Voltage controlled current source for low voltage applications

• US 5,801,524 A
• Filed: 05/27/1997
• Issued: 09/01/1998
• Est. Priority Date: 05/27/1997
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Boerstler, David
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US08/863,151
• Time in Patent Office: 462 Days
• Field of Search: 323/312, 323/315, 323/316, 323/317, 327/530, 327/538, 327/317, 330/252, 330/253, 330/254, 330/257, 330/260
• US Class Current: 323/315
• CPC Class Codes: G05F 3/247 producing a voltage or current as a predetermined function of the supply voltage

Abstract

A differential input, voltage controlled current source utilizing a low supply voltage and realizing a wide common mode input range. The voltage controlled current source provides a differential output current as a function the differential input voltage which is independent of the common mode input voltage level. The voltage controlled current source includes a first and a second differential amplifier receiving the differential input voltage and producing a differential current having a first and second leg. The first leg of the differential output current is tracked by a current mirror which floats as a function of the bias voltage and common mode input voltage. A second floating current mirror tracks the second differential output current leg. The first and second current mirrors are coupled to a replica bias circuit which is connected in parallel with the differential amplifiers. The replica bias and first and second current mirrors are connected across the supply voltage and not cascaded with other circuit functions, making the present invention compatible with low voltage technologies.

Claims

1. A voltage controlled current source utilizing a low supply voltage and a differential input voltage comprising:

a first and a second differential amplifier coupled to a differential input voltage for producing a differential current which is a function of said differential input voltage and independent of a common mode input voltage, said differential current having a first current and a second current;

a first floating current mirror responsive to said first current;

a second floating current mirror responsive to said second current; and

wherein said first and said second floating current mirrors are coupled independently of said first and second differential amplifier to said low supply voltage, allowing utilization of low voltage technology.

2. The voltage controlled current source according to claim 1, wherein an output of said voltage controlled current source remains substantially linear while the common mode input voltage of the differential input voltage ranges from supply voltage high to supply voltage low.

3. The voltage controlled current source according to claim 1, wherein the first differential amplifier is a source coupled N-FET.

4. The voltage controlled current source according to claim 1, wherein the second differential amplifier is a source coupled P-FET.

5. The voltage controlled current source according to claim 1, wherein the first and second floating current mirrors are biased by a replica bias circuit.

6. The voltage controlled current source according to claim 5, wherein said replica bias circuit is a source coupled N-FET pair.

7. The voltage controlled current source according to claim 1, wherein the first and second floating current sources are mirrored by a third and fourth current source.

8. The voltage controlled current source according to claim 1, wherein first and second current mirrors operate responsive to a voltage.

9. The voltage controlled current source according to claim 1, wherein first and second current source drive an output source coupled pair.

10. The voltage controlled current source according to claim 1, wherein output source coupled pair is responsive to a voltage.

11. The voltage controlled current source according to claim 1, wherein output source coupled pair drives a phase mixing apparatus.

12. The voltage controlled current source according to claim 1, wherein output source coupled pair drives a voltage controlled delay line.

13. The voltage controlled current source according to claim 1, wherein output source coupled pair drives an oscillator device.