United States Patent: 3601687

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United States Patent	3,601,687
Tu	August 24, 1971

LOW-IMPEDANCE VOLTAGE SUPPLY

Abstract

A low-impedance voltage supply for providing a relatively constant reference voltage independent of the magnitude of the current flowing through the source. The circuit includes a transistor whose base is connected to the junction of two resistors in a voltage divider network. The voltage divider network is driven from a diode connected through a resistor to a potential source. The collector of the transistor is connected to another diode which is fed through the same resistor from the potential source.

Inventors:	Tu; George K. (N/A, NY)
Assignee:	Corporation; Cogar (Wappingers Falls, NY)
Appl. No.:	05/048,204
Filed:	June 22, 1970

Current U.S. Class: 323/313

Current International Class: G05F 3/08 (20060101); G05F 3/22 (20060101); G05F 001/56 ()

Field of Search: 307/296,297 323/1,4,16,17,19,22T,39,8

References Cited [Referenced By]

U.S. Patent Documents


3223781	December 1965	Hestad
3246233	April 1966	Herz
3413537	November 1968	Sharp et al.
3509451	April 1970	Garrett

Other References

3D. C. Chang, "Reference Voltage Circuit," IBM Technical Disclosure Bulletin, Vol. 12, No. 6, Nov. 1969, pgs. 841, 842 (copy in 323-16).

Primary Examiner: Miller; J. D.
Assistant Examiner: Pellinen; A. D.

Claims

What I claim is:

1. A low-impedance voltage supply comprising a transistor having emitter, base and collector terminals, a source of ground potential, means connecting said emitter terminal to said source of ground potential, first impedance means connected between said base terminal and said source of ground potential, a pair of diodes, power supply means, second impedance means connected between said power supply means and the anode of each of said diodes, third impedance means connected between the cathode of one of said diodes and said base terminal, and means connecting the cathode of the other of said diodes to said collector terminal.

2. A low-impedance voltage supply in accordance with claim 1 wherein said power supply means serves to power an external load circuit connected therebetween and the collector terminal of said transistor.

3. A low-impedance voltage supply in accordance with claim 1 wherein said first, second and third impedance means have magnitudes such that the collector potential of said transistor is high enough to prevent the saturated operation thereof.

4. A low-impedance voltage supply comprising a transistor having emitter, base and collector terminals, a first source of potential, means connecting said emitter terminal to said first source of potential, first impedance means connected between said base terminal and said first source of potential, a pair of diode means, a second source of potential, second impedance means connected between said second source of potential and one end of each of said diode means, third impedance means connected between the other end of one of said diode means and said base terminal, and means connecting the other end of the other one of said diode means to said collector terminal, said collector terminal being the output terminal of the voltage supply.

5. A low-impedance voltage supply in accordance with claim 4 wherein said second source of potential is operative to power an external load circuit connected therebetween and the collector terminal of said transistor.

6. A low-impedance voltage supply in accordance with claim 5 wherein said first, second and third impedance means have magnitudes such that the collector potential of said transistor is high enough to prevent the saturated operation thereof.

7. A low-impedance voltage supply in accordance with claim 4 wherein said first, second and third impedance means have magnitudes such that the collector potential of said transistor relative to the potential of said first source is such that said transistor is nonsaturated.

8. A low-impedance voltage supply comprising a transistor having emitter, base and collector terminals, a first source of potential, means connecting said emitter terminal to said first source of potential, first impedance means connected between said base terminal and said first source of potential, a second source of potential, second impedance means connected at one end to said second source of potential, means for supplying a variable load current to said collector terminal, and feedback means connected between said collector terminal, the other end of said second impedance means and said base terminal for controlling increased conduction in said transistor responsive to an increase in current from said variable load current means.

9. A low-impedance voltage supply in accordance with claim 8 wherein said feedback means is operative to control the potential of the collector of said transistor relative to the potential of said first source such that said transistor is nonsaturated.

Description

This invention relates to voltage supplies and, more particularly, to a low-impedance voltage supply.

