Digital servo system with error signal integrity testing
View Patent ↗A sample integrity test is disclosed. The sample integrity test receives an error signal and a defect signal. If the defect signal indicates the presence of a defect, a low-pass filtered error signal is substituted for the error signal. The low-pass filtered error signal is the error signal filtered with a low-pass filter. The error signal can be derived from optical signals from an optical pick-up unit. A control signal generated from the output signal from the sample integrity test controls the position of the optical pick-up unit. The defect signal can also be derived from the optical signals.
1. A method of performing a signal integrity test in a servo system, comprising: generating an error signal; detecting presence of a defect; and substituting a low pass filtered version of the error signal for the error signal when the defect is detected.
2. The method of claim 1 , wherein detecting presence of the defect includes receiving a defect signal from a defect detector.
3. The method of claim 2 , wherein the defect signal is generated by obtaining a sum signal; obtaining a high pass filtered sum signal from the sum signal; indicating presence of the defect when the high-pass filtered sum signal exceeds a threshold value.
4. The method of claim 3 , wherein obtaining the sum signal includes receiving optical signals from at least one detector in an optical pick-up unit; calculating the sum of the optical signals.
5. The method of claim 1 , wherein detecting presence of the defect includes detecting a peak in the error signal.
6. The method of claim 5 , wherein the peak can be detected by low pass integrating the error signal to form an integration signal; indicating presence of the defect when the integration signal exceeds a threshold value.
7. The method of claim 1 , wherein detecting presence of the defect includes comparing the error signal between two cycles; and indicating presence of the defect when the difference between the error signal in the two cycles is greater than a threshold value.
8. The method of claim 7 , wherein the two cycles are consecutive cycles.
9. The method of claim 1 , wherein the error signal is a focus error signal.
10. The method of claim 9 , wherein generating the error signal includes: receiving optical signals from an optical pick-up unit with at least one detector, each of the at least one detector including a central element and two side elements; and calculating the difference between the sum of the optical signals from the two side elements and the optical signal from the central element.
11. The method of claim 1 , wherein the error signal is a tracking error signal.
12. The method of claim 11 , wherein generating the error signal includes: receiving optical signals from an optical pick-up unit with at least one detector, each of the at least one detector including a central element and two side elements; and calculating the difference between the optical signals from the two side elements.
13. The method of claim 1 , further including providing a count of the number of times that the low-pass filtered error signal is substituted for the error signal.
14. The method of claim 13 , wherein an error is indicated if the count is too high.
15. A method of calculating a control signal, comprising: receiving optical signals from an optical pick-up unit; generating an error signal from the optical signals; determining whether a defect criteria is present; substituting a low pass filtered error signal for the error signal if the defect criteria is present to generate an output signal; and generating the control signal from the output signal.
16. The method of claim 15 wherein the error signal is a focus error signal.
17. The method of claim 15 wherein the error signal is a tracking error signal.
18. The method of claim 15 , further including indicating an error position if the low-pass filtered error signal is substituted for the error signal a number of times exceeding an allowable number.
19. The method of claim 15 , wherein determining whether the defect criteria is present includes receiving a defect signal from a defect detector.
20. The method of claim 15 , wherein determining whether the defect criteria is present includes detecting a peak in the error signal.
21. The method of claim 15 , wherein determining whether the defect criteria is present includes comparing the difference between the error signal from a first cycle to the error signal from a second cycle with a threshold value.
22. The method of claim 21 , wherein the first cycle and the second cycle are adjacent cycles.
23. A servo system, comprising: an optical pick-up unit; at least one processor coupled to receive digitized optical signals from the optical pick-up unit, the processor calculating a control signal; and a driver coupled to control the position of the optical pick-up unit in response to the control signal, wherein the at least one processor executes an algorithm that generates an error signal; detects presence of a defect; and substitutes a low pass filtered version of the error signal for the error signal when the defect is detected.
24. The method of claim 23 , wherein presence of the defect can be detected by receiving a defect signal from a defect detector.
25. The method of claim 23 , wherein presence of the defect can be detected by detecting a peak in the error signal.
26. The method of claim 23 , wherein presence of the defect can be detected by comparing the error signal between two cycles; and indicating presence of the defect when the difference between the error signal in the two cycles is greater than a threshold value.
27. The method of claim 26 , wherein the two cycles are consecutive cycles.
28. The method of claim 23 , wherein the error signal is a focus error signal.
29. The method of claim 23 , wherein the error signal is a tracking error signal.