U.S. patent number 3,893,018 [Application Number 05/426,968] was granted by the patent office on 1975-07-01 for compensated electronic voltage source.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Robert R. Marley.
United States Patent |
3,893,018 |
Marley |
July 1, 1975 |
Compensated electronic voltage source
Abstract
A voltage and temperature stable integrated voltage regulator
circuit offsets the negative temperature coefficient of the
base-to-emitter voltage of one transistor with a positive
temperature coefficient derived from the base-to-emitter voltage
differential .DELTA.V.sub.BE between a pair of additional
transistors. Other transistors are used to produce a pair of
regulated stable output voltages, each having a predetermined
voltage with respect to a different one of the two input voltage
terminals across which the regulator circuit is connected. Circuit
components are provided to cause the two output voltages to be
voltage and temperature stable or to have a predetermined
controllable temperature coefficient.
Inventors: |
Marley; Robert R. (Phoenix,
AZ) |
Assignee: |
Motorola, Inc. (Chicago,
IL)
|
Family
ID: |
23692925 |
Appl.
No.: |
05/426,968 |
Filed: |
December 20, 1973 |
Current U.S.
Class: |
323/313;
327/535 |
Current CPC
Class: |
G05F
3/30 (20130101) |
Current International
Class: |
G05F
3/08 (20060101); G05F 3/30 (20060101); G05f
005/00 () |
Field of
Search: |
;307/296,297
;323/1,4,8,16,19,22T,23 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Widlar, New Developments in IC Voltage Regulators, IEEE Journal of
Solid-State Circuits, Vol. SCHy 6, No. 1, Feb. 1971, pgs.
2-7..
|
Primary Examiner: Pellinen; A. D.
Attorney, Agent or Firm: Rauner; Vincent J. Jones, Jr.;
Maurice J.
Claims
I claim:
1. A voltage regulator circuit having first and second voltage
input terminals for connection across an unregulated direct current
voltage source including in combination:
first transistor circuit means coupled with said first and second
voltage input terminals and having an output terminal supplying a
voltage having a predetermined positive temperature
coefficient;
a shunt regulator transistor with emitter, base and collector
electrodes, the emitter thereof coupled with said second input
terminal and the base thereof coupled with the output terminal of
said first transistor circuit means;
first diode means;
first resistance means coupled with said first diode means at a
first junction in a series circuit, in the order named, between
said first input terminal and the output terminal of said first
transistor circuit means;
compensating means coupled between said first junction and the
collector of said shunt regulator transistor for offsetting
variations of the voltage across the base-emitter junction of said
shunt regulator transistor with variations in the voltage appearing
on said second input terminal; and
output circuit means including an output transistor having base,
collector and emitter electrodes, the base thereof coupled with the
collector of said shunt regulator transistor, the collector thereof
coupled with said first voltage input terminal and the emitter
thereof coupled with said second voltage input terminal.
2. The combination according to claim 1 wherein the emitter of said
output transistor is coupled with said second voltage input
terminal through at least a portion of said first transistor
circuit means, thereby comprising the coupling for said first
transistor circuit means with said first input terminal.
3. The combination according to claim 1 further including second
resistance means coupled with said first diode means in said series
circuit between said first junction and the base of said shunt
regulator transistor.
4. The combination according to claim 1 wherein said compensating
means comprises second diode means.
5. The combination according to claim 4 further including third
diode means coupled in series with said first diode means between
said first junction and the base of said shunt regulator
transistor, and wherein said first transistor circuit means causes
substantially equal current to flow through said first and third
diode means and said output transistor in said output circuit
means.
6. The combination according to claim 5 wherein said first, second
and third diode means and the base-emitter junctions of said shunt
regulator transistor and said output transistor all are connected
between said first and second input terminals in the forward
current conducting direction.
7. The combination according to claim 5 wherein said third diode
means comprises the base-emitter junction of a third transistor and
wherein a shunt resistance means is connected in parallel with said
base-emitter junction.
