US3794861A

US3794861A - Reference voltage generator circuit

Info

Publication number: US3794861A
Application number: US00221731A
Authority: US
Inventors: J Bernacchi
Original assignee: Advanced Memory Systems Inc
Current assignee: Advanced Memory Systems Inc
Priority date: 1972-01-28
Filing date: 1972-01-28
Publication date: 1974-02-26
Anticipated expiration: 1991-02-26
Also published as: DE2260405A1; DE2260405B2

Abstract

A reference voltage generator circuit particularly suited for current source circuits having low temperature sensitivity and low voltage sensitivity. The circuit is comprised of a reference voltage circuit having low voltage sensitivity and relatively high temperature sensitivity, with an additional feedback circuit for feeding back a compensating temperature sensitivity to result in a low overall sensitivity. The temperature sensitivity of the reference generator is predominately due to the temperature sensitivity of a base to emitter diode voltage drop which may be selectively controlled or substantially cancelled by the proper selection of resistors in the feedback circuit so as to feed back a temperature sensitive component. The feedback signal is dependent upon the difference in the base to emitter voltage drops in two transistors conducting different magnitudes of current, and is similarly amplified so as to effectively allow cancellation of the basic reference generator sensitivity.

Description

United States Patent 1 Bernacchi REFERENCE VOLTAGE GENERATOR CIRCUIT [75] Inventor: Jerald Roy Bernacchi, Los Altos,

Calif.

[73] Assignee: Advanced Memory Systems, Inc.,

Sunnyvale, Calif.

22 Filed: Jan. 28, 1972 211 Appl. No.: 221,731

[ Feb. 26, 1974 3,286,151 11/1966 Dinger 307/297 Primary Examiner-Rudolph V. Rolinec Assistant ExaminerRo. E. Hart Attorney, Agent, or Firm-Spensley, Horn & Lubitz [57] ABSTRACT A reference voltage generator circuit particularly suited for current source circuits having low temperature sensitivity and low voltage sensitivity. The circuit is comprised of a reference voltage circuit having low voltage sensitivity and relatively high temperature sensitivity, with an additional feedback circuit for feeding back a compensating temperature sensitivity to result in a low overall sensitivity. The temperature sensitivity of the reference generator is predominately due to the temperature sensitivity of a base to emitter diode voltage drop which may be selectively controlled or substantially cancelled by the proper selection of resistors in the feedback circuit so as to feed back a temperature sensitive component. The feedback signal is dependent upon the difference in the base to emitter voltage drops in two transistors conducting different magnitudes of current, and is similarly amplified so as to effectively allow cancellation of the basic reference generator sensitivity.

11 Claims, 2 Drawing Figures 3,519,842 7/1970 Furuishi 307/297 3,421,102 1/1969 Andrews 307/297 3,659,121 4/1972 Frederiksen 307/297 3,401,274 9/1968 Marsh 307/297 3,643,151 2/1972 Matsushima 317/33 V R 3,657,572 4/1972 Millman 307/297 3,320,439 5/1967 Widlar 307/297 3,402,303 9/1968 Painter 307/297 '20 VEE PAIENIEDrmsmM V. REF

V. REF

l REFERENCE VOLTAGE GENERATOR CIRCUIT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of reference voltage circuits, and particularly to reference voltage circuits for current source bipolar integrated circuits.

2. Prior Art Electronic voltage regulators of various designs are well known in the prior art. However, most of such regulators are not adapted for integrated circuit fabrication, at least not in an entirely integrated form. There is, however, a need for such regulators which are substantially power supply voltage insensitive and which may be designed to achieve a predetermined temperature sensitivity. By way of example, the use of current source emitter coupled logic (ECL) design principles has become popular in recent years for the fabrication of bipolar integrated circuits. The use of these techniques permits the circuit designer significantly greater design freedom by allowing him to utilize a larger percentage of the power supply bias for switching applications. The work current source, as used hereabove, is used in the general sense and is meant to include current sources and sinks. By way of example, a typical current sink may be comprised of an NPN transistor with the collector being the current sink connection, the emitter being coupled to the negative power supply line through a fixed resistor, and the base coupled to a reference voltage, e.g., a fixed voltage with respect to the negative terminal. Thus, the current value of the current sink is equal to the reference voltage minus the base to emitter voltage, all divided by the value of the fixed resistor. Consequently, it is apparent that if a power supply voltage insensitive and temperature insensitive current sink is desired, the reference voltage must be substantially independent of power supply voltage and vary approximately in accordance with one base to emitter voltage temperature variation.

