Device for reading from and/or writing to optical recording media

• US 6,266,305 B1
• Filed: 06/03/1998
• Issued: 07/24/2001
• Est. Priority Date: 06/05/1997
• Status: Expired due to Fees

• Current Assignee: Deutsche Thomson-Brandt Gmbh (Vantiva SA)
• Original Assignee: Deutsche Thomson-Brandt Gmbh (Vantiva SA)
• Inventors: Büchler, Christian
• Primary Examiner(s): PSITOS, ARISTOTELIS
• Application Number:
  US09/090,045
• Time in Patent Office: 1,147 Days
• Field of Search: 369/44.32, 369/44.42, 369/124.13, 369/124.14
• US Class Current: 369/44.32
• CPC Class Codes: G11B 11/10576 with provision for moving the transducers for maintaining alignment or spacing relative to the carrier
• CPC Class Codes: G11B 7/0906 Differential phase difference systems
• CPC Class Codes: G11B 7/094 Methods and circuits for servo offset compensation
• CPC Class Codes: G11B 7/0956 to compensate for tilt, skew, warp or inclination of the disc, i.e. maintain the optical axis at right angles to the disc

Abstract

The present invention relates to a device for reading from and/or writing to optical recording media, which has a tracking unit, a four-quadrant detector, two summation points and a phase comparator for tracking in accordance with the differential phase detection method, and also two variable delay elements which can be set by a control unit. The device has improved compensation of the error in the track error signal and thus in the tracking signal. The error is caused by lens movement. An interference signal generating unit whose output is connected to the tracking unit and to a first input of the control unit, the second input of which is connected to the output of the phase comparator for providing error compensation.

Claims

1. A device for reading from or writing to optical recording media, said device comprising:

a tracking unit, a four-quadrant detector, two summation points and a phase comparator for tracking in accordance with the differential phase detection method;

a control unit;

at least three delay elements including two variable delay elements which can be set by the control unit;

an interference signal generating unit for generating an interference signal; and

a wobble synchronization signal generating unit for generating a wobble synchronization signal in response to the interference signal, the wobble synchronization signal being coupled to a first input of the control unit, a second input of the control unit being connected to the output of the phase comparator.

2. The device according to claim 1, wherein the wobble synchronization signal generating unit comprises a phase shifter for phase shifting the interference signal for generating the wobble synchronization signal.

3. The device according to claim 2, wherein:

the at least three delay elements includes first and second variable delay elements assigned to first and second detector elements, respectively, of the four-quadrant detector, and third and fourth delay elements having fixed delay time assigned to third and fourth detector elements, respectively.

4. The device according to claim 2, wherein the at least three delay elements includes four variable delay elements, a respective variable delay element being assigned to each of the detector elements of the four-quadrant detector, and a switching unit for connecting a detector element pair to a control output at which an output signal of the control unit is present.

5. The device according to claim 1, further comprising:

a switching unit for connecting two of the detector elements of the four-quadrant detector to a respective variable delay element.

6. The device according to claim 2, wherein:

the control unit has a comparison unit, to whose inputs the output signal of the phase comparator and the output signal of the interference signal generating unit are applied, and whose output signal serves for setting the variable delay elements.

7. The device according to claim 2, wherein:

the control unit has an offset determining unit, to whose input the output signal of the phase comparator is applied, and whose output signal serves for setting at least one of the variable delay elements.

8. The device according to claim 7, wherein:

at least one of the delay elements is arranged between a summation point for output signals of the detector elements of the four-quadrant detector and the phase comparator.

9. The device according to claim 8, wherein:

a respective delay element is assigned to the summation points and in that a switching unit is present for connecting one of the delay elements to the output of the offset determining unit.

10. The device according to claim 8, wherein:

a switching unit is present for inserting a delay element between one of the summation points and the phase comparator.

11. The device according to claim 2, wherein:

the control output at which an output signal is present is assigned a circuit block, which determines at least one of absolute value and sign of the signal present at the control output.

20. The device according to claim 2, wherein the at least three delay elements comprises first and second variable delay elements assigned to first and second detector elements, respectively, or to third and fourth detector elements, respectively, of the four-quadrant detector, and a third variable delay element assigned to a sum of the outputs of the first and third detector elements or to a second sum of the outputs of the second and fourth detector elements.

12. A device for reading from or writing to optical recording media on which information items in the form of pits forming a track can be recorded, said device comprising:

a light source for producing a light spot on the optical recording medium;

a tracking unit for displacing the light spot essentially perpendicular to the track;

a detector for detecting the light reflected from the optical recording medium, the detector having four detector areas, wherein a first detector area and a second detector area are separated from a third detector area and a fourth detector area by a line which is arranged essentially perpendicular to the track, and the first detector area and the fourth detector area are separated from the second detector area and from the third detector area by a line which is arranged essentially parallel to the track, and the first detector area being connected via a first variable delay element to a first summation point, whose other input is connected to the third detector area, and the second detector area being connected via a second variable delay element to a second summation point, whose other input is connected to the fourth detector area, and the outputs of the summation points being connected to a phase comparator, whose output signal is fed to a tracking regulator for regulating the tracking unit;

a control unit for setting the delay time being connected to the first variable delay element and to the second variable delay element in order to set their delay times;

an interference signal generating unit for generating an interference signal that is connected to the tracking unit; and

a wobble synchronization signal generating unit for generating a wobble synchronization signal in response to the interference signal, the wobble synchronization signal being coupled to a first input of a comparison unit, whose second input is connected to an output of the phase comparator, and whose output is connected to the output of the control unit.

13. The device according to claim 12, wherein the wobble synchronization signal generating unit comprises a phase shifter for phase shifting the interference signal for generating the wobble synchronization signal.

14. A method for setting the delay times of delay elements of a device for reading from and/or writing to optical recording media, which device as a tracking unit, the delay elements being arranged between detector elements of a 4-quadrant detector and a unit for determining a track error signal, comprising the steps of:

a) opening the tracking control loop;

b) feeding an interference signal to the tracking unit;

c) generating a wobble synchronization signal in response to the interference signal;

d) comparing the track error signal and the wobble synchronization signal with one another;

e) changing jointly the delay times of delay elements which are assigned to two neighbouring detector elements;

f) repeating step e) if components of the interference signal in the track error signal lie above a specific limit value;

g) turning off the interference signal; and

h) retaining the delay times.

15. The method according to claim 14, wherein the step of generating the wobble synchronization signal comprises phase shifting the interference signal to generate the wobble synchronization signal.

16. The method according to claim 14, wherein:

the interference signal is a periodic signal.

17. The method according to claim 15, wherein:

the frequency of the periodic signal is below a resonant frequency of the tracking unit.

18. The method according to claim 15, wherein:

step f) further comprises the steps;

F1) detecting the component of the interference signal in the track error signal and comparing said component to the respective component of step c),

F2) evaluating, from the result of the comparison, a value for the change of the delay times of selected delay elements which are assigned to two neighboring detector elements for jointly changing the respective delay times.

19. A method for setting the delay times of delay elements of a device for reading from and/or writing to optical recording media, which device has a tracking unit, the delay elements being arranged between detector elements of a 4-quadrant detector and a unit for determining a track error signal, comprising the following steps:

a) opening the tracking control loop;

b) feeding an interference signal to the tracking unit;

c) checking the track error signal for the presence of an offset;

d) changing the delay time of the delay element or elements which are assigned to two diagonally opposite detector elements if an offset is present;

e) repeating step d) if the value of the offset lies above a predetermined limit value;

f) turning off the interference signal; and

g) retaining the delay times.