8. A voltage regulator circuit having first and second input
terminals for connection across an unregulated direct current
voltage source, including in combination:
first resistance means;
first and second transistor means, each having base, emitter, and
collector electrodes, with the collector-emitter path of said first
transistor, said first resistance means, and the collector-emitter
path of said second transistor coupled in the order named in series
circuit between said first and second input terminals, the base of
said second transistor coupled with the collector thereof;
second and third resistance means;
third, fourth and fifth transistor means, each having base,
collector, and emitter electrodes, with the collector-emitter paths
of said third transistor means and said fourth transistor means
coupled in series circuit with said third resistance means, the
collector-emitter path of said fifth transistor means and said
second resistance means, in the order named, between said first and
second voltage supply terminals, the base of said fifth transistor
means being coupled with the collector of said second transistor
means, and the base of said fourth transistor means being coupled
with its collector;
sixth and seventh transistor means, each having base, collector,
and emitter electrodes, with the collector-emitter paths of said
seventh and sixth transistor means connected in series circuit in
the order named between said first and second input terminals, the
bases of said third and seventh transistor means being coupled with
the collector of said seventh transistor means, the collector of
said sixth transistor means being coupled with the base of said
first transistor means, and the base of said sixth transistor means
being coupled with the collector of said fifth transistor means to
form a voltage regulator circuit having at least one output
terminal at the emitter of said first transistor.
9. The combination according to claim 8 further including a fourth
resistance means and an eighth transistor means having base,
collector, and emitter electrodes, with the collector thereof
coupled with said first input terminal, the emitter thereof coupled
with the collector of said first transistor means, and the base
thereof coupled with the collector of said third transistor means
and through said fourth resistance means to said first input
terminal, the resistance of said third and fourth resistance means
being equal and the junction of the emitter of said eighth
transistor means and the collector of said first transistor means
comprising a second output terminal for said regulator circuit.
10. The combination according to claim 8 wherein all of said
transistor means comprise NPN transistors and said second input
terminal is adapted to be coupled with a source of negative direct
current potential and said first input terminal is adapted to be
connected with ground potential.
11. The combination according to claim 10 wherein the emitter of
said second transistor is coupled directly to said second input
terminal and said fifth transistor has a total emitter area which
is greater than the emitter area of said second transistor, such
that the total collector-emitter current of said fifth transistor
passing through said second resistance means is equal to the
collector-emitter current of said second transistor, with said
fifth transistor operating at a lower current density than said
second transistor.
12. A voltage regulator circuit having first and second input
terminals adapted to be connected respectively to a point of
reference potential and an unregulated DC voltage source, including
in combination:
first resistance means;
first diode means;
a first transistor having base, collector, and emitter electrodes,
with the collector and emitter of said first transistor, said first
resistance, and said first diode means connected in a first series
circuit, in the order named, between said first input terminal and
said second input terminal;
second and third resistance means;
second and third transistors, each having base, collector, and
emitter electrodes, with the collector and emitter of said second
transistor, said third resistance means, the collector and emitter
of said third transistor, and said second resistance means
connected in a second series circuit, in the order named, between
said first and second input terminals, the base of said third
transistor being connected to the junction of said first resistance
means with said first diode means;
second diode means;
a fourth transistor having base, collector, and emitter electrodes,
said second diode means coupled in a third series circuit with the
collector and emitter of said fourth transistor, in the order
named, between said first and second input terminals, the collector
of said fourth transistor coupled with the base of said first
transistor, the base of said second transistor coupled with said
second diode means;
fourth resistance means coupled between the base of said fourth
transistor and said second input terminal; and
third diode means coupled between the collector of said third
transistor and the base of said fourth transistor.
13. The combination according to claim 12 further including a fifth
resistance means coupled across said third diode means; and a sixth
resistance means coupled between said second diode means and said
first input terminal.
14. The combination according to claim 13 wherein said first,
second and third diode means comprise fifth, sixth and seventh
transistors, respectively; with the emitter of said fifth
transistor being coupled to said second input terminal, and the
base and collector thereof being coupled to said first resistance
means; with the emitter of said sixth transistor being coupled to
the collector of said fourth transistor, and the collector and base
of said sixth transistor both being coupled with the base of said
second transistor and the collector of said seventh transistor;
with the base of said seventh transistor being coupled with the
collector of said third transistor, and the emitter of said seventh
transistor being coupled with the base of said fourth
transistor.
15. The combination according to claim 14 wherein the emitter of
said fifth transistor is coupled directly to said second input
terminal and said third transistor has a total emitter area which
is greater than the emitter area of said fifth transistor, such
that the total collector-emitter current of said third transistor
passing through said second resistance means is equal to the
collector-emitter current of said fifth transistor, with said third
transistor operating at a lower current density than said fifth
transistor.