One prior art reference circuit which exhibits a relatively low temperature sensitivity is comprised of a pair of transistors and a pair of resistors. The first transistor has its collector coupled to one power supply terminal through one of the resistors and its emitter coupled through the other supply terminal through the second resistor. Thus by supplying an adequate base current to this transistor, the collector voltage of the transistor will be determined primarily by the values of the two resistors. The second transistor has its collector coupled to one power supply terminal, its base coupled to the collector of the first transistor, and its emitter coupled to the base of the first transistor and further to the reference voltage terminal so as to provide the output voltage and current. This circuit is relatively temperature insensitive since the base to emitter diode drops effecting the output reference voltage are generally small compared to the power supply voltage. However, as previously indicated, the reference voltage is basically determined by the collector voltage of the first transistor, which is basically proportional to the power supply voltage. Consequently, the reference voltage generated by such circuits is highly power supply voltage dependent, and therefore may only be used in circuits when the power supply voltage will be maintained within reasonably narrow limits.

Another type of prior art reference generator circuit uses the base to emitter voltage of a first transistor as a reference voltage, which is amplified in proportion so as to provide the desired fixed reference. The base emitter voltage of a transistor is relatively power supply voltage independent, and therefore such circuits may operate over a wide input voltage range. However, the base to emitter voltage is highly temperature dependent, and therefore the power supply voltage insensitivity is achieved at the expense of temperature range capability.

It should be noted also that while a substantially power supply voltage insensitive, temperature insensitive reference voltage is desired, the circuits which utilize such reference voltages will themselves often ex-- hibit certain temperature characteristics, and therefore may more desirably perform if the reference voltage is made temperature sensitive in a predetermined man ner. By way of example, it may be desired to provide a reference voltage which varies with temperature in a predetermined and controlled manner so as to provide a reference voltage which more properly matches the circuit requirement, considering temperature induced changes in the values of resistors, diode voltage drops, etc. Therefore, there is a need for a power supply voltage insensitive reference generator which is substantially temperature insensitive, and more preferably may be caused to have a predetermined temperature sensitivity to match the circuit requirements for the circuits connected thereto.

BRIEF SUMMARY OF THE INVENTION A reference voltage generator circuit particularly suited for current sourced circuits having low temperature sensitivity and low power supply voltage sensitivity. The circuit is comprised of a reference voltage circuit having low voltage sensitivity and relatively high temperature sensitivity, with an additional feedback circuit for feeding back a compensating temperature sensitivity to result in a low overall sensitivity. The temperature sensitivity of the reference generator is predominately due to the temperature sensitivity of a base to emitter diode voltage drop, which may be selectively controlled or substantially cancelled by the proper selectionof resistors in the feedback circuit so as to feed back a predetermined temperature sensitive component. The primary factor determining the reference voltage output of the circuit is the base emitter diode drop in a particular transistor, which is multiplied by a ratio of resistors selected so as to achieve the basic desired reference voltage. The feedback signal is dependent upon the difference in the base to emitter voltage drop in two transistors conducting different magnitudes of current, and is amplified by a second ratio of resistors so as to allow the control or cancellation of the basic reference generator sensitivity, dependent upon the selection of various resistors used in the circuit. Consequently, by maintaining a predetermined ratio of resistors, as may be easily achieved in integrated circuit fabrication, the desired temperature sensitivity of the reference voltage generated thereby may be achieved. The circuit of the present invention exhibits no primary power supply voltage dependence, the power supply voltage only indirectly effecting the reference voltage generated thereby as a result of the net change in base to emitter voltage drops caused by a change of current through the various transistors in response to the power supply voltage variation.

