room temperature) resulted
in a change in "Zener voltage" of about 360mV. The output voltage V
o changed only about 4 millivolts peak-to-peak, in a convex curve centered roughly
about 6 volts, with the output lower than 6V at both ends of the curve. For a simulated
Zener with a negative TC of -1/°C, a V
o of 6 volts at room temperature was obtained when R2 was trimmed to 4.56K. The output
changed by only about 5mV peak-to-peak over the same 180° temperature sweep, in a
curve which was inverted relative to the positive TC Zener curve.
[0028] In both cases, the value of R2 which made
also resulted in zero TC (or nearly so), thus providing the desired auto-TC feature.
Moreover, the circuit provided auto-TC for Zener diodes with either positive or negative
TC.
[0029] With regard to providing an auto-TC feature, it may be noted that R1 can be chosen
to give any nominal current through the feedback network at a given temperature. Since
V
c has a TC proportional to its value, the TC of the current can be adjusted by adjusting
V
C. Thus it is possible to independently choose the current and the TC of the current,
over some range. This is what makes it possible to find a single value of R3 which
compensates both the TC of V
o to zero (or nearly so) and simultaneously sets the output voltage at (1 + k)V
m.
[0030] To see what value of V
c will achieve this condition, first consider the case where the Zener has a voltage
V
m and zero TC. In this case, it will not be necessary to adjust R3 away from zero,
the feedback ratio will be (1 + k) at all temperatures, and both V
x and V
o will equal (1 + k)V
m.
[0031] If a Zener with a negative TC now is substituted so that the output V
o at room-temperature is lower, it will be necessary to increase R3 to bring V
o up to the desired (1 + k)V
m and to give it a zero TC, assuming that V
c has been chosen properly to give auto-TC. Then, at the trimming temperature, the
feedback ratio from the amplifier output will differ from 1 + k. As temperature changes,
the resulting change in proportions of resistor voltage to voltage source (diode drops)
in the feedback network will adjust the feedback ratio to keep V
o constant in the face of changing V
z.
[0032] If it is imagined that the temperature is changed to T
m (even though physically it might not be possible to do so), the voltage of the Zener
should change to V
m, since the characteristic temperature response lines of all Zeners pass through this
point (Figure 1). If R3 has been properly adjusted in the feedback, V
o should be at (1 + k)V
m at any temperature, including T
m. However, if R3 is not zero, the ratio of the resistive parts of the feedback would
not be (1 + k), although the voltage source component ratio always is.
[0033] The only way that these conditions can be satisfied simultaneously is if the current
in the feedback resistors is zero at the imagined condition where
, so that the resistors' contribution to the feedback voltage ratio is zero. This
requirement will be satisfied if
. This means that the temperature-response characteristic of V
c is a straight line (assuming linear relations) having a negative TC and passing through
the voltage V
m at temperature T
m. This is illustrated by the interrupted line 42 in Figure 1.
[0034] It is possible to construct a voltage source the behavior of which at circuit temperatures
extrapolates to this required behavior at T
m. First, it is noted that a transistor V
BE has a negative TC and its voltage extrapolates to go through the bandgap voltage
(approximately 1.2V) at 0°K. Choosing V
c to be a multiple of V
BE makes it possible to develop such a voltage which extrapolates to V
m at T
m. Using k times this multiple of V
BE as the voltage source in the upper segment 34B of the feedback completes the compensation
so that trimming R3 to bring V
o to (1 + k)V
m should also cause the TC of V
o to be zero.
[0035] In the Figure 3 configuration, the magnitude of V
c is set by the values of the resistors in the feedback network. In the example given
above, where V
m = 4.52V, it is necessary to select the resistors so that the value of V
c at room temperature will, when extrapolated back to T
m (assuming, as always in this analysis, linear relationships) be 4.52V. In the Figure
3 circuit, the value V
c = 4.52V will be represented by the voltage across R5 and R6 (it being noted that
at the temperature T
m with
there will be no current through any of the feedback resistors). The total voltage
across all three feedback resistors R4, R5 and R6 similarly will be 6V, since that
is the selected output voltage. Thus the resistance ratio
will be as follows:
It will be seen that the V
BE multiplier should produce a total of about 4 V
BEs, with one V
BE across R6, about two V
BEs across R5, and about one V
BE across R4.