16. The combination according to claim 14 wherein said fifth
resistance means coupled across the base and emitter electrodes of
said seventh transistor comprises a variable resistor.
17. The combination according to claim 14 wherein all of said
transistors are of the same conductivity type.
18. The combination according to claim 17 further including a sixth
resistance means coupled between said first input terminal and the
collector of said sixth transistor; seventh resistance means
coupled between the collector of said second transistor and said
first input terminal, said third and seventh resistance means
having the same value of resistance; and an eighth transistor
having collector, base and emitter electrodes, with the base
thereof coupled with the collector of said second transistor, the
collector thereof coupled with said first input terminal, and the
emitter thereof coupled with the collector of said first
transistor, a second output terminal being provided at the emitter
of said eighth transistor.
19. A voltage regulator circuit having first and second input
terminals for connection across an unregulated direct current
voltage source including in combination:
first resistance means;
first and second transistor means each having base, emitter and
collector electrodes, with the collector-emitter path of said first
transistor, said first resistance means and the collector-emitter
path of said second transistor coupled, in the order named, in
series circuit between said first and second input terminals, the
base of said second transistor means coupled with the collector
thereof;
second and third resistance means;
third and fourth transistor means each having base, collector and
emitter electrodes, with the collector-emitter path of said third
transistor means, said third resistance means, the collector
emitter path of said fourth transistor means, and said second
resistance means coupled in series circuit, in the order named,
between said first and second voltage supply terminals, the base of
said fourth transistor means being coupled with the collector of
said second transistor means;
fourth and fifth resistance means;
fifth transistor means having base, collector and emitter
electrodes, with the base thereof coupled with the collector of
said fourth transistor means, and said fourth and fifth resistance
means coupled in series circuit with the collector-emitter path of
said fifth transistor means, in the order named, between said first
and second input terminals, said first, second, third, fourth and
fifth transistor means all being of the same conductivity type;
and
sixth transistor means of a conductivity type opposite to the
conductivity type of said fifth transistor means and having base,
collector and emitter electrodes, the emitter of said sixth
transistor means coupled with the bases of said first and third
transistor means and coupled with a junction between said fourth
and fifth resistance means, the base coupled with the collector of
said fifth transistor means and the collector of said sixth
transistor means coupled with said second input terminal.
20. The combination according to claim 19 wherein said first,
second, third, fourth and fifth transistor means are NPN
transistors and said sixth transistor means is a PNP
transistor.
21. The combination according to claim 20 wherein said voltage
regulator circuit is fabricated as a monolithic integrated circuit
and said sixth transistor is a substrate PNP transistor.
22. The combination according to claim 20 further including a sixth
resistance means coupled between the collector of said second
transistor and said second input terminal and a seventh resistance
means coupled between the collector of said fourth transistor and
said second input terminal.
23. The combination according to claim 20 further including an
additional resistance means and a seventh NPN transistor having
base, collector and emitter electrodes, with the collector thereof
coupled with said first input terminal, the emitter thereof coupled
with the collector of said first transistor, and the base thereof
coupled with the collector of said third transistor and further
coupled through said additional resistance means to said first
input terminal.
24. The combination according to claim 23 wherein said third
resistance means and said additional resistance means have the same
value of resistance, and first and second output terminals for said
voltage regulator circuit are obtained at the emitters of said
first and seventh transistors, respectively.
Description
BACKGROUND OF THE INVENTION
A monolithic integrated circuit voltage regulator using only
transistors and capable of providing a zero temperature coefficient
regulated output voltage has been developed. Such a regulator is a
three terminal device and can be packaged in a standard three
terminal transistor power package.
A modification of this circuit has been made to produce two output
voltages of the type which are commonly required for emitter
coupled logic (ECL) transistor logic circuits. The two output
voltages required for such ECL circuits are used, respectively, to
supply a bias voltage (V.sub.BB) to the gates and to supply a bias
voltage (V.sub.CS) for the current source of the circuits. One of
these voltages, the current source bias voltage, generally is
established with reference to the negative supply voltage used with
such circuits. It has been found that when such a modified
regulator circuit is used to supply these bias voltages, the
current source bias voltage is subject to substantial variation
with variations in the unregulated negative supply voltage. This is
undesirable for ECL systems requiring a high degree of
regulation.
