Systems and methods for high-sensitivity detection of input bias current

• US 8,130,032 B1
• Filed: 09/29/2010
• Issued: 03/06/2012
• Est. Priority Date: 09/29/2010
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Heaton, Dale Alan, Guidry, David Walker
• Primary Examiner(s): Nguyen, Hieu
• Application Number:
  US12/893,346
• Publication Number:
  US 20120075014A1
• Time in Patent Office: 524 Days
• Field of Search: 330252-261, 330/2, 330/69
• US Class Current: 330/2
• CPC Class Codes: G01R 19/0023 Measuring currents or voltages from sources with high internal resistance by means of measuring circuits with high input impedance, e.g. OP-amplifiers electrostatic instruments G01R5/28; measuring electrostatic potential G01R15/165; measuring electrostatic fields G01R29/12; amplifiers per se H03F
• CPC Class Codes: G11C 29/021 in voltage or current generators
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters

Abstract

The invention relates to systems and methods for high-sensitivity detection of input bias current. The invention more particularly relates to platforms and techniques for the calibration and measurement of input bias current in op amps or other devices. In embodiments, the platform can incorporate a servo loop connected to a high-sensitivity test amplifier, such as an instrumentation amplifier. The test amplifier can complete a switchable circuit with the servo loop and detect a calibration input bias current for the test platform, without a production device in place. The device under test can be switched into the servo loop, and the total bias current measured with both the device under test and test amplifier in-circuit. The difference between the measured current with the device inserted and the previously measured calibration current represents the bias current for the subject device, without attaching external meters or requiring reference parts of the production type.

Claims

1. An apparatus for measuring an input bias current in an operational amplifier, comprising:

a servo loop;

a low-leakage amplifier connected to the servo loop;

a receptacle for the operational amplifier, the receptacle being configured to couple the operational amplifier to the low-leakage amplifier and to the servo loop when the operational amplifier is mounted in the receptacle;

wherein the servo loop is configured to generate—

a first leakage current of the low-leakage amplifier without the operational amplifier mounted in the receptacle, and

a second leakage current of the low-leakage amplifier coupled to the operational amplifier with the operational amplifier mounted in the receptacle, and

wherein the input bias current of the operational amplifier is generated by subtracting the first leakage current from the second leakage current.

2. The apparatus of claim 1, wherein the low-leakage amplifier comprises an instrumentation amplifier.

3. The apparatus of claim 2, wherein the instrumentation amplifier comprises an instrumentation operational amplifier coupled to a high-impedance input buffer.

4. The apparatus of claim 1, wherein the low-leakage amplifier is connected to a switch to connect the low-leakage amplifier to the servo loop.

5. The apparatus of claim 4, wherein the switch comprises a relay.

6. The apparatus of claim 1, wherein the low-leakage amplifier is connected to at least one switch to connect the low-leakage amplifier to at least one capacitor to integrate a voltage present on at least one input pin of the low-leakage amplifier.

7. The apparatus of claim 6, wherein the at least one switch comprises a relay.

8. The apparatus of claim 1, wherein the operational amplifier is connected to at least one switch to connect the operational amplifier to at least one capacitor to integrate a voltage present on at least one input pin of the operational amplifier.

9. The apparatus of claim 8, wherein the at least one switch comprises a relay.

10. The apparatus of claim 8, further comprising at least one guard circuit configured to shunt a voltage potential between the at least one input pin of the operational amplifier and the at least one guard circuit to ground.

11. The apparatus of claim 1, wherein the receptacle comprises a chip socket.

12. The apparatus of claim 1, wherein the low-leakage amplifier and the operational amplifier are connected in parallel.

13. The apparatus of claim 1, wherein the low-leakage amplifier and the operational amplifier each comprise a non-inverting input pin and an inverting input pin.

14. The apparatus of claim 1, wherein the low-leakage amplifier and the operational amplifier are coupled within a distance of substantially 5 millimeters.

15. A method of measuring an input bias current in an operational amplifier, comprising:

measuring a first leakage current produced by a low-leakage amplifier connected to a servo loop;

coupling the low-leakage amplifier to the operational amplifier;

connecting the coupled low-leakage amplifier and operational amplifier to the servo loop;

measuring a second leakage current produced by the coupled low-leakage amplifier and operational the low-leakage amplifier via the servo loop; and

subtracting the first leakage current from the second leakage current to generate the input bias current of the operational amplifier.

16. The method of claim 15, wherein the low-leakage amplifier comprises an instrumentation amplifier.

17. The method of claim 16, wherein the instrumentation amplifier comprises an instrumentation operational amplifier coupled to a high-impedance input buffer.

18. The method of claim 15, wherein the low-leakage amplifier is connected to a switch to connect the low-leakage amplifier to the servo loop.

19. The method of claim 18, wherein the switch comprises a relay.

20. The method of claim 15, wherein the low-leakage amplifier is connected to at least one switch to connect the low-leakage amplifier to at least one capacitor to integrate a voltage present on at least one input pin of the low-leakage amplifier.

21. The method of claim 20, wherein the at least one switch comprises a relay.

22. The method of claim 20, further comprising activating at least one guard circuit configured to shunt a voltage potential between the at least one input pin of the operational amplifier and the at least one guard circuit to ground.

23. The method of claim 15, wherein the operational amplifier is connected to at least one switch to connect the operational amplifier to at least one capacitor to integrate a voltage present on at least one input pin of the operational amplifier.

24. The method of claim 23, wherein the at least one switch comprises a relay.

25. The method of claim 15, wherein the receptacle comprises a chip socket.

26. The method of claim 15, wherein the low-leakage amplifier and the operational amplifier are connected in parallel.

27. The method of claim 15, wherein the low-leakage amplifier and the operational amplifier each comprise a non-inverting input pin and an inverting input pin.

28. The method of claim 15, wherein the low-leakage amplifier and the operational amplifier are coupled within a distance of substantially 5 millimeters.