[0036] Now considering the conditions at room temperature, with R2 adjusted to provide an
output V
o with zero TC at an output V
o of 6V, just as it was when the temperature was imagined to be at T
m, except that now current will be flowing through the feedback resistors. Since the
V
BE multiplier voltage ratio of the two segments 32A, 34A is to be the same at room temperature
as when at temperature T
m, the ratios of resistors R1 and R2 must conform to the previously determined ratio
of resistors R5 + R6 to R4 in order that the output be 6V. That is:
. If R1 is set at 7K for practical reasons, then R2 (nominal) will be about 2.3K,
for the nominal case when the Zener TC = 0. (Of course, the initial value of R2 will
be much less, say about 200Ω, in order that it can be trimmed in one direction to
cover all of the possible Zener characteristics from positive to negative TCs.)
[0037] Having determined the conditions for two operating points (
; T = room temperature) for an output of 6V with zero TC, it will be seen that the
output V
o must also be 6V, with zero TC, at all other operating points. This is because the
characteristics of all of the elements in the circuit have been assumed to be linear,
so that their summation or differencing must also be a linear relationship.
[0038] To provide a more detailed mathematical explanation of these relationships, the following
is presented with reference to Figure 4:
(where α
2 is the temperature coefficient of V
c)
[0039] The first term of this expression is the same as the nominal value of V
o for which the circuit is intended. To get V
o to the nominal value, R3 must be adjusted to make the remaining terms zero.
[0040] The temperature dependence can be divided out with the factor (T-T
m) to give:
[0041] This value of R3 should cause
(nominal) at all temperatures.
[0042] There are practical constraints however. V
c is not a battery, but something constructed of forward-biased diode drops. Therefore,
it must have some bias current to operate which implies that the voltage across R1
must be positive for all operating temperatures and bias conditions. Presumably T-T
m will always be positive, since T
m is often less than 0° Kelvin. Therefore the constraint that
requires that
or α
1 > α
2. Since it is desired to accommodate a range of α
1 which may be positive or negative, α
2 must be made more negative than the most negative value of α
1. That is, the TC of the compensating voltage must be more negative than the most
negative Zener TC expected from the process.
[0043] Another constraint arises from the nature of R3. In practice, R3 can be made large
by trimming R2 well beyond its nominal value
. It cannot be made more negative than the value of R2, however, since negative values
of R3 are realized in practice by leaving R2 trimmed below its nominal value. Therefore:
Substituting
in the expression for R3 gives:
Since R2 is always positive it may be divided out, and multiplying through by -1
will reverse the inequality and change the denominator to give:
Since
Since α
2 is negative, -α
2 will be positive, and assuming k is always positive
Since the denominator of the right side is positive, k will be constrained when α
1 is positive. For example, if the largest anticipated Zener TC
and
, then k > 1/3.
[0044] With reference to Figure 3, the base emitter voltage of the transistor will fall
more-or-less linearly with temperature according to the relation:
The largest component of this expression is the second term which is linear in T.
The third term usually reduces the effect of the fourth term, although the circuit
described here does not force a strictly PTAT collector current as is often done in
bandgap circuits.
[0045] Common practice, in uncorrected bandgap circuits, is to extrapolate V
BE back towards zero using a tangent to the curve at the center of the temperature range.
This results in a 0 Kelvin voltage slightly higher than V
GO, but the number is useful in a linearized approximation to behavior of V
BE vs. temperature.
[0046] In the auto-TC circuit disclosed herein, it is necessary to extrapolate the behavior
of V
BE back to T
m, the Zener temperature parameter. Using the design temperature value of V
BE and the TC at this temperature (or the slope inferred from V
BE and the 0 Kelvin extrapolation as otherwise determined), an extrapolated voltage
for V
BE at T
m can be calculated. Denoting this value V
E, the ratio of V
m to V
E will determine the "number" of V
BEs to be produced across R5 and R6. The value of R6 can be selected from biasing considerations
by determining how much of the total current in R1 can be diverted to R4, R5 and R6.
Then,
. This will cause the voltage across R5 and R6 to approximate the function
where α
2 is a multiple of the design temperature TC of V
BE. An error will result from the base current of the transistor Q4, but this will generally
be small. If low β is a problem, the error can be reduced by using an integral number
of diode connected transistors less than V
m/V
E, and multiplying only one to get any fractional part (see Figure 6).