In addition, the known regulators used with ECL circuits do not
provide output voltages which track with temperature the
characteristics of the ECL circuits itself. Since the ECL circuit
exhibits a predetermined variation in characteristics with
temperature it is desirable for some applications that the circuit
providing the bias voltages also exhibits a matching or tracking
temperature characteristic to ensure that the operating
characteristics of the ECL circuits remain the same over a wide
ambient temperature range.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved voltage
regulator circuit.
It is another object of this invention to provide a voltage
regulator which produces an output voltage which is substantially
independent of supply voltage variations over a wide range of
temperature.
It is an additional object of this invention to generate two
regulated voltages with a voltage regulator circuit capable of
integrated circuit fabrication.
It is a further object of this invention to provide a voltage
regulator providing at least one output voltage which is
substantially independent of the variations of the supply voltage
applied to the regulator and which has a predetermined temperature
coefficient.
In accordance with a preferred embodiment of this invention, a
voltage regulator circuit has first and second voltage input
terminals which are adapted to be connected across an unregulated
direct current voltage source. A first transistorized circuit is
coupled with the first and second input terminals and has an output
terminal providing a voltage with a positive temperature
coefficient. A shunt regulator transistor has its base connected to
the output terminal of the first transistorized circuit. The
emitter of the shunt regulator transistor is coupled with the
second of the input terminal and its collector is connected through
compensating circuit to the first input terminal. The compensating
circuit offsets variations in the voltage across the base-emitter
junction of the shunt regulator transistor with variations in the
voltage appearing on the second input terminal. An emitter-follower
circuit includes an output transistor with its base coupled to the
collector of the shunt regulator transistor, its collector coupled
with the first input terminal and its emitter coupled with the
second input terminal by way of the first transistorized circuit.
The interconnections of the shunt regulator transistor and the
compensating circuit; in cooperation with the base-emitter junction
of the emitter-follower output transistor, operate in conjunction
with the first transistorized circuit to produce an output voltage
which is substantially independent of variations in the supply
voltage applied across the first and second input terminals and
which has a predetermined temperature coefficient.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram of a prior art circuit; and
FIGS. 2, 3 and 4 are circuit diagrams of preferred embodiments of
this invention illustrating different techniques for compensation
of voltage regulators.
DETAILED DESCRIPTION
Referring now to the drawings, in which the same or similar
components are identified by the same reference numerals throughout
the several figures, there is shown in FIG. 1 a prior art voltage
regulator circuit used as a bias driver for an ECL digital logic
system. For such systems, it is desirable to produce two regulated
output voltages which are identified in FIG. 1 as V1 and V2. The
voltage V1 is established with respect to ground or reference
potential and the voltage V2 is established with respect to a
negative direct current supply potential -V illustrated in FIG. 1.
The reference potential and negative supply potential -V are
applied respectively to a pair of input terminals 10 and 11 which
constitute the voltage input terminals for the circuit.
The lower portion of the circuit includes first and second NPN
transistors T1 and T2 interconnected to operate at different
current densities, so that a positive temperature coefficient of
the base-to-emitter voltage differential .DELTA.V.sub.BE is
produced between them. This is done by interconnecting the
collector and base of the transistor T1 to cause it to operate as a
diode, with its emitter connected directly to the -V input voltage
supply terminal 11. The different current densities are achieved by
connecting a resistor R2 between the emitter of the transistor T2
and the terminal 11, while the base of the transistor T2 is
connected directly to the collector of the transistor T1.
If the emitter areas of the transistors T1 and T2 were equal,
currents I(1) and I(2) flowing through these transistors
respectively would be such that the current I(2) would be less than
the current I(1). For reasons which will be more fully understood
subsequently, it is desirable for these two currents to be equal,
while still maintaining the positive temperature coefficient
base-to-emitter voltage differential .DELTA.V.sub.BE between the
transistors T1 and T2. To accomplish this, the total emitter area
of the transistor T2 is made larger than that of the transistor
diode T1. This is represented in FIG. 1 by showing the transistor
T2 as having a double or dual emitter. The exact ratio of the
emitter areas of the transistors T1 and T2 must be determined in
conjunction with the value of resistance of the resistor R2 to
arrive at the ratio which results in the relationship of
I(1)=I(2).
