Tracking and focus servo system with error signal inverse non-linearity calibration
A digital servo system of an optical disk drive with a calibrated inverse non-linearity function is disclosed. A look-up table is determined, for example, with a focus error signal gain corresponding with a focus error signal offset so that the response of the focus servo system is substantially linear. Additionally, the look-up table can include tracking error signal gain, tracking error signal offset, or tracking loop gain parameters corresponding with the focus error signal offset.
1. A method of providing operating parameters for a digital servo system of an optical disk drive, comprising:
selecting an error signal offset for a digital servo system from a set of error signal offset values;
determining an error signal gain value corresponding to the error signal offset such that a loop gain of the digital servo system is approximately unity; and
storing the error signal gain value in a look-up table.
2. The method of claim 1 , wherein the loop gain is measured at a cross-over frequency.
3. The method of claim 1 , further including
calibrating a second error signal gain in a second digital servo system; and
storing the second error signal gain in the look-up table.
4. The method of claim 3 , further including
calibrating a second error signal offset in the second digital servo system; and
storing the second error signal offset in the look-up table.
5. The method of claim 4 , further including
calibrating a second loop gain in the second digital servo system; and
storing the second loop gain in the look-up table.
6. The method of claim 5 , further including
calibrating a cross-coupling parameter between the digital servo system and the second digital servo system; and
storing the cross-coupling parameter in the look-up table.
7. The method of claim 6 , wherein the digital servo system is a focus servo system and the second digital servo system is a tracking servo system.
8. A method of calibrating inverse non-linearity in a focus servo system and a tracking servo system, comprising:
selecting a focus error signal offset value from a set of offset values;
calibrating a focus error signal gain corresponding to the focus error signal offset; and
storing the focus error signal gain in a look-up table,
wherein, during operation of the focus servo system, the focus servo system looks up the focus error signal gain corresponding to the focus error signal offset in the look-up table.
9. The method of claim 8 , wherein calibrating the focus error signal gain includes adjusting the focus error signal gain until a loop gain of the focus servo system is approximately unity.
10. The method of claim 9 , wherein adjusting the focus error signal gain includes measuring the loop gain of the focus servo system at a cross-over frequency.
11. The method of claim 10 , wherein the cross-over frequency is about 1.5 kHz.
12. The method of claim 8 , further including
calibrating a tracking error signal gain corresponding to the focus error signal offset; and
storing the tracking error signal gain in the look-up table.
13. The method of claim 12 , further including
calibrating a tracking error signal offset corresponding to the focus error signal offset; and
storing the tracking error signal offset in the look-up tables.
14. The method of claim 13 , further including
calibrating a tracking loop gain corresponding to the focus error signal offset; and
storing the tracking loop gain in the look-up table.
15. The method of claim 14 , wherein calibrating the tracking loop gain includes measuring the tracking loop gain at a tracking cross-over frequency.
16. The method of claim 15 , wherein the tracking cross-over frequency is about 1.8 kHz.
17. The method of claim 14 , further including
calibrating a tracking error signal to focus error signal crosstalk parameter; and
storing the crosstalk parameter in the look-up table.
18. 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 control signals; and
a driver coupled to control a position of the optical pick-up unit in response to the control signals,
wherein the at least one processor executes an algorithm that selects a focus error signal offset value from a set of offset values, calibrates a focus error signal gain corresponding to the focus error signal offset,
stores the focus error signal gain in a look-up table, calibrates a tracking error signal gain corresponding to the focus error signal offset;
calibrates a tracking error signal offset corresponding to the focus error signal offset;
calibrates a tracking loop gain corresponding to the focus error signal offset; and
stores the tracking error signal gain, the tracking error signal offset, and the tracking loop gain in the look-up table.