[0047] The proper upper segment compensating voltage kV
c can be produced by making
, for the value of k selected to fit the design goals and previous constraints. Again
a mix of diodes and one multiplied V
BE can reduce base current error. Given the nominal V
BE and its multiplied value, the nominal voltage across R1 can be calculated based on
expected Zener voltage. This voltage together with the selected operating current
for the V
BE multiplier determines R1. The nominal value of R2 is kR1; however, the actual value
to use will depend on the expected negative values calculated for R3. Its trim range
will then depend on the positive values for R3.
[0048] The circuit also can be analyzed by holding R2 constant (R3 = 0). It will be found
from such analysis that the circuit can be trimmed by adjusting R1.
[0049] Figure 5 presents a detailed circuit diagram of a voltage reference in accordance
with this invention and suitable for adaptation to IC format. A dashed-line box 20
indicates the operational amplifier, as shown in the somewhat simplified diagrams
previously discussed. The feedback circuit 30A is of the V
BE-multiplier type described with reference to Figure 3. A start-up circuit 46 is provided
in the usual way.
[0050] Figure 6 presents a modified form of feedback circuit 30C for the voltage reference
of Figure 5, to reduce errors due to base current in the V
BE multiplier transistor Q4. In this modification a pair of diode-connected transistors
Q10 and Q11 have been connected in series with the transistor Q4 to produce the required
integral number of V
BEs, with the fractional part for the lower feedback segment being supplied by the V
BE multiplier across R5. Similarly, an additional transistor-connected diode Q5 has
been inserted between R4 and R2 with the fractional part of V
BE for the upper segment appearing across R4. The voltage between the network junction
point 36C and the top of R1 will be about 3-1/3 V
BEs. With this circuit the required extrapolated value for V
BE can be obtained with a smaller total resistance in the multiplier portion of the
circuitry (i.e., R4 and R5), so the base current of Q4 will flow through a smaller
resistance (R4), and thus cause less voltage error due to base current.
1. A temperature-compensated voltage reference for use with a class of Zener diodes made
by a single process, said voltage reference comprising:
an amplifier (20) having input means and an output circuit for producing a reference
voltage;
a Zener diode (24) of said class connected to said amplifier input means;
a feedback network (30) coupled to said output circuit;
said feedback network comprising first and second serial segments (32, 34), wherein
said second segment is connected to the output circuit of the amplifier,
said first and second segments (32, 34) respectively including first and second resistance
means;
means connecting an intermediate point between said serial segments (32, 34) to said
input means to furnish thereto a feedback signal representing the voltage across said
first voltage segment (32), said feedback signal being made to correspond to the Zener
diode voltage supplied to said input means;
means developing a temperature-responsive voltage having a negative temperature coefficient
being associated with said first segment to develop a temperature-responsive current
in said first segment having a positive temperature coefficient;
characterized by
said current flowing through said first segment (32) equally flowing through said
resistance means of said second segment (34) to produce a corresponding voltage drop
thereacross;
the magnitude of the voltage produced in said second segment (34) being predeterminedly
proportional to the magnitude of the voltage produced in said first segment (32);
the values of said first and second resistance means being set to effect temperature
compensation of that reference voltage to compensate for either a positive or a negative
temperature coefficient of the Zener diode voltage such that the current in said first
segment resistance means is in accordance with said Zener diode voltage and the temperature-responsive
voltage developed by said temperature responsive voltage means associated with said
first segment (32).
2. A temperature-compensated Zener-diode voltage reference as claimed in Claim 1, wherein
the temperature-responsive voltage means of said first segment (32) is sized to be
equal to said particular voltage level when extrapolated to said particular temperature.
3. A temperature-compensated Zener-diode voltage reference as claimed in Claim 1 or 2,
wherein the temperature-coefficient of said temperature-responsive means of said first
segment (32) is more negative than the most negative temperature coefficient expected
from said class of Zener diodes.
4. A temperature-compensated Zener-diode voltage reference as claimed in any of Claims
1 to 3, wherein said feedback network comprises a bipolar transistor (Q4) with a VBE multiplier circuit (40) so arranged that a first part of the total VBE voltage is effectively in said first segment (32) and a second part is effectively
in said second segment (34).
5. A temperature-compensated Zener-diode voltage reference as claimed in Claim 4, including
at least one series diode (Q10, Q11) connected in said first segment (32) to provide
for reduced resistances in said VBE multiplier circuit (40) so as to reduce errors due to the base current of said transistor
(Q4).