Since the transistors T1 and T2 are operated at different current
densities, the voltage drop across the resistor R2 is proportional
to the base-emitter voltage differential .DELTA.V.sub.BE. The
current gains of the transistors are chosen to be high; so that the
voltage drop across the collector resistor R1 of the transistor T2
also is proportional to .DELTA.V.sub.BE.
The current I(2) is supplied to the resistor R1 through the
collector-emitter path of a third NPN transistor T3 and a load
resistor R3, coupled to the input terminal 10. Similarly the
current I(1) for the transistor diode T1 is supplied through the
collector-emitter paths of a pair of NPN transistors T4 and T5 and
a resistor R4.
The collector of the transistor T2 is connected to the base of an
NPN shunt regulator transistor T6, which has its emitter connected
to the input terminal 11 and its collector connected through a load
resistor R5 to the terminal 10. The positive temperature
coefficient of the voltage applied from the collector of the
transistor T2 to the base of the transistor T6 is adjusted by the
adjustment of the differential current densities of the transistors
T1 and T2 to produce a voltage drop across the resistor R1, which,
when it is added to the voltage drop across the base-emitter
junction of the transistor T6, results in a voltage on the
collector of the transistor T6 which is proportional to the energy
band gap of the semiconductor material of the transistors. This
voltage has a zero temperature coefficient and is coupled to the
bases of the two emitter-follower transistors T3 and T5.
The emitters of the transistors T3 and T5 are coupled respectively
to the resistors R1 and R4 in the current paths supplying the
currents I(2) and I(1) to the transistors T2 and T1. The collector
of the transistor T3 also is connected to the base of the
transistor T4, which results in the reference voltage V1 being
expressed as:
V.sub.1 =.phi..sub.4 +R.sub.3 I.sub.(1) (1)
where .phi..sub.4 is the base-to-emitter voltage of the transistor
T4 and R.sub.3 I.sub.(1) is the voltage across R.sub.3. The
currents I.sub.(1) and I.sub.(2) are voltage independent due to the
nature of the circuit interconnections. Thus, the voltage V.sub.1
also is essentially voltage independent.
The current I(3), however, is produced by the shunt regulator
transistor T6 and varies significantly with any variations in the
negative voltage (-V) applied to the input terminal 11. Because of
the relatively large current variations in the current I(3)
resulting from the shunt regulator operation of the transistor T6,
the emitter-base forward voltage .phi.6 of the transistor T6 also
varies substantially. This term appears in the output voltage V2
supplied by the regulator circuit shown in FIG. 1. The voltage V2
may be derived as follows:
V.sub.2 =.phi..sub.6 +R.sub.1 I.sub.(2) +.phi..sub.3 -.phi..sub.5
(2)
where R.sub.1 I.sub.(2) is the voltage drop across the resistor R1,
.phi.3 is the emitter-base voltage of the transistor T3 and .phi.5
is the base-emitter voltage of the transistor T5.
The operating conditions of the circuit are established to cause
the currents I(1) and I(2) to be equal, so that .phi.3 equals
.phi.5 if the transistors T3 and T5 are matched. The equation then
can be expressed as:
V.sub.2 =.phi..sub.6 +R.sub.1 I.sub.(1) (3)
from the foregoing it can be seen that although the voltage V1 is
substantially independent of supply voltage variations, the voltage
V2 is not independent and varies significantly to the same extent
that the term .phi.6, the emitter-base forward voltage of the
transistor T6, varies with variations in the negative voltage
applied to the terminal 11. If both of the voltages V1 and V2 are
made substantially independent of temperature variations and supply
voltage variations, greater system noise immunity can be obtained
in computer systems which use such a bias driver circuit to supply
the operating potentials for the logic circuits, such as ECL logic,
of the system.
To overcome the deficiencies in the circuit illustrated in FIG. 1,
the circuits of FIG. 2 and FIG. 3 have been developed. The circuit
of FIG. 2 will be considered first, and so far as the components of
the circuit of FIG. 2 are the same as those of the circuit of FIG.
