Tracking and focus servo system with defect detection
View Patent ↗A defect detector in an optical disk drive is presented. The defect detector indicates a defect by monitoring a sum signal. The sum signal is calculated from optical signals from detectors in an optical pick-up unit of the optical disk drive. A defect can be indicated when a filtered sum signal, the filtered sum signal being the sum signal filtered with a high pass filter, is above a threshold value. In some embodiments, the defect detector can recognize changes in laser power or transitions between media types and not indicate defects during those occurrences.
1. A method of detecting a defect in an optical media in an optical disk drive, comprising:
receiving digitized signals from detectors in an optical pick-up unit;
adding the digitized signals to form a sum signal;
filtering the sum signal with a high-pass filter to generate a filtered sum signal;
indicating a defect if the filtered sum signal exceeds a threshold value; and
generating a time-out signal if the defect is detected for a predefined number of cycles.
2. The method of claim 1 , further including
detecting a change in laser power; and
suppressing indication of the defect when the change in laser power is detected.
3. The method of claim 2 , wherein detecting a change in laser power includes receiving notification that the laser power will be changed.
4. The method of claim 3 , wherein receiving notification that the laser power will change includes monitoring a focus sum threshold.
5. The method of claim 3 , wherein suppressing indication of the defect includes delaying detection of defects for a delay time after receiving notification that the laser power will change.
6. The method of claim 1 , further including suppressing indication of the defect when crossing a boundary between media types.
7. The method of claim 6 , wherein suppressing indication of the defect includes
detecting the boundary crossing; and
delaying indication of the defect for a delay time.
8. The method of claim 7 , wherein detecting the boundary crossing includes receiving notification of the boundary crossing.
9. The method of claim 7 , wherein detecting the boundary crossing includes setting the threshold value to a high enough level to ignore boundary crossings.
10. 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 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 calculates a sum signal,
filters the sum signal with a high-pass filter to generate a filtered sum signal, and
indicates a defect if the filtered sum signal exceeds a threshold value.
11. The method of claim 10 , wherein the sum signal is calculated by
receiving the digital signals; and
adding the digital signals to form the sum signal.
12. The method of claim 10 , wherein the algorithm includes further instructions that
generate a time-out signal if the defect is detected for a predefined number of cycles.
13. The method of claim 10 , wherein the algorithm includes further instructions that
detect a change in laser power; and
suppress indication of the defect when the change in laser power is detected.
14. The method of claim 13 , wherein a change in laser power can be detected through receipt of notification that the laser power will be changed.
15. The method of claim 14 , wherein notification that the laser power will change includes monitoring a focus sum threshold.
16. The method of claim 14 , wherein indication of the defect can be suppressed by delaying detection of defects for a delay time after receiving notification that the laser power will change.
17. The method of claim 10 , wherein the algorithm further includes instructions that suppress indication of the defect when crossing a boundary between media types.
18. The method of claim 17 , wherein indication of the defect can be suppressed by
detecting the boundary crossing; and
delaying indication of the defect for a delay time.
19. The method of claim 18 , wherein detecting the boundary crossing includes receiving notification of the boundary crossing.
20. The method of claim 18 , wherein detecting the boundary crossing includes setting the threshold value to a high enough level to ignore boundary crossings.