Method and system for power amplifier offset nulling

• US 6,262,619 B1
• Filed: 04/27/1999
• Issued: 07/17/2001
• Est. Priority Date: 04/27/1999
• Status: Active Grant

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: McGreer, Brooke, Rowan, Bryan Scott
• Primary Examiner(s): Lam, Tuan T.
• Assistant Examiner(s): Nguyen, Hiep
• Application Number:
  US09/300,652
• Time in Patent Office: 812 Days
• Field of Search: 360/75, 360/78.04, 360/77.04, 360/78.05, 318/634, 327/307, 327/513, 327/362, 327/378
• US Class Current: 327/307
• CPC Class Codes: G11B 5/59627 Aligning for runout, eccentricity or offset compensation G11B5/5534, G11B5/59677, G11B5/59688 take precedence
• CPC Class Codes: H03F 3/3064 with symmetrical driving of the end stage
• CPC Class Codes: H03F 3/45973 by using a feedback circuit

Abstract

Method and system aspects for nulling output offset current in an amplifier are described. In an exemplary method aspect, the method includes determining at least one offset value with a power amplifier in at least one mode. The at least one offset value then utilized to identify an output offset current value in the power amplifier. An adjustment to an input signal to the power amplifier occurs until the output offset current value is substantially nulled to identify a power amplifier offset value.

Claims

1. A method for power amplifier offset nulling, the method comprising the steps of:

a) determining at least one offset value with a power amplifier in at least one mode, including;

a1) determining a first offset value with the power amplifier in a first mode; and

a2) determining a second offset value with the power amplifier in a second mode;

b) utilizing the at least one offset value to identify an output offset current value in the power amplifier; and

c) adjusting an input signal to the power amplifier until the output offset current value is substantially nulled to identify a power amplifier offset value.

2. The method of claim 1, wherein the first mode comprises a brake mode.

3. The method of claim 2, wherein determining a first offset value further comprises measuring offset currents through an analog-to-digital converter and a sensing resistor for storage as the first offset value.

4. The method of claim 1 wherein the second mode comprises a tristate mode.

5. The method of claim 4 wherein determining a second offset value further comprises measuring offset currents through an analog-to-digital converter and a sensing resistor for storage as the second offset value.

6. The method of claim 1 further comprising the step of supplying the power amplifier offset value to the power amplifier with a zero value control output voltage to ensure substantially zero output offset current in the power amplifier.

7. A method for power amplifier offset nulling, the method comprising the steps of:

a) determining at least one offset value with a power amplifier in at least one mode;

b) utilizing the at least one offset value to identify an output offset current value in the power amplifier in a disk drive; and

c) adjusting an input signal to the power amplifier until the output offset current value is substantially nulled to identify a power amplifier offset value.

8. The method of claim 7 further comprising supplying the power amplifier offset when the disk drive is in a parked state.

9. A method for calibrating a power amplifier to achieve power amplifier offset nulling comprising the steps of:

a) determining at least one offset with disabled current flow in a power amplifier, including determining current offsets through an analog-to-digital converter and a sensing resistor when the power amplifier is in first and second modes;

b) applying a control output with a zero voltage value to the power amplifier;

c) utilizing the at least one offset to determine an output offset current in the power amplifier; and

d) determining a necessary adjustment to the control output to substantially null the output offset current.

10. The method of claim 9 further comprising storing the necessary adjustment as a power amplifier offset.

11. The method of claim 10 further comprising applying the power amplifier offset during subsequent applications of a zero control output to ensure substantially zero offset current in the power amplifier.

12. The method of claim 9 wherein the first mode further comprises a brake mode.

13. The method of claim 9 wherein the second mode further comprises a tristate mode.

14. A power amplifier offset nulling system comprising:

a power amplifier;

a load coupled to the power amplifier;

an analog-to-digital (A/D) converter coupled to the power amplifier; and

a controller coupled for providing a control output signal to the power amplifier and for providing an amplifier offset value as an adjustment necessary to ensure power amplifier offset nulling for a zero value control output signal in accordance with calibrated offset values for the load and A/D converter, wherein the calibrated offset values further comprise offset values determined with the power amplifier in a brake mode and in a tristate mode.

15. The system of claim 14 wherein the load further comprises a sensing resistor.

16. The system of claim 15 further comprising a voice coil motor coupled to the sensing resistor.

17. The system of claim 16 wherein the voice coil motor comprises a voice coil motor of a load/unload controller of a disk drive.

18. A computer readable medium containing program instructions for calibrating a power amplifier to achieve power amplifier offset nulling comprising:

determining offsets with disabled current flow in a power amplifier including determining current offsets through an analog-to-digital converter and a sensing resistor when the power amplifier is in first and second modes;

applying a control output with a zero voltage value to the power amplifier;

utilizing the offsets to determine an output offset current in the power amplifier; and

determining a necessary adjustment to the control output to substantially null the output offset current.