EP0443238A2 - Präzisionsgeschaltete Stromquelle - Google Patents

Präzisionsgeschaltete Stromquelle Download PDF

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Publication number
EP0443238A2
EP0443238A2 EP90309885A EP90309885A EP0443238A2 EP 0443238 A2 EP0443238 A2 EP 0443238A2 EP 90309885 A EP90309885 A EP 90309885A EP 90309885 A EP90309885 A EP 90309885A EP 0443238 A2 EP0443238 A2 EP 0443238A2
Authority
EP
European Patent Office
Prior art keywords
transistor
current
switch means
source
slave
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP90309885A
Other languages
English (en)
French (fr)
Other versions
EP0443238A3 (en
Inventor
Douglas S. Smith
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Precision Monolithics Inc
Original Assignee
Precision Monolithics Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Precision Monolithics Inc filed Critical Precision Monolithics Inc
Publication of EP0443238A2 publication Critical patent/EP0443238A2/de
Publication of EP0443238A3 publication Critical patent/EP0443238A3/en
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F3/00—Non-retroactive systems for regulating electric variables by using an uncontrolled element, or an uncontrolled combination of elements, such element or such combination having self-regulating properties
    • G05F3/02—Regulating voltage or current
    • G05F3/08—Regulating voltage or current wherein the variable is DC
    • G05F3/10—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics
    • G05F3/16—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices
    • G05F3/20—Regulating voltage or current wherein the variable is DC using uncontrolled devices with non-linear characteristics being semiconductor devices using diode- transistor combinations

Definitions

  • This invention relates to electronic circuitry, and more particularly to a current source capable of being rapidly switched on and off.
  • Switched current sources have been implemented in both bipolar and complementary metal oxide semiconductor (CMOS) formats.
  • CMOS complementary metal oxide semiconductor
  • bipolar current source One of the problems with the bipolar current source is that it is difficult to switch the device cleanly. Rather than immediately producing a constant current output, the emitter voltage of the output transistor exhibits a transient oscillation when switched, which causes the output current to similarly vary from the desired nominal value. This switching transient can be reduced, but to do so requires the addition of more complicated circuitry and a higher voltage source. Also, since current is flowing and the circuit is consuming power regardless of whether it is switched on or off, it is not highly efficient in terms of power consumption.
  • CMOS approach to a switched current source uses a single CMOS transistor which is turned on or off by a voltage control signal applied to its gate.
  • the output current is turned off by applying a large voltage signal to its gate and then switched on with a low voltage signal; the opposite pattern would be used for a depletion device.
  • CMOS transistors are subject to large processing variations; their threshold voltages are difficult to predict, making the ultimate current value obtained from the source similarly difficult to predict.
  • CMOS transistors also have an inherently low output resistance, which is an undesirable characteristic for a current source.
  • the present invention seeks to provide a current source that can be switched on and off under a voltage control, which has a very high compliance when switched on, which consumes little or no power when switched off, exhibits a high output resistance, allows for large swings in the control voltage, and produces an accurate and predictable current output.
  • the invention uses a master-slave circuit in which a first transistor establishes a reference current, and a second transistor is slaved to the first transistor to produce an output current which is proportionate to the reference current.
  • the two transistors are preferably proportionately matched bipolar devices having their bases connected together by an interruptable circuit connection in a current mirror configuration.
  • a current control switch interposed in the base circuit connection connects the transistor bases in one switching state to enable the second transistor to proportionately mirror the first transistor's reference current, and thereby provide a controlled current output. When in the opposite switching state, the switch disconnects the bases of the two transistors, thereby terminating current flow through the second transistor and turning the current source "off".
  • the switch is preferably a field effect transistor (FET), although it may be implemented in other ways such as a diode bridge circuit or a ring of three amplifier.
  • FET field effect transistor
  • a discharge switch preferably in the form of a second FET, is connected to discharge the base of the current source transistor when that transistor is off. For this purpose the discharge transistor is switched in a manner inverse to the current control switch transistor.
  • FIG. 1 is a schematic diagram of one embodiment of the invention.
  • a pair of pnp bipolar transistors Q1 and Q2 have their bases connected together through the source-drain circuit of a metal oxide semiconductor field effect transistor (MOSFET) T1.
  • MOSFET metal oxide semiconductor field effect transistor
  • Q1 and Q2 might also be implemented as CMOS FETs, bipolar transistors are preferable because their current outputs are more predictable; FETs are subject to threshold voltage variations because of processing differences, which make their current levels somewhat unpredictable.
  • the emitters of Q1 and Q2 are connected through current limiting resistors R1 and R2, respectively, to a positive voltage bus 2.
  • the base and collector of Q1 are tied together in a diode configuration so that Q1 draws a constant reference current.
  • the collector of Q1 is connected to ground or to a suitable negative voltage bus.
  • Q2 is proportionately matched with Q1 so that when the MOSFET switch T1 is closed, the base of Q2 is connected to the base of Q1 and Q2 proportionately mirrors the reference current flowing through the collector-emitter circuit of Q1.
  • the Q1/Q2 circuit operates as a conventional current mirror, with Q2 slaved to Q1.
  • the gate of T1 is controlled by a bias voltage V b , which provides the switching control element for the current source.
  • V b When V b is at a voltage level that biases T1 into conduction, the bases of Q1 and Q2 are effectively tied together, causing Q2 to carry an output current I o which proportionately mirrors the known current through Q1, and provides the output current from the current source circuit. Since the current through Q1 can be accurately established and the matching between Q2 and Q1 can also be done accurately when the two transistors are fabricated in the same process, I o can be made very precise.
  • the switching of Q2 by the T1 interconnection is accomplished cleanly, without significant oscillations in the Q2 current output. Q2 carries zero current when T1 is switched off, thus conserving power when the current source is off.
  • T1 can preferably be implemented as any kind of FET, such as a junction FET (JFET).
  • JFET junction FET
  • CMOS complementary metal-oxide-semiconductor
  • CMOS complementary metal-oxide-semiconductor
  • collector-emitter voltage drop typically on the order of 100mV or greater.
  • leakage source current for an FET in an "off" state is on the order of tens or hundreds of microamps, so the FET appears as a low value resistor with a resistance of less than 1 kohm. This results in a very small drain-source voltage drop, typically less than 1mV.
  • FIGs. 2 and 3 Other possible alternatives to the use of an FET for the switch between the bases of Q1 and Q2 are a diode bridge switch and a "ring of three" amplifier, illustrated respectively in FIGs. 2 and 3. These are conventional circuits and need not be described in detail. They are switched by controlling the biasing voltages V b so that their associated switched transistors are turned on and off in tandem. These switched circuits would be connected in the current source circuit of FIG. 1 with their input terminal connected to the base of Q1 and their output terminal to the base of Q2. Although they could provide functional substitutes for a simple FET switch, they are considerably more complex, consume more power, and occupy more space.
  • a second FET T2 has its source-drain circuit connected between the base of Q2 and the positive voltage bus 2.
  • the purpose of T2 is to discharge the base of Q2 when the latter transistor is off. Otherwise, a charge could accumulate at the base of Q2 while it is off, making the circuit more susceptible to noise and radiation, including light.
  • the switching control for T2 is opposite to T1, so that T2 is closed only when T1 is open and Q2 is off. This can conveniently be accomplished with an inverter 4 that inverts V b , the control voltage for T1, and applies the inverted V b to the gate of T2. While T2 is not absolutely required for a functional circuit, it is preferable to have this base discharge function because of the attendant improvement in noise and radiation resistance.
  • FIG. 1 illustrates a circuit with pnp bipolar transistors that provides a controlled current output I o from a positive voltage bus 2.
  • An equivalent circuit can be implemented with npn transistors to provide a controlled current to a negative voltage bus.
  • FIG. 4 Such a circuit is illustrated in FIG. 4, in which elements which are functionally equivalent to those in FIG. 1 are identified by the same reference numerals, and the negative voltage bus is indicated by numeral 6.
  • the described current source has many different applications, and in general can be used whenever a precise switched current source is required.
  • One such application not to be taken as limiting, is a slow oscillator using two of the current sources.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Nonlinear Science (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Automation & Control Theory (AREA)
  • Electronic Switches (AREA)
  • Control Of Electrical Variables (AREA)
  • Dc-Dc Converters (AREA)
EP19900309885 1990-02-20 1990-09-10 Precision switched current source Withdrawn EP0443238A3 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US48231990A 1990-02-20 1990-02-20
US482319 1990-02-20