6. A temperature-compensated Zener-diode voltage reference as claimed in any of Claims
1 to 5 wherein the resistive element in said second segment (34) is trimmable to adjust
the reference voltage to a predetermined nominal level while optimizing the temperature
compensation of said reference voltage.
7. A temperature-compensated voltage reference as claimed in any of Claims 1 to 6, wherein
the nominal values of said second segment resistance and the voltage of the second
segment voltage-producing means are sized to be (1 + k) times the first segment resistance
and the voltage of the first segment voltage-producing means, where "k" is a preselected
constant.
8. A temperature-compensated Zener-diode voltage reference as claimed in any of claims
1 to 7, wherein the values of said first and second resistance means being set to
produce a predetermined nominal reference voltage.
9. The method of temperature-compensating the voltage of a Zener-diode comprising:
directing to the input means of an amplifier (20) a voltage derived from the Zener-diode
voltage, said amplifier having an output circuit producing a reference voltage; wherein
a feedback network (30) being coupled to said output circuit;
said feedback network comprising first and second serial segments (32, 34) wherein
said second segment is connected to the output circuit of the amplifier,
said first and second segments (32, 34) respectively including first and second resistance
means;
furnishing a feedback signal representing the voltage across said first voltage segment
(32) to said input means, wherein means connect an intermediate point between said
serial segments (32, 34) to said input means, said feedback signal being made to correspond
to the Zener-diode voltage supplied to said input means;
developing a temperature-responsive current in said first segment having a positive
temperature coefficient, wherein means developing a temperature-responsive voltage
having a negative temperature coefficient are associated with said first segment,
characterized by
producing a voltage drop corresponding to said current flowing through said first
segment (32) equally flowing through said resistance means of said second segment
(34),
setting the magnitude of the voltage produced in said second segment (34) to be predeterminedly
proportional to the magnitude of the voltage produced in said first segment (32);
setting the values of said first and second resistance means to effect temperature
compensation of that reference voltage to compensate for either a positive or a negative
temperature coefficient of the Zener-diode voltage such that the current in said first
segment resistance means is in accordance with said Zener-diode voltage and the temperature-responsive
voltage developed by said temperature responsive voltage means associated with said
first segment (32).
10. The method of temperature-compensating the voltage of a Zener diode as claimed in
Claim 9, including the step of trimming one of said resistance means to fix said output
voltage at a preselected level.
11. The method of temperature-compensating the voltage of a Zener diode as claimed in
Claim 10, including the step of trimming said one resistance means to produce a predetermined
output voltage level and simultaneously effect optimal temperature compensation of
that output voltage.
12. The method of temperature-compensating the voltage of a Zener diode as claimed in
Claim 10 or 11, wherein the resistance means in said second segment is trimmed to
produce said predetermined output voltage level.
13. The method of temperature-compensating the voltage of a Zener diode as claimed in
any of Claims 9 to 12, wherein said class of diodes have temperature-responsive voltage
characteristics all of which pass through a specific voltage at a specific temperature;
sizing the magnitude of said temperature-responsive voltage means in said first segment
(32) to a value which when extrapolated back to said specific temperature, will be
equal to said specific voltage.
14. The method of any of Claims 9 to 13 wherein said feedback current of said one segment
(32) is controlled to be proportional to the difference between said Zener diode voltage
and said first temperature-responsive voltage.
15. The method of any of Claims 9 to 14 wherein said negative feedback current is derived
at least substantially from said amplifier output circuit.
16. The method of any of claims 9 to 15 setting the values of said first and second resistance
means to produce a predetermined nominal reference voltage.