BRIEF DESCRIPTION OF THE DRAWINGS ment for the reference voltage generator of the present.

invention.

DETAILED DESCRIPTION OF THE INVENTION First referring to FIG. 1, a schematic diagram for typical current sources for current sourced bipolar circuits may be seen. (The word source" as used herein is used in the general sense to indicate both sources and sinks, the circuit shown in FIG. 1 perhaps more specifically representing typical current sinks.) Each current source is comprised of a transistor with a resistor in the emitter circuit. A reference voltage is applied between

terminals

20 and 22, with terminal 22 being connected to the bases of the transistors in each current source, such as transistors 06 and Q7. Each of the transistors Q6 and Q7 have resistors R6 and R7 respectively coupled between their emitters and terminal 20. The collectors of each transistor provide the current source connection for the remaining circuitry in which the current sources are used (not shown). It may be seen that the voltage across each resistor is equal to the voltage on terminal 22 (VREF) minus the base to emitter voltage drop in the associated transistor (VBE). The

current in each resistor is equal to (VREF VBE)/R where R is the value of the particular resistor. The base current of each transistor is generally relatively small, and therefore the collector current will be. approximately equal to the emitter current. Consequently, by way of example, the collector current of the first current source [6 equals (VREF VBE6)/-R6.

It is thus apparent that the current generated as. a re-' sult of the reference voltage applied to terminal 22 is a function of the emitter resistor of a particular current source and is also highly dependent upon the reference voltage applied to the current. Furthermore, in terms of variation'with temperature, it is apparent that the current will. change substantially with changes in the resistors with temperature and with changes in the base to emitter voltage drop in the transistor.

Now referring to FIG. 2 the circuit of the preferred embodiment of the present invention may be seen. The circuit is basically a three terminal circuit, with'terminal 20 being connected to the low voltage power supply terminal VEE, which for purposes of reference will be assumed to be ground. This terminal also provides one connection to thecurrent sources, and therefore is identified with the same numeral as the equivalent terminal in FIG. 1. Similarly, terminal 22 is the output terminal for the reference generator of the present invention and is identified in common with the VREF terminal of the circuit of FIG. 1. Terminal 24 is connected to the positive power supply terminal and is maintained at a voltage identified as VCC.

In the explanation and .analysis of the circuit to follow, it is assumedthat the base current of each of the transistors is small in comparison to the emitter and collector currents and therefore base currents are neglected and the collector and emitter currents of each Resistor R2 is coupled between the base and the emitter of transistor 01, and therefore the voltage across the resistor R2 is equal to the base to emitter diode voltage of transistor Q1. The current 12 in resistor R2 is therefore VBEQl/R2. Neglecting for the moment the current I4, the current ll in resistor R1 connected between the emitter of transistor Q2 and the base of transistor O1 is equal to 12. Therefore, the voltage on the emitter of transistor Q2 is equal to l2 (R1 R2), which equals (R1 +R2)VBEQl/R2.

Resistor R3 provides the base current to transistors Q2 and Q3, and further provides collector current for transistor 01. The transistors Q2 and Q3 are therefore conducting, and thereference voltage output on terminal 22 is equal to the voltage of the emitter of transistor Q2 plus the base to emitter drop of transistor 02 minus the base to emitter voltage drop of transistor 03. Thus VREF equals (R1 R2) .VBEQl/RZ I VBEQ2 VBEQ3. It may be seen that though the base to emitter voltage sensitivity of transistor Q2 may be substantially cancelled by the equivalent sensitivity of transistor O3 in the above equation, the reference voltage is substantially directly proportional to the base to emitter diode voltage of transistor Q1, and therefore, except for the effects of transistors Q4 and Q5, will exhibit substantially the entire temperature sensitivity of that base to emitter voltage drop.

