Method and apparatus for reducing noise in a tracking error signal

• US 6,781,932 B2
• Filed: 05/29/2001
• Issued: 08/24/2004
• Est. Priority Date: 11/30/2000
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: LSI Logic Corporation (Broadcom, Inc.)
• Inventors: Beatson, Trevor P.
• Primary Examiner(s): HINDI, NABIL Z
• Application Number:
  US09/867,052
• Publication Number:
  US 20020064106A1
• Time in Patent Office: 1,183 Days
• Field of Search: 369/44.28, 369/44.27, 369/44.41, 369/44.42, 369/44.32
• US Class Current: 369/44.41
• CPC Class Codes: G11B 7/0901 for track following only G11B7/0925, G11B7/094, G11B7/0941, G11B7/0943, G11B7/0945, G11B7/0946, G11B7/0948 take precedence

Abstract

An apparatus (22) for reducing noise in a tracking error signal receives input signals from an array (5) of photodetectors, each input signal indicating the amount of laser light incident on the corresponding photodetector reflected from an optical disc. The input signals from diagonal pairs of photodetectors are summed and then filtered and digitized to produce a pair of digital input signals. A signal difference generator (20) produces first and second difference signals when either the first or the second digital input signals are received. The first and second difference signals are received by a programmable timing element having a user programmable device (41) and a signal limiting device (32, 33, 34, 35) for limiting the duration of the first or second difference signals provided at respective first or second outputs of the programmable timing element to a user programmable maximum value. The duration limited first or second difference signals are coupled to a charge pump (38) to provide a tracking error signal at an output.

Claims

1. A method of reducing noise in a tracking error signal, comprising the steps of:

(A) generating a first difference signal when a first digital input signal is received and a second difference signal when a second digital input signal is received;

(B) maintaining first or second charging signals while either the first difference signal or the second difference signal is detected;

(C) limiting the duration for which the first and second charging signals are maintained to a maximum duration; and

(D) generating a tracking error signal from the first and second charging signals.

2. The method according to claim 1, wherein each digital input signal is indicative of the amount of laser light incident on an optical detector reflected from an optical disk.

3. The method according to claim 1, wherein said maximum duration is programmable according to at least user defined criteria.

4. The method according to claim 1, further comprising:

(E) detecting when either the first difference signal or the second difference signal is generated.

5. The method according to claim 4, wherein step (E) further comprises:

XORing the first difference signal and the second difference signal to provide a detection signal.

6. The method according to claim 1, wherein step (C) further comprises:

generating a control signal when either the first difference signal or the second difference signal is detected;

limiting the generation of the control signal to a duration which is received from a user; and

combining the control signal with each of the first and second difference signals to maintain the first or second difference signals only while the control signal is generated.

7. The method according to claim 1, wherein step (C) further comprises:

automatically adjusted for a changing data rate in the received at least two digital input signals so as to maintain a predetermined phase difference between the at least two digital input signals.

8. The method according to claim 7, wherein the maximum duration is programmable by the user to change the predetermined phase difference.

9. The method according to claim 8, wherein the maximum duration is programmable by the user to adjust the predetermined phase difference according to how noisy the at least two digital input signals are so as to reduce noise on the tracking error signal.

10. The method according to claim 1, wherein the first and second digital input signals are generated from a 2×

2 array of four optical detectors, the first and second digital input signals being generated by summing output signals from diagonal pairs of optical detectors.

11. Apparatus for reducing noise in a tracking error signal, the apparatus comprising:

a signal difference generator having first and second inputs each coupled to respective one at least two digital input terminals, a first output for providing a first difference signal and a second output for providing a second difference signal;

a programmable timing element having first and second inputs coupled respectively to the first and second outputs of the signal difference generator and first and second outputs; and

a charge pump having first and second inputs coupled respectively to the first and second outputs of the programmable timing element to provide a tracking error signal at an output thereof.

12. The apparatus according to claim 11, wherein each digital input signal indicative of an amount of laser light incident on a corresponding optical detector reflected from an optical disc.

13. The apparatus according to claim 11, wherein the programmable timing element further includes a signal limiting device coupled to a user programmable device for limiting a duration of the first or second difference signals provided at the respective first or second outputs to a programmable maximum value.

14. The apparatus according to claim 11, wherein the programmable timing element comprises a detecting element having first and second inputs coupled respectively to the first and second outputs of the signal difference generator and an output to provide a signal indicating when either the first difference signal or the second difference signal is received.

15. The apparatus according to claim 14, wherein the detecting element comprises an XOR gate having a pair of inputs coupled to the outputs of the signal difference generator for receiving the first difference signal and the second difference signal and an output for providing a detection signal when either the first difference signal or the second difference signal is received.

16. The apparatus according to claim 15, wherein the programmable timing element comprises:

a control signal generator having a first input coupled to the output of the XOR gate, a second input coupled to the user programmable input, and an output for providing a control signal limited to a maximum duration; and

a combining element comprising a first portion having first and second inputs respectively coupled to the signal difference generator and a third input coupled to the output of the control signal generator and an output for providing the first or second difference signals as controlled by the control signal.

17. The apparatus according to any one of claim 16, wherein the programmable timing element comprises a further input for receiving a signal which automatically adjusts the maximum duration of the control signal for a changing data rate in the received at least two digital input signals so as to maintain a predetermined phase difference between the at least two digital input signals.

18. The apparatus according to claim 17, wherein the maximum duration of the control signal is programmable by the user to change the predetermined phase difference.

19. The apparatus according to claim 17, wherein the maximum duration is programmable by the user to adjust the predetermined phase difference according to how noisy the at least two digital input signals are so as to reduce noise on the tracking error signal.

20. The apparatus according to claim 11, wherein the at least two digital input signals are generated from a 2×

2 array of four optical detectors, the at least two digital input signals being generated by summing output signals from diagonal pairs of optical detectors.