1. Temperaturkompensierte Spannungsreferenz zur Verwendung mit einer Klasse von Z-Dioden,
die in einem einzigen Prozeß hergestellt werden, wobei die Spannungsreferenz aufweist:
einen Verstärker (20) mit einer Eingangseinrichtung und einer Ausgangsschaltung zum
Erzeugen einer Referenzspannung;
eine Z-Diode (24) der Klasse, die mit der Verstärkereingangseinrichtung verbunden
ist;
eine Rückkopplungsschaltung (30), die mit der Ausgangsschaltung gekoppelt ist;
wobei die Rückkopplungsschaltung ein erstes und zweites serielles Segment (32, 34)
aufweist, wobei das zweite Segment mit der Ausgangsschaltung des Verstärkers verbunden
ist,
wobei das erste und zweite Segment (32, 34) eine erste bzw. zweite Widerstandseinrichtung
aufweist;
eine Einrichtung, die einen dazwischen liegenden Punkt zwischen den seriellen Segmenten
(32, 34) mit der Eingangseinrichtung verbindet, um an diese ein Rückkopplungssignal
zu übergeben, das die Spannung über dem ersten Spannungssegment (32) darstellt, wobei
bewirkt wird, daß das Rückkopplungssignal der Z-Diodenspannung entspricht, die an
die Eingangseinrichtung übergeben wird;
eine Einrichtung, die eine temperaturabhängige Spannung mit einem negativen Temperaturkoeffizienten
entwickelt und dem ersten Segment zugeordnet ist, um einen temperaturabhängigen Strom
in dem ersten Segment mit einem positiven Temperaturkoeffizienten zu entwickeln;
dadurch gekennzeichnet, daß
der Strom, der durch das erste Segment (32) fließt, gleichermaßen durch die Widerstandseinrichtung
des zweiten Segments (34) fließt, um einen entsprechenden Spannungsabfall über dieser
zu erzeugen;
die Größe der Spannung, die im zweiten Segment (34) erzeugt wird, vorbestimmt proportional
zur Größe der Spannung ist, die im ersten Segment (32) erzeugt wird;
die Werte der ersten und zweiten Widerstandseinrichtung eingestellt werden, um eine
Temperaturkompensation dieser Referenzspannung zu bewirken, um entweder einen positiven
oder einen negativen Temperaturkoeffizienten der Z-Diodenspannung zu kompensieren,
so daß der Strom in der Widerstandseinrichtung des ersten Segments der Z-Diodenspannung
und der temperaturabhängigen Spannung, die von der temperaturabhängigen Spannungseinrichtung
entwickelt wird, die dem ersten Segment (32) zugeordnet ist, entspricht.
2. Temperaturkompensierte Z-Diodenspannungsreferenz nach Anspruch 1, wobei die temperaturabhängige
Spannungseinrichtung des ersten Segments (32) so bemessen ist, daß sie dem bestimmten
Spannungspegel entspricht, wenn dieser bis zu der bestimmten Temperatur extrapoliert
worden ist.
3. Temperaturkompensierte Z-Diodenspannungsreferenz nach Anspruch 1 oder 2, wobei der
Temperaturkoeffizient der temperaturabhängigen Einrichtung des ersten Segments (32)
negativer ist als der von der Klasse von Z-Dioden erwartete negativste Temperaturkoeffizient.
4. Temperaturkompensierte Z-Diodenspannungsreferenz nach einem der Ansprüche 1 bis 3,
wobei die Rückkopplungsschaltung einen bipolaren Transistor (Q4) mit einer VBE-Multipliziererschaltung (40) aufweist, die so angeordnet ist, daß ein erster Teil
der VBE-Gesamtspannung effektiv in dem ersten Segment (32) und ein zweiter Teil effektiv
in dem zweiten Segment (34) ist.
5. Temperaturkompensierte Z-Diodenspannungsreferenz nach Anspruch 4, mit mindestens einer
reihengeschalteten Diode (Q10, Q11), die in dem ersten Segment (32) so verbunden ist,
daß für reduzierte Widerstände in der VBE-Multipliziererschaltung (40) gesorgt wird, um Fehler aufgrund des Basisstroms des
Transistors (Q4) zu reduzieren.
6. Temperaturkompensierte Z-Diodenspannungsreferenz nach einem der Ansprüche 1 bis 5,
wobei das Widerstandselement in dem zweiten Segment (34) abstimmbar ist, um die Referenzspannung
auf einen vorbestimmten Nennpegel einzustellen, wobei die Temperaturkompensation der
Referenzspannung optimiert wird.
7. Temperaturkompensierte Spannungsreferenz nach einem der Ansprüche 1 bis 6, wobei die
Nennwerte des Widerstands des zweiten Segments und der Spannung der Spannungserzeugungseinrichtung
des zweiten Segments so bemessen sind, daß sie das (1 + k)-fache des Widerstands des
ersten Segments und der Spannung der Spannungserzeugungseinrichtung des ersten Segments
betragen, wobei "k" eine vorgewählte Konstante ist.
