JPH0719455B2 - Tracking controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tracking control device, and more specifically, it irradiates a recording medium with detection light to form a light spot,
The present invention relates to a tracking control device that controls the relative position of the light spot with respect to the track based on the reflected light of the detection light from the recording medium.

[Outline of Invention]

In the tracking control device of the present invention, the change in the phase difference of the low frequency component is detected and stored in the pair of detectors, and the output gain of the detector is controlled in accordance with the change in the phase difference.

[Conventional technology]

FIG. 4 shows a block diagram of a conventional push-pull type tracking control device. Reference numerals 1 and 2 denote a pair of detectors arranged to detect the deviation of the information detection points in the direction orthogonal to the track, and are composed of light receiving elements in, for example, an optical video disc player. Reference numerals 3 and 4 denote low-pass filters, which extract low-frequency components from the outputs of the detectors 1 and 2. The outputs of the low-pass filters 3 and 4 are input to the differential amplifier circuit 7 after their gains are controlled by the automatic gain control circuits (AGC) 5 and 6, and a tracking error signal is generated from the difference. Tracking error signal is equalizer 8, loop switch 9, buffer amplifier circuit
It is supplied to the actuator 11 via 10. The actuator 11 biases, for example, an objective lens (not shown) in the direction orthogonal to the track to control the tracking of the light spot on the disk.

When the loop switch 9 is open and the light spot crosses the track due to eccentricity of the disk or the like, a phase difference occurs in the light received by the detectors 1 and 2. This is because there is a difference in the optical paths of the light reflected by the pits and the grooves on the track due to the difference in height between the pits and the grooves, and this optical path difference causes a phase difference in the light detected by the detectors 1 and 2. .

The light having this phase difference is detected by the detectors 1 and 2,
Low-pass filters 3 and 4 and automatic gain control circuit 5,
When input to the differential amplifier 7 via 6, the differential amplifier 7
Thus, a difference signal between the detectors 1 and 2, that is, a tracking error signal is obtained, the tracking error signal is input to the envelope detection circuit 12, and the envelope thereof is detected. The amplitude (envelope) of the tracking error signal is substantially proportional to the sensitivity of the detectors 1 and 2. Then, the envelope signal is input to the comparison circuit 13 and compared with a predetermined reference voltage output from the reference voltage generation circuit 14. The comparator circuit 13 outputs a low level signal to the counter 15 when the envelope amplitude is larger than the reference voltage and a high level signal when the envelope amplitude is smaller than the reference voltage. When the loop switch 9 is open, the switch 16 is closed and the clock output from the clock generation circuit 17 is supplied to the counter 15. The counter 15 counts up the clock when the comparison circuit 13 is at the high level, and counts down when the comparison circuit 13 is at the low level. As a result, the counter 15 outputs the number of clocks corresponding to the difference between the high level period and the low level period. A signal corresponding to this number is converted from a digital signal to an analog signal by the D / A conversion circuit 18 and supplied to the automatic gain control circuits 5 and 6 as a control signal. The automatic gain control circuits 5 and 6 control the amplitudes of the signals input from the flow pass filters 3 and 4 in accordance with the control signals. In this way, servo is applied so that the average level of the tracking error signal corresponds to the reference voltage (level).

When the loop switch 9 is closed and the tracking servo loop is opened, the switch 16 is opened. The counter 15 stores the output value immediately before the stop when the supply of the clock is stopped, and thereafter outputs the stored value.

[Problems to be solved by the invention]

In this way, the conventional tracking control device detects the level of the tracking error signal by detecting the envelope of the tracking error signal, and the detectors 1, 2 are detected.
The sensitivity (the level of the output signals of the detectors 1 and 2) was controlled. However, since the level of this tracking error signal changes depending on the depth of the pits or grooves on the track, the depth of the pits or grooves may change due to the deformation of the disk such as warpage or the shape of the pits or groups due to the variation of each disk. And the tracking error signal and the level may decrease. In this case, the envelope detection circuit 12 cannot detect the envelope accurately, which makes it impossible to perform accurate sensitivity adjustment.

An object of the present invention is to provide a tracking control device which can obtain a tracking error signal of an appropriate level even when there is a deformation of a disc such as a warp or a change in the shape of a pit or a groove due to a variation between discs. Especially.

[Means for solving problems]

In order to solve the above problems, the present invention irradiates a recording medium with detection light to form a light spot, and reflects the detection light from the recording medium at a position corresponding to the position of the light spot. In a tracking control device for controlling tracking of the light emission spot in the direction orthogonal to the track based on the above, a pair of detecting a reflected light from the recording medium at a position corresponding to the position of the light spot and outputting a detection signal to each pair. Detector, a differential amplifier circuit that generates a tracking error signal from a difference between detection signals of the pair of detectors, and a relative position of the light spot with respect to the track corresponding to the tracking error signal. An actuator that is biased in the orthogonal direction, a switch that controls the supply of the tracking error signal to the actuator, and a low band of each detection signal of the pair of detectors. A low-pass filter arranged with respect to the detector so as to extract the component, and a phase difference between each output of the low-pass filter caused by the groove or the uneven shape formed on the information recording surface of the recording medium is detected. Detection circuit,
A storage circuit that stores the phase difference when the switch does not supply the tracking error signal to the actuator, and a pair of detection signals of the detectors that correspond to the phase difference stored by the storage circuit. And a gain control circuit for controlling the gain of the.