1, no additional description of those components will be made. The
voltage V1 in FIG. 2 is generated in the same manner as it is in
the circuit of FIG. 1. The voltage V2, however, in FIG. 2 is
developed from a modified circuit which includes a transistor diode
T7 connected in series between the emitter of the transistor T3 and
the resistor R1. In addition, a second transistor diode T8 is
connected in series between the lower terminal of the resistor R5
and the collector of the transistor T6. The base-collector junction
of the transistor diode T8 is connected to the base of the
transistor T3 to provide voltage drive for that transistor, while
the base of the transistor T5 continues to be connected to the
collector of the transistor T6. The addition of the two transistor
diodes T7 and T8 changes the relationship of the output voltage V2
in accordance with the following expression:
V.sub.2 =.phi..sub.6 +R.sub.1 I.sub.(2) +.phi..sub.7 +.phi..sub.3
-.phi..sub.8 -.phi..sub.5 (4)
where .phi..sub.7 is the emitter-base voltage of the transistor
T.sub.7, and .phi..sub.8 is the base-emitter voltage of the
transistor T.sub.8.
The transistor diode T7 is matched to the transistor T3 so that
both of these transistors have the same emitter-base voltage drop
across them. Thus .phi.3=.phi.7. As discussed in conjunction with
the development of the equations for the voltage V2 in conjunction
with FIG. 1, the currents I.sub.(1) and I.sub.(2) are selected to
be equal so that .phi.3=.phi.5. The transistor diode T8 is matched
to the transistor T6; so that .phi.8=.phi.6. In addition, the
transistors T4 and T5 are matched so that .phi.4 equals .phi.5. The
equation then can be expressed as:
V.sub.2 =R.sub.1 I.sub.(1) +.phi..sub.4. (5)
if in addition, R1 equals R3, then the equation for V2 is the same
as that for V1, namely:
V.sub.2 =R.sub.3 I.sub.(1) +.phi..sub.4. (6)
with the addition of the two transistor diodes T7 and T8, the
undesirable voltage dependent components have been removed from the
output voltage V2 and the two output voltages V1 and V2 are the
same but with reference to the two different input terminals 10 and
11 respectively.
One transistor base-emitter voltage term (.phi..sub.4) remains in
each of these output voltages because such a term is desirable in
ECL circuits to match the characteristics of the ECL circuits which
are supplied with these two bias voltages. The transistor diode T7
is required to produce sufficient voltage drop across R4 and the
transistor diode T1 to turn on the transistor T1 when the
transistor diode T8 is added to the circuit to cancel the effects
of the transistor T6.
Referring now to FIG. 3, there is shown another version of the
circuit for producing V2 with a controllable temperature tracking
rate or temperature coefficient for both of the output voltages V1
and V2. No additional description will be made of those circuit
components which already have been described.
FIG. 3 differs from FIG. 2 in that the transistor diode T7 has been
eliminated and is replaced with a transistor T9 having its
collector connected to the junction of the base of the transistor
T3 and the collector of the transistor diode T8. Its base is
connected to the collector of the transistor T2. The shunt
regulator transistor T6 no longer has its base connected directly
to the collector of the transistor T2, but the base of the
transistor T6 is connected to the junction of the emitter of the
transistor T9. A large value resistor R6 operates as a power supply
insensitive current source for the transistor T9, and a resistor R7
is connected across the base and emitter electrodes of the
transistor T9.
The transistor diode T8 of FIG. 3 operates to cancel out the
base-emitter voltage effects of the transistor T6 from the output
voltage V2 in the same manner as described above in conjunction
with FIG. 2. The circuit configuration of FIG. 3, however, operates
to enable a choice of a temperature tracking rate which varies from
a zero temperature coefficient to a negative temperature
coefficient of approximately -2.7 millivolts per degree centigrade
for the two output voltages V1 and V2 (at nominal output voltage of
1.3 volts). This provides the greatest flexibility for the circuit
in its utilization as a bias voltage driver circuit for logic
circuits which in turn may exhibit positive or negative
coefficients of temperature in their operation. It is desirable to
have the bias or regulator circuit track the circuits with which it
is used to minimize temperature effects.
The operation of the circuit of FIG. 3 is such that the transistor
combination of the transistors T1 and T2 continues to generate a
small voltage across the resistor R2 which has a positive
temperature coefficient due to the difference in the device current
densities of the transistors T1 and T2.