8. Temperaturkompensierte Z-Diodenspannungsreferenz nach einem der Ansprüche 1 bis 7,
wobei die Werte der ersten und zweiten Widerstandseinrichtung eingestellt werden,
um eine vorbestimmte Nennreferenzspannung zu erzeugen.
9. Verfahren zur Temperaturkompensation der Spannung einer Z-Diode mit den Schritten:
Leiten einer Spannung, die von der Z-Diodenspannung abgeleitet ist, zur Eingangseinrichtung
des Verstärkers (20), wobei der Verstärker eine Ausgangsschaltung aufweist, die eine
Referenzspannüng erzeugt; wobei
eine Rückkopplungsschaltung (30), die mit der Ausgangsschaltung gekoppelt ist;
wobei die Rückkopplungsschaltung ein erstes und zweites serielles Segment (32, 34)
aufweist, wobei das zweite Segment mit der Ausgangsschaltung des Verstärkers verbunden
ist,
wobei das erste und zweite Segment (32, 34) eine erste bzw. zweite Widerstandseinrichtung
aufweisen;
Liefern eines Rückkopplungssignals, das die Spannung über dem ersten Spannungssegment
(32) darstellt, an die Eingangseinrichtung, wobei die Einrichtung einen dazwischen
liegenden Punkt zwischen den seriellen Segmenten (32, 34) mit der Eingangseinrichtung
verbindet, wobei bewirkt wird, daß das Rückkopplungssignal der Z-Diodenspannung entspricht,
die an die Eingangseinrichtung übergeben wird;
Entwickeln eines temperaturabhängigen Stroms in dem ersten Segment mit einem positiven
Temperaturkoeffizienten, wobei die Einrichtung, die eine temperaturabhängige Spannung
mit einem negativen Temperaturkoeffizienten entwickelt, dem ersten Segment zugeordnet
ist,
gekennzeichnet durch
Erzeugen eines Spannungsabfalis, der dem Strom entspricht, der durch das erste Segment
(32) fließt und der gleichermaßen durch die Widerstandseinrichtung des zweiten Segments
(34) fließt,
Einstellen der Größe der Spannung, die in dem zweiten Segment (34) erzeugt wird, so
daß sie vorbestimmt proportional der Größe der Spannung ist, die in dem ersten Segment
(32) erzeugt wird;
Einstellen des Wertes der ersten und zweiten Widerstandseinrichtung, um eine Temperaturkompensation
dieser Referenzspannung zu bewirken, um entweder einen positiven oder negativen Temperaturkoeffizienten
der Z-Diodenspannung zu kompensieren, so daß der Strom in der Widerstandseinrichtung
des ersten Segments der Z-Diodenspannung und der temperaturabhängigen Spannung, die
von der temperaturabhängigen Spannungseinrichtung entwickelt wird, die dem ersten
Segment (32) zugeordnet ist, entspricht.
10. Verfahren zur Temperaturkompensation der Spannung einer Z-Diode nach Anspruch 9, mit
dem Schritt des Abstimmens einer der Widerstandseinrichtungen, um die Ausgangsspannung
auf einen vorgewählten Pegel festzulegen.
11. Verfahren zur Temperaturkompensation der Spannung einer Z-Diode nach Anspruch 10,
mit dem Schritt des Abstimmens einer der Widerstandseinrichtungen, um einen vorbestimmten
Ausgangsspannungspegel zu erzeugen und gleichzeitig eine optimale Temperaturkompensation
dieser Ausgangsspannung zu bewirken.
12. Verfahren zur Temperaturkompensation der Spannung einer Z-Diode nach Anspruch 10 oder
11, wobei die Widerstandseinrichtung in dem zweiten Segment abgestimmt wird, um den
vorbestimmten Ausgangsspannungspegel zu erzeugen.
13. Verfahren zur Temperaturkompensation der Spannung einer Z-Diode nach einem der Ansprüche
9 bis 12, wobei die Diodenklasse temueraturabhängige Spannungskurven hat, die alle
bei einer spezifischen Temperatur durch eine spezifische Spannung laufen;
Bemessen der Größe der temperaturabhängigen Spannungseinrichtung in dem ersten Segment
(32) auf einen Wert, der, wenn er bis zu der spezifischen Temperatur zurückextrapoliert
wird, der spezifischen Spannung entspricht.
14. Verfahren nach einem der Ansprüche 9 bis 13, wobei der Rückkopplungsstrom des einen
Segments (32) so gesteuert wird, daß er proportional der Differenz zwischen der Z-Diodenspannung
und der ersten temperaturabhängigen Spannung ist.
