Granted Patent B2

US 6,904,007 · App. 09/950,519 · Granted Jun 7, 2005

Abstract

Claims (16)

1. A method of calibrating a loop gain of a loop gain amplifier in a digital servo system, comprising: receiving optical signals from an optical pick-up unit in an optical disk drive; closing the digital servo system with a first loop gain, the digital servo system calculating a control signal based on the optical signals; applying a sinusoidal disturbance at a cross-over frequency to the control signal generated by the digital servo system to form a second control signal; controlling a position of the optical pick-up unit with the second control signal; calculating a discrete Fourier transform of the sinusoidal disturbance at the cross-over frequency to form a disturbance DFT; calculating a discrete Fourier transform of the control signal to form a signal DFT; calculating a measured loop gain from a ratio of the disturbance DFT and the signal DFT; and calculating the loop gain from a ratio between the first loop gain and the measured loop gain.

2. The method of claim 1 , wherein the digital servo system is a tracking servo system.

3. The method of claim 2 , wherein closing the digital servo system with a first loop gain includes closing a focus servo system with a focus loop gain; and closing the tracking servo system with the first loop gain.

4. The method of claim 2 , wherein the cross-over frequency is about 1.8 kHz.

5. The method of claim 1 , wherein the digital servo system is a focus servo system.

6. The method of claim 5 , wherein the cross-over frequency is about 1.5 kHz.

7. The method of claim 1 , wherein calculating the loop gain includes dividing the first gain by the measured loop gain and multiplying by a desired loop gain at the second control signal.

8. The method of claim 1 , wherein the desired loop gain is unity.

9. An optical disk drive, comprising: an optical pick-up unit; an analog processor coupled to receive signals from detectors in the optical pick-up unit and provide digital signals; at least one processor coupled to receive the digital signals, the at least one processor calculating at least one control signal; and a driver coupled to control a position of the optical pick-up unit in response to the at least one control signal, wherein the at least one processor executes an algorithm that closes a digital servo system with a loop gain amplifier with a first loop gain, the digital servo system calculating a control signal based on the digital signals, applies a sinusoidal disturbance at a cross-over frequency to the control signal generated by the digital servo system to form a second control signal, substitutes the second control signal for the control signal, calculates a discrete Fourier transform of the sinusoidal disturbance at the cross-over frequency to form a disturbance DFT, calculates a discrete Fourier transform of the control signal to form a signal DFT, calculates a measured loop gain from a ratio of the disturbance DFT and the signal DFT, and calculates a loop gain from a ratio between the first loop gain and the measured loop gain.

10. The drive of claim 9 , wherein the digital servo system is a tracking servo system.

11. The drive of claim 10 , wherein closing the digital servo system with a first loop gain includes closing a focus servo system with a focus loop gain; and closing the tracking servo system with the first loop gain.

12. The drive of claim 10 , wherein the cross-over frequency is about 1.8 kHz.

13. The drive of claim 9 , wherein the digital servo system is a focus servo system.

14. The drive of claim 13 , wherein the cross-over frequency is about 1.5 kHz.

15. The drive of claim 9 , wherein the loop gain is calculated by dividing the first gain by the measured loop gain and multiplying by a desired loop gain at the second control signal.

16. The drive of claim 15 , wherein the desired loop gain is unity.

Assignments (12)