US3310731A

US3310731A - Voltage reference circuit

Info

Publication number: US3310731A
Application number: US254772A
Authority: US
Inventors: Ostroff Arthur; D Agostino Michael
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1963-01-29
Filing date: 1963-01-29
Publication date: 1967-03-21
Anticipated expiration: 1984-03-21

Description

United States Patent 3,310,731 VOLTAGE REFERENCE CIRCUIT Arthur Ostrotl, Woodland Hills, Calif., and Michael DAgostino, Philadelphia, Pa., assignors to Radio Corporation of America, a corporation of Delaware Filed Jan. 29, 1963, Ser. No. 254,772 6 Claims. (Cl. 3234) This invention relates to voltage reference circuits which function to maintain the output voltage of the circuit equal to the input voltage of the circuit.

A volt-age reference circuit provides an output voltage which is substantially identical to some input reference voltage level and thec'ircuit tracks variations in the input reference voltage level to keep the output voltage substantially identical thereto. A voltage reference circuit may, for example, be utilized with a ferrite core memory which is subject to temperature changes. Although the voltage reference circuits illustrate-d herein are for such use, it may be used in other ways, as well.

In ferrite core memories, temperature changes tend to change the hysteresis loop characteristic of the ferrite cores in a manner which may cause erroneous switching of the ferrite cores when only half-select drive currents are applied to the cores. To prevent such errors, a temperature sensitive device, such as a thermistor, is mounted in the memory and connected in a manner to provide the input reference voltage level for the voltage reference circuit. The output of the voltage reference circuit faithfully tracks voltage changes in the thermistor network. This output voltage is applied to controlled circuits to vary the half-select memory drive currents in a manner to compensate for the temperature changes in the memory.

Since the drive currents vary appreciably in magnitude, dependent on the data being processed in the memory, the temperature variations therein, and because of the manner in which the reference voltage is applied to the controlled circuits, the voltage reference circuit should also function as a current sink circuit to absorb excess current applied to the output voltage terminal thereof.

Furthermore, the current variations should be absorbed by the voltage reference circuit without causing a change in the output voltage thereof.

Accordingly, it is an object of this invention to provide a new and an improved voltage reference circuit.

It is another object of this invention to provide a new and improved voltage reference circuit which functions as an efiicient current sink circuit.

A voltage reference circuit embodying the invention includes first and second transistors of opposite conductivity type but complementary to each other. A reference voltage source is coupled between the base and collector electrodes of said first transistor while the emitter electrode thereof is coupled to the base electrode of said second transistor.

A load is connected to the emitter of the second transistor so that the first and second transistors operate as a pair of cascaded emitter follower stages. The output voltage derived from across the load, and applied to the controlled circuits, is substantially equal to the voltage level of the reference voltage source and also track's voltage variations in the reference voltage source because of the emitter follower operation of the first and second transistors.

The voltage reference circuit functions as an eflicient current sink circuit by utilizing a third load transistor of the same conductivity type as the second transistor as the load on the second transistor and by providing a feedback path between the load and second transistors. The emitter-*to-collector current paths of the second and load transistors are serially connected together and the feed- 3,319,731 Patented Mar. 21, 1967 back path is provided by coupling the collector electrode of the second transistor to the base electrode of the load transistor. By these connections, the output voltage developed across the load transistor remains substantially the same as the input voltage even though appreciable variations occur in the current applied to the load transistor by the controlled circuits.

The novel features which are considered to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, 'both as to its organization and method of operation as Well as to additional objects and advantages thereof, will best be understood from the following description when read in conjunction with the accompanying drawing, in which:

FIGURE 1 is a schematic circuit diagramof a voltage reference circuit embodying the invention; and

FIGURE 2 is a schematic circuit diagram of a portion of another embodiment of the invention.

Referring now to FIGURE 1, a voltage reference circuit 10 embodying the invention includes a pair of transistors 11 and 12 of opposite conductivity type but complementary to each other. The transistors 11 and 12 comprise a pair of the emitter follower stages, coupled in cascade, to produce an output voltage which is substantially identical to the voltage exhibited by a reference voltage source 13. The first transistor 11, which is, for example, of the PNP conductivity type, includes base 14, emitter 15, and collector 16 electrodes. The reference voltage source 13, which is illustrated as being variable, is connected between the input base electrode 14 of the transistor 11 and a point of reference potential, or ground, in the circuit 10. The collector electrode 16 is connected directly to ground and thus the source 13 is connected directly across the base 14 and collector 16 electrodes of the transistor 11. The emitter electrode 15 of the transistor 11 is coupled through a load resistor 20 to a positive terminal 22 of a source of energizing potential, V By these connections, the transistor 11 is biased for linear operation in a common collector, or emitter follower, configuration.