15. Verfahren nach einem der Ansprüche 9 bis 14, wobei der negative Rückkopplungsstrom
zumindest wesentlich von der Verstärkerausgangsschaltung abgeleitet wird.
16. Verfahren nach einem der Ansprüche 9 bis 15, wobei die Werte der ersten und der zweiten
Widerstandseinrichtung eingestellt werden, um eine vorbestimmte Nennreferenzspannung
zu erzeugen.
1. Référence de tension compensée en température à utiliser avec une classe de diodes
Zener fabriquée par un seul processus, ladite référence de tension comprenant:
un amplificateur (20) ayant des moyens d'entrée et un circuit de sortie permettant
de produire une tension de référence;
une diode Zener (24) de ladite classe connectée auxdits moyens d'entrée de l'amplificateur;
un réseau de contre-réaction (30) couplé audit circuit de sortie;
ledit réseau de contre-réaction comprenant des premier et deuxième segments série
(32, 34), dans lequel ledit deuxième segment est connecté au circuit de sortie de
l'amplificateur;
lesdits premier et deuxième segments (32, 34) incluant respectivement des premier
et deuxième moyens de résistance;
des moyens connectant un point intermédiaire entre lesdits segments série (32, 34)
auxdits moyens d'entrée afin de fournir à ceux-ci un signal de contre-réaction représentant
la tension à travers ledit premier segment de tension (32), ledit signal de contre-réaction
étant fait pour correspondre à la tension de diode Zener fournie auxdits moyens d'entrée;
des moyens développant une tension sensible à la température ayant un coefficient
de température négatif associé audit premier segment afin de développer un courant
sensible à la température dans ledit premier segment ayant un coefficient de température
positif;
caractérisée par
ledit courant circulant à travers ledit premier segment (32) circulant également à
travers lesdits moyens de résistance dudit deuxième segment (34) afin de produire
une chute de tension correspondante à travers ceux-ci;
l'amplitude de la tension produite dans ledit deuxième segment (34) étant proportionnelle
de façon prédéterminée à l'amplitude de la tension produite dans ledit premier segment
(32);
les valeurs desdits premier et deuxième moyens de résistance étant fixées afin d'effectuer
une compensation en température de cette tension de référence afin de compenser un
coefficient de température soit positif soit négatif de la tension de diode Zener
de telle manière que le courant dans ledit moyen de résistance du premier segment
soit en accord avec ladite tension de diode Zener et la tension sensible à la température
développée par lesdits moyens de tension sensibles à la température associés audit
premier segment (32).
2. Référence de tension de diode Zener compensée en température selon la revendication
1, dans laquelle les moyens de tension sensibles à la température dudit premier segment
(32) sont calibrés pour être égaux audit niveau de tension particulier lorsqu'ils
sont extrapolés à ladite température particulière.
3. Référence de tension de diode Zener compensée en température selon la revendication
1 ou 2, dans laquelle le coefficient de température desdits moyens sensibles à la
température dudit premier segment (32) est plus négatif que le coefficient de température
le plus négatif prévu par ladite classe de diodes Zener.
4. Référence de tension de diode Zener compensée en température selon l'une quelconque
des revendications 1 à 3, dans laquelle ledit réseau de contre-réaction comprend un
transistor bipolaire (Q4) avec un circuit multiplieur de VBE (40) monté de telle manière qu'une première partie de la tension VBE totale soit effectivement dans ledit premier segment (32) et qu'une deuxième partie
soit effectivement dans ledit deuxième segment (34).
5. Référence de tension de diode Zener compensée en température selon la revendication
4, incluant au moins une diode série (Q10, Q11) montée dans ledit premier segment
(32) afin d'assurer des résistances réduites dans ledit circuit multiplieur de VBE (40) de manière à réduire les erreurs dues au courant de base dudit transistor (Q4).
6. Référence de tension de diode Zener compensée en température selon l'une quelconque
des revendications 1 à 5, dans laquelle l'élément résistif dans ledit deuxième segment
(34) est ajustable afin de régler la tension de référence à un niveau nominal prédéterminé
tout en optimisant la compensation en température de ladite tension de référence.
