JP2766149B2 - Optical disk tracking controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking control device used for an information recording / reproducing apparatus for an optical disk.

[0002]

2. Description of the Related Art Conventionally, when recording information on an optical disk or reproducing information from the optical disk, a laser beam is emitted from an optical pickup along a track formed on the optical disk. At this time, it is well known that two types of methods, namely, a three-beam method and a one-beam push-pull method, are used as a tracking method for causing the irradiation position of the laser beam to follow a track.

For tracking, for example, in the one-beam push-pull method, a tracking error signal TE and a tracking zero-cross signal T have a circuit configuration as shown in FIG.
ZC is being generated.

That is, in FIG. 2, reference numeral 10 denotes an optical pickup, and as a photodetector 11 for receiving light reflected from an optical disk, a well-known four-divided photodetector 1 is used.
1 is used. Voltages V1 and V2 corresponding to the total amount of light received by detectors 11a and 11d located on the left side of the track and the total amount of light received by detectors 11b and 11c located on the right side of the track are generated by adder amplifiers 21 and 22, and these voltages V1 and V2 are generated. , V2 is the read signal (RF
The signal is output from the adder 23 as a signal. Further, a voltage V3 which is a difference between the voltages V1 and V2 is generated by the subtractor 24,
This voltage V3 is output as tracking error signal TE. Furthermore, the comparator 25 compares the voltage V3 of the tracking error signal TE with a predetermined reference voltage Vth (for example, 0 potential) to generate a binarized tracking zero cross signal TZC.

The tracking error signal TE and the tracking zero cross signal TZC thus generated are used for track jump, thread control, spindle control, etc. In particular, in a track jump, a brake pulse is generated using the tracking zero cross signal. Many methods are adopted.

[0006]

However, in the above-described conventional tracking control device, the offset of the tracking error signal TE often changes due to eccentricity of the optical disk, skew (SKEW), changes in the ambient temperature, and the like. I have. For this reason, it was very difficult to generate an accurate tracking zero cross signal TZC. For example, when the offset of the tracking error signal TE is slightly shifted, as shown in FIG.
When the duty of the tracking zero-cross signal TZC changes and the offset of the tracking error signal TE deviates significantly from the normal case of FIG.
As shown in (c), a tracking zero-cross signal TZC in which the zero-cross timing cannot be detected is obtained. For this reason, there has been a problem that an accurate track jump cannot be performed and a malfunction occurs.

An object of the present invention is to provide a tracking control apparatus for an optical disk capable of always generating an accurate tracking zero-cross signal in view of the above problems.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention detects reflected light from an optical disk on which information is recorded / reproduced using a two-part photodetector,
A tracking error signal and a tracking zero-cross signal generated from the detection result; and an optical disk tracking control device for controlling a laser beam irradiation position on the optical disk based on the tracking error signal and the tracking zero-cross signal. A gain variable circuit that changes the level of a signal output from the photodetector based on a control signal and outputs the same, a level of a signal output from the other photodetector of the two-divided photodetector, and a level of an output signal of the gain variable circuit A subtraction circuit that outputs a signal having a level of a difference from the tracking error signal as a tracking error signal; a first low-pass filter that outputs only a frequency component equal to or lower than a predetermined frequency in the tracking error signal as the control signal; A second low-pass filter that outputs only a frequency component equal to or lower than a predetermined frequency in the king error signal; comparing a signal level output from the second low-pass filter with a level of the tracking error signal; And a comparison circuit that outputs a tracking zero-cross signal based on the tracking control device.

[0009]

According to the present invention, the level of a signal output from one of two split photodetectors for receiving reflected light from an optical disk on which information is to be recorded / reproduced is changed by a gain variable circuit based on a control signal. The subtraction circuit outputs a signal having a difference between the level of the signal output from the other photodetector of the two-divided photodetector and the level of the output signal of the gain variable circuit as a tracking error signal. The first low-pass filter outputs only a frequency component equal to or lower than a predetermined frequency in the tracking error signal as the control signal. Since the control signal output from the first low-pass filter substantially becomes an offset component in the tracking error signal, the level of the signal output from the one photodetector is controlled by the control signal, whereby the tracking error signal is controlled. Is reduced. Furthermore, the second
By the low-pass filter described above, only the frequency component equal to or lower than a predetermined frequency in the tracking error signal is output.
Similarly, the output signal of the second low-pass filter is substantially an offset component in the tracking error signal, and the level of the signal output from the second low-pass filter is compared with the level of the tracking error signal. The signals are compared by a circuit, and a tracking zero-cross signal based on the comparison result is output.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a main part in one embodiment of the present invention, that is, a part relating to generation of a tracking zero cross signal. In the figure, the same components as those of the above-described conventional example are denoted by the same reference numerals. That is, 10 is an optical pickup using the one-beam push-pull method, 21 and 22 are addition amplifiers, 23 is an adder, 30 is a tracking error detection unit, and 40 is a tracking zero cross detection unit.

The optical pickup 10 includes a well-known four-divided photodetector 11, and performs tracking correction using the total amount of light received by detectors 11a and 11d located on the left side of the track and the total amount of light received by detectors 11b and 11c located on the right side of the track. And the total amount of light received by the detectors 11a and 11c on the diagonal line and the detectors 11b and 1c.
Focus correction can be performed by the astigmatism method or the like using the total received light amount of 1d.

The summing amplifier 21 receives the voltages output from the photodetectors 11a and 11d of the optical pickup 10 and outputs a voltage V1 obtained by adding the voltages. The summing amplifier 22 outputs the voltage V1 of the photodetectors 11b and 11d.
11c, and outputs a voltage V2 obtained by adding them. The adder 23 outputs the voltages V1, V
2 are input, added, and output as a read signal (RF signal).