The second transistor 12, which is of the NPN conductivity type and complementary to the first transistor 11 includes base 26, emitter 28 and collector 30 electrodes. The output emitter electrode 15 of the transistor 11 is coupled directly to the input base electrode 26 of the transistor 12. The collector electrode 30 of the transistor 12 is coupled through a resistor 32 to the positive potential terminal 22 of the source of energizing potential, V The emitter electrode 28 of the transistor 12 is coupled to a load transistor 34, which is a part of the load on the second emitter follower transistor 12.

The load transistor 34, which is of the NPN conductivity type, includes emitter 36, base 38, and collector 40 electrodes. The collector electrode 40 of the load transistor 34 is directly connected to the emitter electrode 28 of the second transistor 12. The emitter electrode 36 of the load transistor 34 is grounded. Thus, the emitterto-collector current paths of the second and load transistors 12 and 34 are serially connected together with the second transistor 12 operating as an emitter follower and the load transistor 34 functioning as the load thereon. A terminal 42 at the collector electrode 40 of the load tran sistor 34 provides an output terminal for the circuit 10. The output voltage developed from the terminal 42 to ground, or across the load transistor 34, is applied to control the controlled circuits 43. The base electrode 38 of 0 the transistor 34 is coupled through a resistor 44 to the to the negative potential terminal 46. The Zener diode,

in its reverse breakdown condition, maintains a substantially constant voltage difference between the collector electrode 30 of the transistor 12 and the base electrode 38 of the transistor 34. It is, of course, apparent that other coupling devices, such as a parallel resistor-capacitor combination could be utilized instead of the Zener diode 50, but the Zener diode t) exhibits a greater sensitivity in the feedback path.

The voltage sources V and V may, for example, comprise a single, grounded, center-tapped power supply with the terminal 22 being the above-ground positive terminal thereof and the terminal 46 being the below-ground negative terminal thereof.

In operation, the output voltage appearing at the output terminal 42 of the voltage reference circuit will be substantially equal to the voltage exhibited by the reference voltage source 13. Furthermore, the output voltage of the circuit 10 will closely follow in both direction and magnitude any variations in the voltage level exhibited by the reference voltage source 13. The emitter voltage of the first transistor 11 is equal to the voltage level of the reference voltage source 13 plus the small junction voltage of its forward biased emitter-base junction. The voltage appearing across the load transistor 34, or the emitter voltage of the transistor 12, is equal to the emitter voltage of the transistor 11 minus the small junction voltage across the forward biased emitter-base junction of the transistor 12. Since the transistors 11 and 12 are selected to be complementary, the emitter-base junction voltage of the transistor 11 is substantially equal and opposite to the emitter-base junction voltage of the second transistor 12, so they cancel each other. Thus, in quiescent operation, the output voltage of the voltage reference circuit 10 is identical to the voltage of the source 13.

If the reference voltage level from the source 13 changes, the emitter voltage of the transistor 11 changes in the same direction and substantially the same amount. This change in voltage is coupled directly to the base eleo trode 26 of the transistor 12 and causes the emitter voltage of the transistor 12 to similarly change in the same direction and substantially the same amount. Thus, the cascaded emitter follower transistors 11 and 12 produce an out-put voltage which is substantially identical to the reference voltage of the source 13 regardless of voltage variations in the source 13.

The second emitter follower transistor 12 and the load transistor 34 also function as an eflicient current sink by absorbing varying current-s applied to the output terminal 42 from the controlled circuits 43, and without causing the output voltage to vary from the reference level exhibited by the source 13. If the current input to the terminal 42 of the circuit 10 increases, the voltage from the output terminal 42 to ground, or across the load transis-tor 34, also tends to increase. The increase in positive voltage at the collector of the load transistor 34 tends to decrease the forward bias across the emitterbase junction of the NPN transistor 12 and reduces the current flowing through this transistor. The decreased current flow through transistor 12 tends to increase the current flow through Zener diode 50. The increased current through Zener diode is applied to the base electrode 38 of the load transistor 34. The increased base current of load transistor 34 causes the emitter base junction of the load transistor 34 to become more forwardly biased, causing an increased current fiow through the transistor 34 and a decreased impedance to be exhibited by this transistor. The output volt-age is therefore r 4. turned substantially to its initial value and the load transistor 34 absorbs the increased current input from the controlled circuits 43. An opposite sequence occurs, if the input current decreases.