In many integrated circuit systems it is necessary to provide a low-impedance voltage supply. Such a supply provides a relatively constant reference potential independent of the magnitude of the current which is caused to flow through it by an external circuit to which the reference potential is extended. A typical application for such a voltage supply is a memory system of the type disclosed in the copending application of Tu and Bryant, Ser. No. 17,567, filed March 9, 1970. In such a system, it is necessary to maintain the potential of a drive/sense line relatively constant independent of the current which flows through the line. No current normally flows through the line, but current does flow when a memory cell is interrogated. For the proper operation of the cell, it is necessary for the reference voltage to remain relatively constant even as the current in the line increases. In the prior art, low-impedance voltage supplies have been provided only with the use of large numbers of active devices.

It is a general object of my invention to provide a low-impedance voltage supply which requires the use of a minimal number of active devices.

Briefly, in accordance with the principles of my invention, in the illustrative embodiment of the invention the voltage supply comprises a single transistor, the emitter of which is connected to ground. A pair of series-connected resistors is provided, with one end of the series connection being connected to ground and the other being extended through a diode and a resistor to a voltage source. The junction of the two resistors is connected to the base of the transistor. The collector of the transistor is extended through another diode to the same resistor and power supply. This configuration provides a very low impedance at the collector terminal of the transistor; that is, the collector potential does not vary substantially as current delivered from an external source to the collector terminal varies by as much as 10 milliamperes.

It is a feature of my invention to provide a low-impedance voltage supply which consists of a single transistor, the base of which is driven from a voltage divider network, and a pair of diodes for connecting a source of potential through a resistor respectively to the voltage divider network and the collector terminal of the transistor.

Further objects, features and advantages of my invention will become apparent upon a consideration of the following detailed description in conjunction with the drawing which depicts an illustrative embodiment of the invention.

The voltage supply includes a transistor Q2 whose emitter is grounded. The base of the transistor is connected to the junction of resistors R2 and R3. Double-emitter transistor Q1 has its collector and base terminals shorted together and thus serves in the capacity of a pair of diodes. The collector of transistor Q2 is connected to one of the emitters and resistor R2 is connected to the other emitter. The collector of transistor Q1 (the anode of the two diodes) is connected through resistor R1 to potential source B which has a magnitude of 5 volts. The collector terminal VR of the transistor serves as the output terminal of the voltage supply. A load current source, ICS, which is shown as being variable, is connected between supply B and the output terminal VR. As will be shown, the potential at terminal VR does not change substantially as the magnitude of the current from source ICS varies all the way from 0 to 10 milliamperes.

With transistor Q2 conducting, the base-emitter drop of the transistor is 0.8 volts. With negligible current flowing to the base of the transistor, all of the current through resistor R3 flows through resistor R2 as well. In the illustrative embodiment of the invention, resistor R3 has a magnitude of 400 ohms and resistor R2 has a magnitude of 200 ohms. Consequently, the drop across resistor R2 is half of the drop across resistor R3. Since the drop across resistor R3 is 0.8 volts, the drop across resistor R2 is 0.4 volts, and the leftmost emitter of transistor Q1 is held at a potential of 1.2 volts.

Current flows from source B through resistor R1, the leftmost emitter of transistor Q1 and resistors R2 and R3. With a 0.8 volt drop across the leftmost diode (transistor Q1 can be thought of as comprising two diodes), and with the leftmost emitter being held at a potential of 1.2 volts, the collector of transistor Q1 is at a potential of 2 volts. Consequently, since potential source B has a magnitude of 5 volts, 3 volts appear across resistor R1. Since resistor R3 has a magnitude of 400 ohms and there is a drop of 0.8 volts across it, the current through resistor R3 is 2 milliamperes.

