Highly symmetrical bi-direction current sources

• US 5,760,640 A
• Filed: 12/03/1996
• Issued: 06/02/1998
• Est. Priority Date: 12/06/1995
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Mone, Patrick, Girard, Phillipe
• Primary Examiner(s): Tran, Toan
• Assistant Examiner(s): ZWEIZIG, JEFFERY SHAWN
• Application Number:
  US08/758,334
• Time in Patent Office: 546 Days
• Field of Search: 323/312, 323/315, 323/316, 327/530, 327/538, 327/542, 327/543
• US Class Current: 327/543
• CPC Class Codes: G05F 3/262 using field-effect transistors only
• CPC Class Codes: H03L 7/0896 the current generators being controlled by differential up-down pulses

Abstract

A bi-directional current source which maintains accurate, substantially equal source and sink currents over a large range of output voltages. The current source includes a primary field effect transistor (FET) and two mirroring FET'"'"'s. It additionally includes at least one operational amplifier for voltage balancing. An optional operational amplifier provides and additional bias voltage and transistor matching optionally provides impedance matching of the supply voltages.

Claims

1. A bi-directional current source biased between a first supply voltage and a second supply voltage comprising:

a current generator connected between the first supply voltage and the second supply voltage, the current generator including a first branch having a primary field effect transistor (FET) and a current supply for generating a reference current, the current generator also including a second branch having first and second mirroring FET'"'"'s and first and second complimentary FET'"'"'s and a third branch having first and second output FET'"'"'s;

a switching circuit for selecting either source or sink current to be output by the bi-directional current source; and

a first operational amplifier having inputs connected to the first and second complimentary FET'"'"'s and the switching circuit and an output connected to the second mirroring FET and the second output FET.

2. The bi-directional current source of claim 1 further comprising:

a first p-channel FET disposed between the primary FET and the current supply;

a second p-channel FET disposed between the first mirroring FET and the first complementary FET; and

a second operational amplifier having inputs connected to the primary FET and first mirroring FET and an output connected to the first and second p-channel FET'"'"'s.

3. The bi-directional current source of claim 1 wherein the FET'"'"'s in each branch are substantially identical so that an impedance match is obtained between the first and second supply voltages.

4. The bi-directional current source of claim 2 wherein the FET'"'"'s in each branch are substantially identical so that an impedance match is obtained between the first and second supply voltages.