Digital tracking servo system with multi-track seek with track zero crossing detection

1. A method of detecting zero crossings in a tracking error signal, the method comprising:

delaying for a time period of a half of a cycle of the tracking error signal before detecting when the tracking error signal crosses zero;

detecting when the tracking error signal crosses zero; and,

providing a zero crossing signal that changes state when the tracking error signal crosses zero.

2. The method of claim 1 , wherein detecting when the tracking error signal crosses zero includes detecting when the tracking error signal passes through a range around zero, the range having a positive value above zero and a negative value below zero.

3. A method of multi-track seeking, comprising:

calculating a tracking error signal from digitized optical signals from an optical pick-up unit;

delaying for a time period of a half of a cycle of the tracking error signal before detecting when the tracking error signal crosses zero;

detecting zero crossings in the tracking error signal;

counting the number of zero crossings to form a count;

calculating a reference velocity from the count;

determining a time period between successive zero crossings;

calculating a velocity from the time period;

calculating a velocity error signal between the reference velocity and the velocity;

adjusting a control signal so that the velocity follows the reference velocity; and,

applying the control signal to an actuator coupled to adjust the position of the optical pick-up unit over an optical media.

4. The method of claim 3 , wherein detecting zero crossings in the tracking error signal includes:

detecting when the tracking error signal crosses zero; and,

providing a zero crossing signal that changes state when the tracking error signal crosses zero.

5. The method of claim 4 , wherein detecting when the tracking error signal crosses zero includes detecting when the tracking error signal passes through a range around zero, the range having a positive value above zero and a negative value below zero.

6. A servo system, 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 the digital signals, the processor calculating a control signal; and

a driver coupled to control a position of the optical pick-up unit in response to the control signal;

wherein the at least one processor executes an algorithm that detects zero crossings in a tracking error signal by

delaying for a time period of a half of a cycle of the tracking error signal before detecting when the tracking error signal crosses zero;

detecting when a tracking error signal crosses zero, and

providing a zero crossing signal that changes state when the tracking error signal crosses zero.

7. The method of claim 6 , wherein detecting when the tracking error signal crosses zero includes detecting when the tracking error signal passes through a range around zero, the range having a positive value above zero and a negative value below zero.

8. An optical disk drive, comprising:

means for generating a tracking error signal from digital signals received from an optical pick-up unit;

means for delaying for a time period of a half of a cycle of the tracking error signal before detecting when the tracking error signal crosses zero; and,

means for detecting a zero crossing of the tracking error signal.