Now considering the effects of transistors 04 and Q5, it may be seen that Q5 has its base connected to its collector and is connected through resistor R5 to the emitter of transistor 03. The emitter of O5 is connected to ground. Thus 05 functionsas a diode with a diode forward conduction voltage drop equal to the base to emitter voltage drop of the transistor. The base of transistor O4 is also connected to the base of transistor Q5 buthasaresis tor R4 coupling its emitter to the ground terminal. Resistor R4 is a relatively low valued resistor and is specifically chosen so as to limit the collector and emitter currents of transistors Q4. Thus, it may be seen that the base to emitter voltage of transistor O5 is equal to the base to emitter voltage of transistor Q4 plus the voltage drop across resistor R4, or stated differently, the voltage across resistor R4 is equal to the base to emitter voltage of transistor 05 minus the base to emitter voltage of transistor 04. Consequently I4 ==(VBEQS VBEQ4)/R4.

The current l4 flow through transistor Q2 and resistor R1, and consequently the emitter voltage of transistor Q2 is increased as a result of the circuitry comprising transistor Q4 and Q5 by an amount approximately equal to I4 times R1. This, in turn, increases the emitter voltage of transistor Q3 by a similar amount (neglecting for the time being the change in VBEQ2 as a result of the increased current through transistor Q2). Thus the final equation for the reference voltage at terminal 22 is given by the following approximate equation:

It is to be noted that the value of the forward biased temperature coefficient of a junction diode such as a silicon or germanium diode is current dependent. (integrated circuits are comprised .of silicon transistors and thus the base to emitter voltage of such transistors exhibits the characteristic silicon diode temperature coefficient.) As the diode forward conduction current becomes larger, the absolute value of this coefficient becomes smaller. (The sign of the coefficient of VBE is actuallynegative.) Therefore, since the emitter current in O4 is smaller than that of Q5, the voltage on resistor R4 increases rapidly with increasing temperature. Therefore, the current I4 has a positive temperature coefficient, with a value depending on the values of resistors R4 and R5. In terms of the previous equation for the reference voltage, the selection of resistors R4 and R5 will determine the difference between VBEQ4 and VBEQS. Similarly, the selection of R4 in proportion to R1 and R2 determines the multiplying factor for this difference in emitter to base voltage temperature coefficient so as to provide a temperature sensitivity of opposite polarity as to the otherwise predominate temperature sensitivity due to VBEQl. It should be noted also that while the primary term determining the reference voltage is dependent on VB EQl, the term allowing for correction of the temperature sensitivity is proportional tothe difference intwo base emitter voltages, and though the temperature sensitivity of the base to emitter voltages is highly current dependent, the absolute value of the base to emitter voltage is characteristically only slightly current dependent. That is to say, VBEQ4 VBEQS is, in general, a very small number in comparison to VBEQl, though it does exhibit the highly desired temperature sensitivity. Consequently, the inclusion of the circuitry comprising transistor Q4 and transistor Q5 and resistors R4 and R5 will only require a moderate change to resistors R1 and/or R2 to achieve the desired reference voltage, but the proper cuits, are well within the spirit and scope of the invention.

I claim: p

l. A reference generator circuit having a power input terminal, a reference voltage output terminal and a common input-output terminal comprising; a diode means, first and second transistors of a first conductivity type, first, second and third resistors, first, second and third current supplying means and an output means, said first transistor having its emitter coupled to said common input-output terminal, its collector coupled to said power input terminal through said first cur rent supplying means, and its base coupled to its emitter through said first resistor, said second current supplying means being coupled to said base of said first transistor through said second resistor and being respon sive to the collector voltage on said first transistor, said diode means being coupled between said third current supplying means and said common input-output terminal, said second transistor having its emitter coupled to said common input-output terminal through said third resistor, its base coupled to said diode means, and its collector coupled to at least one of said first and second resistors, said output meansbeing coupled between said second current supplying means and said output terminal and being a means for providing an proportioning resistors R4 and R5 in relation to each other and further in relation to resistor R1 will allow the reduction, substantial cancellation or even reversal of the temperature sensitivity of the reference voltage, as desired. In particular, while the reference voltage would normally havea temperature sensitivity of approximately the temperature sensitivity of the base to emitter diode drop multiplied by the value of (R1 R2)/R2, this temperature sensitivity may be reduced to approximately that of only a single base to emitter diode drop so as to compensate for the base to emitter voltage drop in the current sources of FIG. 1, or to provide such other controlled and predetermined tempera ture sensitivity for the reference voltage as required to enhance the operation of the circuitry connected to such reference voltage generator or a broader temperature range. It should'be noted further that there is no primary power supply voltage dependence on the reference voltage generated by the circuit of the present invention. Thus, the reference voltage is substantially power supply voltage independent, varying slightly as a result of variation primarily in the base to emitter voltages of the various transistors as a result of a change in current there-through caused by the change in power supply voltage.