7. Référence de tension compensée en température selon l'une quelconque des revendications
1 à 6, dans laquelle les valeurs nominales de ladite résistance de deuxième segment
et de la tension des moyens produisant la tension du deuxième segment sont calibrées
pour être (1 + k) fois la résistance du premier segment et de la tension des moyens
produisant la tension du premier segment, où "k" est une constante présélectionnée.
8. Référence de tension de diode Zener compensée en température selon l'une quelconque
des revendications 1 à 7, dans laquelle les valeurs desdits premier et deuxième moyens
de résistance sont fixées afin de produire une tension de référence nominale prédéterminée.
9. Procédé de compensation en température de la tension d'une diode Zener comprenant:
l'orientation vers les moyens d'entrée d'un amplificateur (20) d'une tension dérivée
de la tension de diode Zener, ledit amplificateur ayant un circuit de sortie produisant
une tension de référence; dans lequel
un réseau de contre-réaction (30) étant relié audit circuit de sortie;
ledit réseau de contre-réaction comprenant des premier et deuxième segments série
(32, 34) dans lequel ledit deuxième segment est connecté au circuit de sortie de l'amplificateur,
lesdits premier et deuxième segments (32, 34) incluant respectivement des premier
et deuxième moyens de résistance;
la fourniture d'un signal de contre-réaction représentant la tension à travers ledit
premier segment de tension (32) auxdits moyens d'entrée, dans lequel des moyens connectent
un point intermédiaire entre lesdits segments série (32, 34) auxdits moyens d'entrée,
ledit signal de contre-réaction étant fait pour correspondre à la tension de diode
Zener fournie auxdits moyens d'entrée;
le développement d'un courant sensible à la température dans ledit premier segment
ayant un coefficient de température positif, dans lequel des moyens développant une
tension sensible à la température ayant un coefficient de température négatif sont
associés audit premier segment,
caractérisé par
la production d'une chute de tension correspondant audit courant circulant à travers
ledit premier segment (32) circulant également à travers ledit moyen de résistance
dudit deuxième segment (34),
la sélection de l'amplitude de la tension produite dans ledit deuxième segment (34)
pour qu'elle soit proportionnelle de manière prédéterminée à l'amplitude de la tension
produite dans ledit premier segment (32);
la détermination des valeurs desdits premier et deuxième moyens de résistance afin
d'effectuer la compensation en température de cette tension de référence afin de compenser
un coefficient de température soit positif soit négatif de la tension de diode Zener
de telle manière que le courant dans lesdits moyens de résistance du premier segment
soit en accord avec ladite tension de diode Zener et la tension sensible à la température
développée par lesdits moyens de tension sensibles à la température associés audit
premier segment (32).
10. Procédé de compensation en température de la tension d'une diode Zener selon la revendication
9, incluant l'étape consistant à ajuster un desdits moyens de résistance afin de fixer
ladite tension de sortie à un niveau présélectionné.
11. Procédé de compensation en température de la tension d'une diode Zener selon la revendication
10, incluant l'étape consistant à ajuster ce moyen de résistance afin de produire
un seuil de tension de sortie prédéterminé et d'effectuer simultanément une compensation
en température optimale de cette tension de sortie.
12. Procédé de compensation en température de la tension d'une diode Zener selon la revendication
10 ou 11, dans lequel le moyen de résistance dans ledit deuxième segment est ajusté
afin de produire ledit niveau de tension de sortie prédéterminé.
13. Procédé de compensation en température de la tension d'une diode Zener selon l'une
quelconque des revendications 9 à 12, dans lequel ladite classe de diodes a des caractéristiques
de tension sensibles à la température qui passent toutes par une tension spécifique
à une température spécifique; le calibrage de l'amplitude desdits moyens de tension
sensibles à la température dans ledit premier segment (32) à une valeur qui, quand
elle est extrapolée en arrière vers ladite température spécifique, sera égale à ladite
tension spécifique.
14. Procédé selon l'une quelconque des revendications 9 à 13, dans lequel ledit courant
de contre-réaction dudit premier segment (32) est commandé pour être proportionnel
à la différence entre ladite tension de diode Zener et ladite première tension sensible
à la température.
15. Procédé selon l'une quelconque des revendications 9 à 14, dans lequel ledit courant
de contre-réaction négatif est dérivé au moins notablement dudit circuit de sortie
de l'amplificateur.
16. Procédé selon l'une quelconque des revendications 9 à 15 fixant les valeurs desdits
premier et deuxième moyens de résistance afin de produire une tension de référence
nominale prédéterminée.