The current from the energizing potential sources V and V remains substantially at its quiescent level. However, in the example described, a greater current flows through the Zener diode 50 and a reduced current flows through the emitter follower transistor 12. The sum of these two currents remiains substantially constant in the quiescent, transient, and steady state conditions of operation. Thus, the voltage reference circuit 10 functions as an efficient current sink while maintaining the output voltage at a particular reference level, regardless of significant changes in the input current.

With large current increases from the controlled circuit 43, the load transistor 34 of FIGURE 1 may tend to overload. In FIGURE 2 is shown a partial schematic circuit diagram of another embodiment of the invention adapted for longer current operation. In this embodiment of the invention a second load transistor 60 is cascaded in an emitter follower configuration with the first load transistor 34 to provide increased current gain to absorb larger input currents to the terminal 42. The second load transistor 60 includes a base electrode 62 which is coupled to the terminal 48 of the voltage reference circuit 10 of FIGURE 1, a collector electrode 64 which is directly coupled to the output terminal 42 of the circuit 10, and an emitter electrode 66 which is directly coupled to the base electrode 33 of the first load transistor 34. The embodiment of the invention shown in FIG- URE 2 operates in a similar manner to the embodiment of FIGURE 1 but due to an increased feedback, increased current gain enhances the current absorbing capability of the voltage reference circuit 10, without causing changes in the output voltage thereof. Additional stages of load transistors may be coupled to the load transistor 34, in the same manner as the load transistor 60, to handle larger currents from the controlled circuit 43.

It is to be noted that the embodiments of the invention disclosed in FIGURES 1 and 2 may be operated at a low current level from the sources V and V in the quiescent state. In the quiescent state, the voltage reference circuit 10 draws only enough current to place the emitter follower transistor 12 in a desirable region of operation. Furthermore, the current remains substantially constant during transient and steady state operating conditions, merely dividing differently through the Zener diode 59 and emitter follower transistor 12. An increase in current in one of these components is balanced by a substantially equivalent decrease in current in the other. Therefore, the circuit 10 exhibits a low level power consumption from the power supply V and V and the power supply need not be a high level power supply nor need it be well regulated. Thus, there is a considerable advantage over other known voltage reference circuits. Furthermore, should the circuit 10 be required to handle large current inputs from the controlled circuit 43, no change in the power supply is necessary. Additional load transistors may be added in tandem to the

load transistors

34 and 60 to absorb the larger current.

A voltage reference circuit 10, modified as illustrated in FIGURE 2, was constructed using the values and type of components shown in FIGURES 1 and 2. This circuit accommodated peak currents of 250 milliamperes with less than a 1% variation in output voltage.

What is claimed is: 1. An electrical circuit comprising in combination: a pair of transistors of the same conductivity type with each having base, emitter, and collector electrodes,

means for serially connecting together the emitter-tocollector current paths of said transistors so that one transistor functions as an emitter follower and the other functions as a load thereon,

biasing means for forward biasing the base electrode of each of said emitter follower and load transistors with respect to the emitter electrodes thereof, and

means for transmitting potential changes on said collector electrode of said emitter follower transistor to the base electrode of said load transistor including a direct current conductive device connected between said collector and base electrodes of said emitter follower and load transistors, respectively.

2. An electrical circuit in accordance with claim 1,

wherein said direct current conductive device comprises a Zener diode.

3. An electrical circuit comprising in combination:

a pair of transistors of the same conductivity type with each having base, emitter, and collector electrodes,

a source of energizing potential having opposite polarity terminals,

first and second resistors coupled from the collector and base electrodes, respectively, of said emitter follower transistor to one terminal of saidsource of energizing potential,

a third resistor coupled from the base electrode of said load transistor to the other terminal of said source of energizing potential,

means including said source of energizing potential for forward biasing the base electrodes of said pair of transistors with respect to the emitter electrodes thereof, and

means for transmitting potential changes on said collector electrode of said emitter follower transistor to said base electrode of said load transistor including a Zener diode coupled from the collector electrode of said emitter follower transistor to the base electrode of said load transistor,

said Zener diode being poled to conduct in a reverse direction from said collector to said base electrode to maintain a substantially constant voltage ditfer ence therebetween,

whereby current input variations to the collector electrode of said load transistor which tend to cause the collector voltage of said load transistor to vary cause current and voltage variations at the collector electrode of said emitter follower transistor which variations are coupled through said Zener diode to vary the base current of said load transistor in a direction to maintain the voltage at the collector electrode thereof substantially constant.

