Calibration of focus error signal offset in a focus servo system
View Patent ↗A focus error signal offset calibration is presented. The focus error signal offset can be calibrated by varying the focus error signal offset to optimize an operating characteristic of the optical disk drive. In some embodiments, the operating characteristic can be a servo function. In some embodiments, the operating characteristics can be a read function.
1. A method of calibrating a focus error signal offset in a focus servo system having a servo processor for an optical disk drive, the method comprising:
closing the focus servo system with the focus error signal offset set to a first value while a tracking servo system is off, the servo processor calculating a focus error signal from optical signals received from detectors in an optical pick-up units;
(a) decrementing the focus error signal offset from a starting value until a maximum in a peak-to-peak value of a tracking error signal is located;
assigning a value of the focus error signal offset corresponding to the maximum of the peak-to-peak value of the tracking error signal determined in act (a) to a current best offset value;
(b) incrementing the focus error signal offset from the starting value until a maximum in the peak-to-peak value of the tracking error signal is located;
if the peak-to-peak value of the tracking error signal determined in act (b) is greater than the peak-to-peak value determined in act (a), assigning the current best offset value to a value of the focus error signal offset corresponding to the maximum of the peak-to-peak value of the tracking error signal determined in act (b).
2. The method of claim 1 , further comprising,
setting the focus error signal offset to the current best offset value.
3. The method of claim 2 , further including calibrating a focus loop gain to set an open loop gain of the focus servo system to a preset value after setting the focus error signal offset.
4. The method of claim 2 , wherein optimizing the performance characteristic of the optical disk drive further includes:
closing the focus servo system;
closing a tracking servo system over a readable portion of an optical medium; and
adjusting the focus error signal offset while monitoring a data jitter until the data jitter is minimized.
5. The method of claim 4 , wherein monitoring the data jitter includes measuring a data error rate during a read operation.
6. The method of claim 1 , wherein the starting value is zero.
7. The method of claim 1 , wherein the starting value is a current value of the focus error signal offset.
8. An optical disk drive, comprising:
an optical pick-up unit;
an analog-to-digital converter coupled to receive signals from detectors in the optical pick-up unit and to digitize the received detector signals;
at least one servo processor coupled to receive the digitized detector signals and to calculate control signals, and
a driver coupled to control positions of the optical pick-up unit in response to the control signals,
wherein the at least one servo processor is configured to execute an algorithm that includes the acts of:
closing a focus servo system with a focus error signal offset set to a first value while a tracking servo system is off, the at least one servo processor calculating a focus error signal from the digitized detector signals;
(a) decrementing the focus error signal offset from a starting value until a maximum in a peak-to-peak value of a tracking error signal is located;
assigning a value of the focus error signal offset corresponding to the maximum of the peak-to-peak value of the tracking error signal determined in act (a) to a current best offset value;
(b) incrementing the focus error signal offset from the starting value until a maximum in the peak-to-peak value of the tracking error signal is located;
if the peak-to-peak value of the tracking error signal determined in act (b) is greater than the peak-to-peak value determined in act (a), assigning the current best offset value to a value of the focus error signal offset corresponding to the maximum of the peak-to-peak value of the tracking error signal determined in act (b).
9. The drive of claim 8 , wherein the algorithm further includes instructions that calibrate a focus loop gain.