[Action]

The low-pass component is extracted from the output signal of the detector by the low-pass filter arranged corresponding to the pair of detectors.
The phase difference of the low frequency component signal when the loop switch is open is detected and stored. When the loop switch is closed, the gain of the detector output signal is controlled in response to the stored phase difference.

〔Example〕

FIG. 1 is a block diagram of the tracking control device of the present invention. The parts corresponding to those in FIG. 4 are denoted by the reference numerals, and the detailed description thereof will be omitted. 21, 22 in FIG.
Are capacitors for removing the DC component from the output signals of the low-pass filters 3 and 4 and extracting only the AC component. Reference numerals 23 and 24 are comparator circuits for waveform-shaping the outputs of the capacitors 21 and 22, respectively. 25 is an exclusive OR circuit,
The exclusive OR of the outputs of the comparison circuits 23 and 24 is calculated and output. These constitute a detection circuit that detects the phase difference between the outputs of the low-pass filters 3 and 4. The output of the exclusive OR circuit 25 is integrated by the integration circuit 26 and then input to the A / D conversion circuit 27. A latch circuit 28 latches and stores the signal converted from the analog signal to the digital signal by the A / D conversion circuit 27. D / A
The conversion circuit 29 converts the output of the latch circuit 28 from a digital signal into an analog signal and inputs the analog signal into the comparison circuit 30. The comparison circuit 30 uses the signal from the D / A conversion circuit 29 as a reference voltage generation circuit 31.
And outputs the comparison result as a control signal to the automatic gain control circuits 5 and 6. Reference numeral 32 is a control circuit including a microcomputer or the like, which controls the loop switch 9 and the latch circuit 28.

Then, the control circuit 32 opens the loop switch 9 before starting the tracking servo operation. At this time, the disk is rotated, but since the center of the disk (track) and the center of rotation are generally not the same as in the case described above, the light spot crosses the track. As a result, high-pass components such as RF signals are removed from the output signals of the detectors 1 and 2 by the low-pass filters 3 and 4, the low-pass components that are the main components of the tracking error signal are extracted, and the capacitors 21, The signals from which the DC component has been removed by 22 are as shown in FIGS. 2 (a) and 2 (b), respectively.

Now, if the curves of these signals are approximated by sin θ and the phase difference between them is δ, the difference signal is sin (θ + δ / 2) −sin (θ−δ / 2) = 2sin (δ / 2) cosθ・ ・ It becomes (1). As is clear from the above equation, the sensitivity (amplitude) of this difference signal (when tracking control by the so-called push-pull method, this difference signal corresponds to the tracking error signal) is the sine sin (1/2) of the phase difference δ. proportional to δ / 2).
The sin (δ / 2) is shown in FIG. 3 when illustrated. As is clear from the figure, in the range where the value δ / 2 is sufficiently small, sin (δ / 2) ≈ δ / 2 (2), so that the equation (1) is eventually δcosθ ... (3) That is, the sensitivity of the tracking error signal is approximately proportional to the phase difference δ.

Here, the phase difference δ in the present embodiment changes due to a difference in optical path due to a change in the shape (particularly, the depth) of the pit or groove due to the deformation of the disk such as warpage or the variation among the disks.

The present invention is directed to a phase difference δ caused by a difference in optical path due to a change in the shape of pits or grooves (particularly, their depth) due to deformation of the disk such as warpage or variation between the disks.
By controlling the sensitivities of the detectors 1 and 2 in accordance with the change of (1), an appropriate tracking error signal is always obtained, and the tracking control can be stably performed.

From this viewpoint, the output signals of the capacitors 21 and 22 are compared circuits.
The signals are input to 23 and 24, respectively, and compared with a predetermined reference level (zero level) to be shaped into a rectangular wave signal as shown in FIGS. 2 (c) and 2 (d). This rectangular wave signal is further input to the exclusive OR circuit 25, and the phase difference between the two signals is detected as shown in FIG. 2 (e). Even if the frequencies of both signals fluctuate, the duty ratio of the output of the exclusive OR circuit 25 corresponds to the phase difference δ of both signals. That is, this duty ratio changes in accordance with the phase difference δ caused by the change in the shape (particularly, the depth) of the pit or the groove. The signal corresponding to the phase difference δ is input to the integrating circuit 26 and integrated (smoothed) into an analog signal corresponding to the phase difference. That is, the level of this analog signal changes in accordance with the phase difference δ caused by the change in the shape of the pit or groove (in particular, its depth). This analog signal is converted into a digital signal by the A / D conversion circuit 27 and then input to the latch circuit 28. The control circuit 32 outputs a control signal to the latch circuit 28 when the loop switch 9 is open, and latches (stores) the digital signal from the A / D conversion circuit 27.