4. A voltage reference-current sink circuit comprising in combination:

first and second transistors with each having base, emitter, and collector electrodes,

means connecting said first and second transistors in a cascaded emitter follower configuration,

a voltage reference potential source coupled between the base and collector electrodes of said first transistor,

a load transistor having base, emitter, and collector electrodes,

means coupling said load transistor to said second transistor so that the emitter-to-collector current paths of said second and load transistors are serially connected, and

means providing a direct current conductive connection between the collector electrode of said second transistor and the base electrode of said load transistor.

5. A voltage reference-current sink circuit in accordance with claim 6, wherein said direct current conductive connection comprises a Zener diode poled to conduct in a reverse direction from said collector electrode of said second transistor to the base electrode of said load transistor.

6. A voltage reference-current sink circuit comprising in combination:

first and second transistors of opposite conductivity type with each having base, emitter, and collector electrodes,

means coupling the collector electrode of said first transistor to a point of reference potential in said circuit,

a reference voltage source coupled between the base electrode of said first transistor and said point of reference potential,

a source of energizing potential having opposite polarity terminals,

a resistor coupled from the emitter electrode of said first transistor to one terminal of said energizing source,

means coupling the base electrode of said second tran sistor to the emitter electrode of said first transistor,

a resistor coupled from the collector electrode of said second transistor to said one terminal of said energiZing source,

a load transistor having base, emitter, and collector electrodes,

means coupling the emitter electrode'of said load transistor to said point of reference potential,

means coupling the collector electrode of said load transistor to the emitter electrode of said second transistor so that said load transistor functions, as a load on said second transistor,

a resistor coupled from the base of said load transistor to the other terminal of said energizing source, and

a Zener diode coupled from the collector electrode of said second transistor to the base electrode of said load transistor,

said Zener diode being poled to conduct in a reverse direction in a breakdown condition thereof from the collector electrode of said second transistor to the base electrode of said other transistor.

References Cited by the Examiner UNITED STATES PATENTS 3,124,698 3/1964 Semmer 30751 3,174,095 3/1965 Cocker 32322 3,241,045 3/1966 Brosseau 32322 3,243,690 3/1966 Gately 32322 OTHER REFERENCES Hunter, L. P.: Handbook of Semiconductor Electronics, McGraw-Hill Book Co., Inc., N.Y., 1962, pp. 17-18.

JOHN F. COUCH, Primary Examiner.

K. D. MOORE, Assistant Examiner.

Claims

3. AN ELECTRICAL CIRCUIT COMPRISING IN COMBINATION: A PAIR OF TRANSISTORS OF THE SAME CONDUCTIVITY TYPE WITH EACH HAVING BASE, EMITTER, AND COLLECTOR ELECTRODES, MEANS FOR SERIALLY CONNECTING TOGETHER THE EMITTER-TOCOLLECTOR CURRENT PATHS OF SAID TRANSISTORS SO THAT ONE TRANSISTOR FUNCTIONS AS AN EMITTER FOLLOWER AND THE OTHER FUNCTIONS AS A LOAD THEREON, A SOURCE OF ENERGIZING POTENTIAL HAVING OPPOSITE POLARITY TERMINALS, FIRST AND SECOND RESISTORS COUPLED FROM THE COLLECTOR AND BASE ELECTRODES, RESPECTIVELY, OF SAID EMITTER FOLLOWER TRANSISTOR TO ONE TERMINAL OF SAID SOURCE OF ENERGIZING POTENTIAL, A THIRD RESISTOR COUPLED FROM THE BASE ELECTRODE OF SAID LOAD TRANSISTOR TO THE OTHER TERMINAL OF SAID SOURCE OF ENERGIZING POTENTIAL, MEANS INCLUDING SAID SOURCE OF ENERGIZING POTENTIAL FOR FORWARD BIASING THE BASE ELECTRODES OF SAID PAIR OF TRANSISTORS WITH RESPECT TO THE EMITTER ELECTRODES THEREOF, AND