As stated previously, the gain ratio of the resistors R1 and R3
amplifies this voltage as it is needed for the circuit. Because the
resistor R6 and the emitter-base voltage .phi.6 of transistor T6
set the current of the transistor T9, the V.sub.BE voltage of the
transistor T9 is essentially just temperature dependent. The
resistor R7, which is connected across this V.sub.BE voltage thus
produces a current which has a negative temperature coefficient in
voltage across the resistor R1. By adjusting the relative values of
the resistors R1, R2, R7 and R3, the voltage across the resistors
R1 and R3 can be varied from a positive temperature coefficient to
a negative temperature coefficient and allows a wide variation of
temperature tracking rates for the circuit. This variation can be
effected in large part by making the resistor R7 a variable
resistor.
If it is desirable to have the output voltages V1 and V2 equal each
other, it is necessary that the resistors R1 and R3 are equal. If
V1 and V2 do not have to be equal, these resistors can have
different values. The development of the equations for the voltages
V1 and V2 for the circuit of FIG. 3 is accomplished in the same way
as the development which has been given above in conjunction with
the description of FIGS. 1 and 2.
In FIG. 4 there is shown another embodiment in which the
sensitivity of the shunt regulator transistor T6 to variations in
the supply voltage (-V) is compensated for without the addition of
the separate transistor diode T8 which is illustrated in FIGS. 2
and 3. In the circuit of FIG. 4, the collector of the transistor T2
is connected directly to the base of the shunt regulator transistor
T6 in the same manner as in FIG. 1. The collector of the shunt
regulator transistor T6, however, is not connected directly to the
resistor R5 but instead is connected to the base of a substrate PNP
transistor T10 and through a resistor R8 to the junction of the
emitter of the transistor T10 with the resistor R5. The collector
of the transistor T10 is connected directly to the voltage supply
terminal 11.
This configuration causes the PNP transistor T10 to shunt the
excess current flowing in the shunt regulator path and forces the
current in the transistor T6 to be substantially voltage
independent and only temperature dependent. This occurs since the
voltage across the resistor R8 is established by the emitter-base
voltage of the transistor T10 which is essentially a constant
voltage. The other portions of the circuit shown in FIG. 4 operate
in the same manner as in the discussion of the circuit shown in
FIG. 1.
If it is desired to cause the circuit of FIG. 4 to have something
other than a zero temperature coefficient, a pair of resistors R9
and R10 can be connected between the collectors of the transistors
T1 and T2, respectively, and the negative supply terminal 11. The
ratio of the values of the resistors R9 and R10 can be varied in
conjunction with the value of the resistor R1 to adjust the output
voltage produced by the circuit of FIG. 4 from one which has a
positive temperature coefficient to a negative temperature
coefficient over a wide variation of temperature tracking rates for
the circuit. Resistors R9 and R10 also can be varied in absolute
value to change the voltage levels at the outputs for V1 and V2. If
these features are not desired, the resistors R9 and R10 can be
eliminated and the circuit will operate substantially as a zero
temperature coefficient circuit.
The circuit of FIG. 4 does not require the additional diode
junction of the transistors T7 or T9 of FIGS. 2 and 3, so it is
capable of operation with a minimum supply voltage which is lower
by one V.sub.BE voltage drop than the circuits of FIGS. 2 and 3.
This is desirable for low voltage applications. The location of the
transistor T10 of the circuit of FIG. 4 results in excellent high
frequency roll-off, so that the tendency of the circuit to
oscillate is minimized. This would not be the case if a PNP
transistor current source were connected between the input terminal
10 and the collector of the transistor T6 in place of the resistor
R5.
The circuits illustrated in FIGS. 2, 3 and 4 which have been
described above, exhibit excellent insensitivity to variations in
the supply voltage (-V) applied to the input terminal 11 as opposed
to the circuit shown in FIG. 1. In addition, the circuits of FIGS.
3 and 4 permit the selection of a wide range of desired temperature
tracking rates between negative coefficients of temperature and
positive coefficients of temperature, while the circuits of FIGS. 2
and 4 are illustrative of a fully compensated bias drivers or
voltage regulator circuits.
The circuits of FIG. 2 and 3 use an offsetting diode to produce the
insensitivity of the circuit to variations in the supply voltage
(-V), while the circuit shown in FIG. 4 achieves this result by the
use of a current stabilizing technique. The net result on the
operation of the circuits is the same for both of these approaches
and it is the elimination of the problem of variations in the
supply voltage (-V) from affecting the output voltages produced by
the circuits.
* * * * *