Having now described the present invention and reference generator and the operation thereof in detail with respect to a particular preferred circuit, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. By way of example, the present invention is ideally suited for fabrication in integrated circuit form, through fabrication with discrete components and/or semiconductor devices other than silicon devices or of devices of the opposite conductivity type (e.g., PNP devices), as well as fabrication with different coupling ciroutput voltage responsive to the voltage on said second resistor.

2. The reference generator circuit of claim 1 wherein said diode means is a third transistor of saidfirst conductivity type, said third transistor having its emitter coupled to said common input-output terminal, its 001- lector coupled to said third current supplying means and its base coupled to its collector.

3. The reference generator circuit of claim 2 wherein said third current supplying means comprises a fourth resistor coupled between said reference voltage output terminal and said collector of said third transistor.

4. The reference generator circuit of claim 3 wherein said first current supplying means comprises a resistor coupled between said power input terminal and the collector of said first transistor. g

5. The reference generator'of claim 4 wherein said second current supplying means comprises a fourth transistor of said first conductivity type, said fourth transistor having its emitter coupled to said second resistor, its collector coupled to said power input terminal and its base coupled to the collector of said-first transistor.

6. The reference generator circuit of claim 5 wherein said output means comprises a fifth transistor of said first conductivity type having its base coupled to the base of said fourth transistor, its collector coupled to said power input terminal and said emitter coupled to said reference voltage output terminal.

7. The reference generator circuit of claim 6 wherein all of said transistors of said first conductivity type are NPN transistors and said power input terminal is the positive terminal.

8. A reference generator circuit having a power input terminal, a common input-output terminal and a reference voltage output terminal comprising first, second, third, fourth and fifth transistors of a first conductivity type, each having an emitter, a base and a collector, and first, second, third, fourth and fifth resistors, said first transistor having its said emitter coupled to said common input-output terminal, its said collector coupled to said power input terminal through said'first resistor, and its said base coupled to its said emitter through said second resistor, said second transistor having its said collector coupled to said power input terminal, its said base coupled to said collector of said first transistor, and its said emitter coupled to said base of said first transistor through said third resistor, said third transistor having its said collector coupled to said power input terminal, its said base coupled to said base of said second transistor, and its said emitter coupled to said reference voltage output terminal, said base of said fourth and fifth transistors being coupled to said collector of said fourth transistor and to said reference voltage output terminal through said fourth resistor, said emitter of said fourth transistor being coupled to said common input-output terminal, said emitter of said fifth transistor being coupled to said common input-output terminal through said fifth resistor, and said collector of said fifth transistor being coupled to at least one of said second and third transistors.

9. The reference generator circuit of claim 8 wherein all of said transistors of said first conductivity type are NPN transistors and said power input terminal is the positive terminal.

10. A compensated reference voltage circuit comprising:

a reference voltage circuit means having at least a first transistor with an emitter, a base and a collector, said reference voltage circuit means also having means coupled to said emitter, said base and said collector for biasing said first transistor into conduction, said reference voltage circuit means being a means for presenting a reference voltage responsive to the base emitter voltage of said first transistor;

a compensating circuit means coupled to said reference voltage circuit means and having at least sec- 0nd and third transistors each having an emitter, a base and a collector, said compensating circuit means including means for biasing said second and third transistors into different levels of conduction, said compensating circuit means being a means for providing a compensation signal responsive to the difference in the base to emitter voltages of said second and third transistors, said reference voltage circuit means further being responsive to said compensation signal to provide a reference voltage having a predetermined temperature variation.