Assuming that the load current is initially zero, the only current flowing through the collector of transistor Q2 is derived from the rightmost diode of transistor Q1. Assume that the potential at terminal VR is to be 1.2 volts in the absence of any external current flow. Let it further be assumed that the current flow through transistor Q2 is to be 1 milliampere as a result of current flowing through the rightmost diode. In such a case, the current which flows through resistor R1 is the sum of the 1 milliampere which flows through transistor Q2 and the 2 milliamperes which flow through resistors R2 and R3. Thus, 3 milliamperes flow through resistor R1, across which there is a 3 volt drop. Consequently, the magnitude of resistor R1 is 1,000 ohms. Assuming a current gain of 100 for transistor Q2, with 1 milliampere flowing into the collector of the transistor, only 10 microamperes flow into the base. This justifies the assumption above that the same current (2 milliamperes) flows through resistors R2 and R3; although the current through resistor R3 is less than the current through resistor R2 by 10 microamperes, the difference is negligible.

Consider now the case in which the external load current ICS increases to 10 milliamperes. In such a case, the current flow through the collector of transistor Q2 is 11 milliamperes--the sum of the 10 milliampere load current and the 1 milliampere current through the rightmost diode. With 11 milliamperes now flowing into the collector of transistor Q2, since the current gain of the transistor is 100, the base current is increased to 0.11 milliamperes. Since the base of transistor Q2 is held at 0.8 volts due to the 0.8 volt drop across the base-emitter junction of the transistor, 2 milliamperes still flow through resistor R3. However, 2.11 milliamperes now flow through resistor R2 as a result of the increased base current into transistor Q2. The drop across resistor R2 is thus (200 ohm) (2.11.times.10.sup..sup.-3 amp) or 0.422 volts. Since the junction of resistors R2 and R3 is at 0.8 volts and there is an additional 0.8 volt drop across transistor Q1, the collector of transistor Q1 is at a potential of 1.6+0.422 or 2.022 volts.

The drop across resistor R1 is thus 5-2.022 volts or 2.978 volts. Since resistor R1 has a magnitude of 1,000 ohms, the current flowing through it is 2.978 milliamperes.

Since the drop across the rightmost diode is 0.8 volts and the collector of transistor Q1 is at a potential of 2.022 volts, output terminal VR is at a potential of 2.022-0.8, or 1.222 volts. It is thus seen that the output voltage increases from 1.2 volts with no external load current to 1.222 volts with a 10 milliampere load current. The output voltage variation is only 22 millivolts for a 10 milliampere increase in load current.

It should be noted that resistors R1, R2 and R3 are selected such that the potential at terminal VR in the absence of external load current flow is 1.2 volts--considerably higher than the potential of 0.2 volts which would cause transistor Q2 to saturate.

The diode connection serves a feedback function. An increase in load current ICS causes the current through the rightmost diode to decrease slightly. This, in turn, causes the current through the leftmost diode to increase. This increased current provides a greater base drive for transistor Q2, which greater base drive allows the transistor to conduct the larger load current ICS.

It is also of interest to consider the ratio of "on power" to "standby power." In the standby mode--when no external current flow--current source B delivers 3 milliamperes to the voltage supply. Since the current source has a magnitude of 5 volts, the power dissipated in (3 milliamperes).times.(5 volts), or 15 milliwatts. On the other hand, when the external circuit operates and 10 milliamperes flow into the collector of transistor Q2, assuming that the external circuit is powered by the same power supply as shown in the drawing, the power supply delivers a total of (12.978 milliamperes)-(10 milliamperes) to the external load circuit and 2.978 milliamperes to resistor R1 as derived above. In such a case, the power dissipated is (12.978 milliamperes).times.(5 volts) or 64.890 milliwatts. The ratio of "on power" to "standby power" is thus 64.89/15, in excess of 4. As will be appreciated by those skilled in the art, this is a relatively high and therefore desirable ratio which is obtained at the same time that the reference voltage varies by only 22 millivolts.

Although the invention has been described with reference to a particular embodiment, it is to be understood that this embodiment is merely illustrative of the application of the principles of the invention. Numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention.

* * * * *

Current U.S. Class:	323/313
Current International Class:	G05F 3/08 (20060101); G05F 3/22 (20060101); G05F 001/56 ()
Field of Search:	307/296,297 323/1,4,16,17,19,22T,39,8