The latch circuit 28 is a D / A conversion circuit 2 for the latched digital value.
8, and the D / A conversion circuit 29 converts this value into an analog signal again and outputs it to the differential amplifier circuit 30. Differential amplifier circuit 30
Is a predetermined reference voltage output from the reference voltage generation circuit 31 and D / A
The difference from the signal voltage from the conversion circuit 29 is calculated, and the automatic gain control circuits 5 and 6 output the control signal as a control signal corresponding to the change in the phase difference δ caused by the change in the shape (in particular, the depth) of the pit or groove. Output. The control circuits 5 and 6 change the average level of the input signals from the low pass filters 3 and 4 in accordance with the control signal. Therefore, the average level of the output signals of the automatic gain controls 5 and 6 is controlled to a predetermined level corresponding to the predetermined reference voltage set by the reference voltage generation circuit 31.

As a result, the input signals from the low pass filters 3 and 4 are
The tracking error signal having an appropriate value is obtained by being corrected in accordance with the change in the phase difference δ caused by the change in the shape of the pit or groove (in particular, its depth).

When the control circuit 32 closes the loop switch 9 and outputs a tracking error signal to the actuator 11 via the equalizer 8, the loop switch 9 and the buffer amplification circuit 10 to execute tracking servo, it outputs a control signal to the latch circuit 28. After that, the latched (stored) digital value is continuously output.

In the above description, the memory circuit is configured by the A / D conversion circuit 27, the latch circuit 28, and the D / A conversion circuit 29. However, the phase difference can be stored as an analog signal by using a sample hold circuit or the like. Is also possible. The present invention is applicable to a pre-groove portion (on the information recording surface) in an optical disc in which information is recorded by phase pits (an uneven shape formed on the information recording surface), a phase change optical disc, a dye disc, a magneto-optical disc, The present invention is also applicable to a tracking control device that controls tracking of a light spot by using the formed groove).

〔effect〕

As described above, according to the present invention, a recording medium is irradiated with detection light to form a light spot, and based on the reflected light of the detection light from the recording medium at a position corresponding to the position of the light spot. In the tracking control device for controlling the tracking of the light emission spot in the direction perpendicular to the track, a pair of detections that receive the reflected light from the recording medium at the position corresponding to the position of the light spot and output a detection signal to each of them. Amplifier, a differential amplifier circuit for generating a tracking error signal from a difference between detection signals of a pair of the detectors, and a relative position of the light spot with respect to the track in correspondence with the tracking error signal. Actuator, a switch for controlling the supply of the tracking error signal to the actuator, and a low-frequency component of each detection signal of the pair of detectors. A low-pass filter arranged to the detector so as to extract, and detection for detecting a phase difference between each output of the low-pass filter due to a groove or an uneven shape formed on the information recording surface of the recording medium. A circuit, a storage circuit that stores the phase difference when the switch does not supply the tracking error signal to the actuator, and a phase difference that corresponds to the phase difference stored by the storage circuit.
Since the gain control circuit for controlling the gain of the detection signal of the pair of detectors is provided, the sensitivity of the detector is automatically adjusted regardless of the change in the shape of the pit or groove (in particular, its depth). Can be controlled.

[Brief description of drawings]

FIG. 1 is a block diagram of a tracking control device of the present invention,
FIG. 2 is a waveform diagram thereof, FIG. 3 is a characteristic diagram thereof, and FIG. 4 is a block diagram of a conventional tracking control device. 1,2 …… Detector 3,4 …… Low-pass filter 5,6 …… Automatic gain control circuit 7 …… Differential amplifier circuit 8 …… Equalizer 9 …… Loop switch 10 …… Buffer amplifier circuit 11 …… Actuator 12 …… Envelope detection circuit 13 …… Comparison circuit 14 …… Reference voltage generation circuit 15 …… Counter 17 …… Clock generation circuit 18 …… D / A conversion circuit 23,24 …… Comparison circuit 26 …… Integration circuit 27 …… A / D conversion circuit 28 …… Latch circuit 29 …… D / A conversion circuit 30 …… Comparison circuit 31 …… Reference voltage generation circuit 32 …… Control circuit

Claims (1)

[Claims] 1. A recording medium is irradiated with detection light to form a light spot, and the light spot is orthogonal to the track based on the reflected light of the detection light from the recording medium at a position corresponding to the position of the light spot. In a tracking control device for controlling tracking in a direction, a pair of detectors for receiving reflected light from the recording medium at a position corresponding to the position of the light spot and outputting a detection signal to each of the detectors; A differential amplifier circuit that generates a tracking error signal from a difference between detection signals of a detector; an actuator that biases the relative position of the light spot with respect to the track in the direction orthogonal to the track in response to the tracking error signal; A switch for controlling the supply of the tracking error signal to the actuator, and a switch for extracting the low-pass component of each detection signal of the pair of detectors. A low-pass filter arranged with respect to the output device, a detection circuit for detecting a phase difference of each output of the low-pass filter due to a groove or an uneven shape formed on the information recording surface of the recording medium, and the switch. A storage circuit that stores the phase difference when the tracking error signal is not supplied to the actuator, and a gain of a pair of detection signals of the detectors corresponding to the phase difference stored by the storage circuit. A tracking control device comprising: a gain control circuit for controlling.