The tracking error detector 30 includes a triangular wave generator 31, an adder 32, a comparator 33, and an electronic switch 3.
4. It comprises low-pass filters 35 and 36 and a subtractor 37. Voltage V1 output from summing amplifier 21
The voltage value is changed to a predetermined value by a variable gain circuit 38 including a triangular wave generator 31, an adder 32, a comparator 33, an electronic switch 34, and a low-pass filter 35, and is input to a subtractor 37 as a voltage V3. You. At this time, the voltage value is changed based on the offset correction voltage Vof output from the low-pass filter 36.

That is, the voltage V1 is the first voltage of the electronic switch 34.
Is input to the contact 34a. Further, the electronic switch 34
The second contact 34b is grounded, and the contact piece 34c is connected to the input terminal of the low-pass filter 35. Further, the electronic switch 34 controls the control voltage Vse output from the comparator 33.
When the control voltage Vse is high, the contact 34c is connected to the second contact 34b, and when the control voltage Vse is low, the contact 34c is connected to the first contact 34a.

The subtracter 37 receives the voltage V3 and the voltage V2, and outputs a voltage corresponding to the difference between the voltage V3 and the voltage V2 as a tracking error signal TE. The tracking error signal TE is input to the low-pass filter 36, and only a frequency component having a predetermined frequency, for example, 40 KHz or less, is extracted and output as the above-described offset correction voltage Vof.

As a result, the offset correction voltage Vof output from the low-pass filter 36 is added to the triangular wave voltage V4 output from the triangular wave generator 31 by the adder 32, and is added as a voltage V5 to the non-inverting input terminal of the comparator 33. Is entered. The voltage V5 is compared with a predetermined threshold voltage Vth1 by the comparator 33, and the control voltage Vse output from the comparator 33 becomes a high level when the voltage V5 is higher than the threshold voltage Vth1. It becomes low level when the threshold voltage Vth1 or less.

Here, the frequency of the triangular wave voltage V4 output from the triangular wave generator 31 is set to be at least ten times the signal frequency included in the voltage V1. As a result, the pulse width of the control voltage Vse is changed in accordance with the level of the offset correction voltage Vof, and the electronic switch 34 is switched accordingly, so that the voltage V6 input to the low-pass filter 35 is equal to the voltage V1. It will be intermittent. When the high-frequency component of the voltage V6 is removed by the low-pass filter 35, the output voltage V3 is smoothed, and the level changes according to the pulse width of the control voltage Vse. Accordingly, a tracking error signal TE with reduced offset is generated.

The tracking zero-cross detector 40
Is composed of a comparator 41 and a low-pass filter 42. The low-pass filter 42 receives the tracking error signal TE and passes only a low-frequency component thereof, for example, a voltage Va of a frequency component of 10 KHz or less. Thereby, only the offset component in the tracking error signal TE is extracted. The comparator 41 receives the voltage Va output from the low-pass filter 42 and the tracking error signal TE, compares the voltage of the tracking error signal TE with the voltage Va, and outputs a tracking zero-cross signal TZC. You.

Therefore, as shown in FIG. 4, even when the offset of the tracking error signal TE changes due to the eccentricity of the optical disk, the skew, the change in the ambient temperature, or the like, or when the offset is deviated, the comparator 41 performs the same operation. Since the voltage Va serving as the comparison reference also changes in accordance with the offset of the tracking error signal TE, the duty of the tracking zero-cross signal TZC does not change or the timing of the zero-cross cannot be detected. The signal TZC can be obtained. As a result, it is possible to stabilize the track jump, stabilize the spindle servo at the time of tracking off of the wobble method, and to prevent the flow of the thread, thereby performing the stable tracking control without malfunction.

[0020]

As described above, according to the present invention, a tracking error signal having a reduced offset component is generated, and the offset component of the tracking error signal is compared with the level of the tracking error signal to obtain a tracking zero-cross signal. Is generated, the eccentricity of the optical disc,
Even if a skew (SKEW), a change in ambient temperature, or the like occurs, an accurate tracking zero-cross signal is always obtained. As a result, malfunctions such as track jumps can be prevented,
This is a very excellent effect that stable tracking control can be performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a main part of an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a main part of a conventional example.

FIG. 3 is a diagram illustrating a problem of a conventional example.

FIG. 4 is a diagram for explaining the operation of an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Optical pick-up, 11a-11d ... Photodetector, 30 ... Tracking error detection part, 21 ... 22 Addition amplifier, 23 ... Adder, 31 ... Triangle wave generator, 32 ...
Adder, 33: comparator, 34: electronic switch, 35, 3
6 low-pass filter, 37 subtractor, 38 variable gain circuit, 40 tracking zero-cross detector, 41
Comparator, 42 ... Low-pass filter.

Claims (1)

(57) [Claims] 1. A method for detecting reflected light from an optical disk as an information recording / reproducing object using a two-segment photodetector,
A tracking error signal and a tracking zero-cross signal generated from the detection result; and an optical disk tracking control device for controlling an irradiation position of the laser beam on the optical disk based on the tracking error signal and the tracking zero-cross signal. A variable gain circuit that changes the level of a signal output from the photodetector based on a control signal and outputs the same, a level of a signal output from the other photodetector of the two-divided photodetector, and a level of an output signal of the variable gain circuit A subtraction circuit that outputs a signal having a level of a difference from the tracking error signal as a tracking error signal; a first low-pass filter that outputs only a frequency component of a predetermined frequency or less in the tracking error signal as the control signal; A second low-pass filter that outputs only a frequency component equal to or lower than a predetermined frequency in the racking error signal; comparing a signal level output from the second low-pass filter with a level of the tracking error signal; A tracking circuit for outputting a tracking zero-cross signal based on the tracking signal.