11. The compensation reference voltage circuit of claim 10 wherein said compensating circuit further includes a first resistor, said base of said second transistor being coupled to said base and said collector of said third transistor, and said emitter of said second transistor being coupled through said first resistor to said emitter of said third transistor, the current'in said collector of said second transistor providing said compensation signal.

Claims

1. A reference generator circuit having a power input terminal, a reference voltage output terminal and a common input-output terminal comprising; a diode means, first and second transistors of a first conductivity type, first, second and third resistors, first, second and third current supplying means and an output means, said first transistor having its emitter coupled to said common input-output terminal, its collector coupled to said poWer input terminal through said first current supplying means, and its base coupled to its emitter through said first resistor, said second current supplying means being coupled to said base of said first transistor through said second resistor and being responsive to the collector voltage on said first transistor, said diode means being coupled between said third current supplying means and said common input-output terminal, said second transistor having its emitter coupled to said common input-output terminal through said third resistor, its base coupled to said diode means, and its collector coupled to at least one of said first and second resistors, said output means being coupled between said second current supplying means and said output terminal and being a means for providing an output voltage responsive to the voltage on said second resistor.

2. The reference generator circuit of claim 1 wherein said diode means is a third transistor of said first conductivity type, said third transistor having its emitter coupled to said common input-output terminal, its collector coupled to said third current supplying means and its base coupled to its collector.

4. The reference generator circuit of claim 3 wherein said first current supplying means comprises a resistor coupled between said power input terminal and the collector of said first transistor.

5. The reference generator of claim 4 wherein said second current supplying means comprises a fourth transistor of said first conductivity type, said fourth transistor having its emitter coupled to said second resistor, its collector coupled to said power input terminal and its base coupled to the collector of said first transistor.

8. A reference generator circuit having a power input terminal, a common input-output terminal and a reference voltage output terminal comprising first, second, third, fourth and fifth transistors of a first conductivity type, each having an emitter, a base and a collector, and first, second, third, fourth and fifth resistors, said first transistor having its said emitter coupled to said common input-output terminal, its said collector coupled to said power input terminal through said first resistor, and its said base coupled to its said emitter through said second resistor, said second transistor having its said collector coupled to said power input terminal, its said base coupled to said collector of said first transistor, and its said emitter coupled to said base of said first transistor through said third resistor, said third transistor having its said collector coupled to said power input terminal, its said base coupled to said base of said second transistor, and its said emitter coupled to said reference voltage output terminal, said base of said fourth and fifth transistors being coupled to said collector of said fourth transistor and to said reference voltage output terminal through said fourth resistor, said emitter of said fourth transistor being coupled to said common input-output terminal, said emitter of said fifth transistor being coupled to said common input-output terminal through said fifth resistor, and said collector of said fifth transistor being coupled to at least one of said second and third transistors.

10. A compensated reference voltage circuit comprising: a reference voltage circuit means having at least a first transistor with an emitter, a base and a collector, said reference voltage circuit means also having means coupled to said emitter, said base and said collector for biasing said first transistor into conduction, said reference voltage circuit means being a means for presenting a reference voltage responsive to the base emitter voltage of said first transistor; a compensating circuit means coupled to said reference voltage circuit means and having at least second and third transistors each having an emitter, a base and a collector, said compensating circuit means including means for biasing said second and third transistors into different levels of conduction, said compensating circuit means being a means for providing a compensation signal responsive to the difference in the base to emitter voltages of said second and third transistors, said reference voltage circuit means further being responsive to said compensation signal to provide a reference voltage having a predetermined temperature variation.

11. The compensation reference voltage circuit of claim 10 wherein said compensating circuit further includes a first resistor, said base of said second transistor being coupled to said base and said collector of said third transistor, and said emitter of said second transistor being coupled through said first resistor to said emitter of said third transistor, the current in said collector of said second transistor providing said compensation signal.