Publications (2)

Publication Number Publication Date
EP0443238A2 true EP0443238A2 (de) 1991-08-28
EP0443238A3 EP0443238A3 (en) 1992-01-08

Family

ID=23915600

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19900309885 Withdrawn EP0443238A3 (en) 1990-02-20 1990-09-10 Precision switched current source

Country Status (2)

Country Link
EP (1) EP0443238A3 (de)
JP (1) JPH03252217A (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10193507B1 (en) 2017-07-31 2019-01-29 Analog Devices Global Current switching circuit

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3973215A (en) * 1975-08-04 1976-08-03 Rca Corporation Current mirror amplifier
JPS5656036A (en) * 1979-10-12 1981-05-16 Hitachi Ltd Pulse driving circuit
JPH0656935B2 (ja) * 1982-04-24 1994-07-27 日本電装株式会社 定電流制御回路
US4518921A (en) * 1982-10-18 1985-05-21 At&T Bell Laboratories Track and hold circuit
GB2131640B (en) * 1982-12-01 1986-11-19 Plessey Co Plc Switching circuit
US4544878A (en) * 1983-10-04 1985-10-01 At&T Bell Laboratories Switched current mirror
US4814644A (en) * 1985-01-29 1989-03-21 K. Ushiku & Co. Basic circuitry particularly for construction of multivalued logic systems
JPH01128616A (ja) * 1987-11-13 1989-05-22 Fujitsu Ltd 電流スイッチ回路

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10193507B1 (en) 2017-07-31 2019-01-29 Analog Devices Global Current switching circuit

Also Published As

Publication number Publication date
JPH03252217A (ja) 1991-11-11
EP0443238A3 (en) 1992-01-08

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