JPS62298933A - Tracking servo circuit for optical disc device - Google Patents

Abstract

PURPOSE:To easily eliminate an offset component by providing a low pass filter to obtain a voltage corresponding to the extent of displacement of an objective lens and providing a feedback circuit which eliminates the DC offset component due to displacement of the objective lens. CONSTITUTION:A tracking error detecting circuit 1 consists of a two-divided photodetector and a differential amplifier, and a tracking error detection signal e(x) of the tracking error detecting circuit 1 is inputted to the + terminal of a subtractor 2. The subtractor 2 constitutes a feedback circuit 5 together with a low pass filter 3 and an amplifier 4, and this feedback circuit 5 has a function to eliminate the offset component included in the tracking error detection signal e(x).

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention provides a method for driving an actuator based on a tracking error detection signal output from a tracking error detection circuit having a two-split light receiving element. Drives the drive circuit of
The present invention relates to an improvement in a tracking servo circuit for a so-called push-pull type optical disc device in which the objective lens follows the tracking direction of an optical disc.

(Prior Art) Conventionally, a so-called push-pull type optical disc tracking servo circuit as shown in FIG. 5 has been known. In FIG. 5, 20 is a tracking error detection circuit that outputs a tracking error detection signal e (x), 21 is a phase compensation circuit, 2z is a voltage feedback type drive circuit that outputs a drive signal K for driving the actuator, and 23 6 is an optical pickup having a tracking coil 25 for following and displacing the objective lens 24 shown in FIG.

The tracking error detection circuit 20 includes a two-split light receiving element 26 and a differential amplifier amblifier 2, as shown in FIG.
It consists of 7. This two-split light receiving element 26 has light receiving parts 26a and 26b, and as shown in FIGS. 6 and 8, the optical axis 0□ of the objective lens 24 is located at the center of the pit 29 (track center) of the optical disc 28. 6, the spot S of the light beam is located at pit 2.
As shown in FIGS. 7 and 8, images of the light beams are formed symmetrically on each of the light receiving sections 26a and 26b, and the light receiving state is symmetrical. Become. At that time, the amplitude of the tracking error detection signal e (x) is zero. Note that in FIGS. 7 and 8, hatched areas A and B schematically indicate brightly shining areas on the light receiving sections 26a and 26b, and in FIG. is the direction in which it extends.

Due to some adjustment, for example, eccentricity of the optical disc 28, the optical disc 28 is displaced in the disc radial direction (direction of arrow E) as shown by the broken line in FIG. 8, and the position of the spot S of the light beam relative to the pit 29 is If the tracking error is shifted, as shown in FIG. 9, the light receiving states of the light receiving sections 26a and 26b become asymmetrical, and a tracking error detection signal e(X) is output. The drive circuit 22 outputs a drive signal K based on the tracking error detection signal a (x), and the tracking coil 25 is energized so that the objective lens 24 follows the displacement of the optical disk 28. A servo is applied to. At this time, the objective lens 24 is displaced in accordance with the displacement frequency characteristic with respect to the frequency of the drive signal.

(Problem to be Solved by the Invention) By the way, suppose that at time ti, a servo is applied to the objective lens 24 and the optical axis 01 of the objective lens 24 is displaced so as to coincide with the center of the pit 29 ( 8th
(See the objective lens 24 indicated by the two-dot chain line in the figure). Then, as shown in FIG. 10, the light receiving states of the light receiving parts 26a and 26b of the two-split light receiving element 26 become bilaterally symmetrical, but the central optical axis 0. When the optical axis 01 of the objective lens 24 is biased, the output light amount distribution P of the light beam is biased, and even though the light receiving areas of the light receiving sections 26a and 26b are equal on the left and right sides, the difference in illuminance causes each light receiving section to be biased. Since the light receiving outputs of the sections 26a and 26b are different, the tracking error detection signal e(x) becomes the offset signal O.
Output as F. Since this offset signal OF is output, the drive circuit 22 outputs the drive signal K based on the offset signal OF, so that after time t0, the outputs of the left and right light receiving sections 26a and 26b match. As shown in FIGS. 11 and 12, the objective lens 24 is displaced, and as shown in FIGS. A servo is applied to the objective lens 24 so that the received light output becomes zero as a result. The amplitude of this offset signal OF is determined by the distance between the objective lens 2 and the center optical axis 02 of the output light amount distribution P of the light beam.
The more the optical axis 0□ of the lens 4 is shifted, the larger the shift becomes, and it is proportional to the amount of displacement of the objective lens 24.

In this way, the tracking servo circuit of the conventional so-called push-pull type optical disk device.

Since a DC offset component based on the displacement of the objective lens 24 is included, there is a drawback that the objective lens 24 cannot accurately follow the displacement of the optical disk 28 in the tracking direction.

(Objective of the Invention) Therefore, an object of the present invention is to eliminate the offset component that occurs based on the displacement of the objective lens when only the objective lens is driven and a tracking servo is applied to the objective lens in a so-called push-pull type optical disk device. It is an object of the present invention to provide a tracking servo circuit for an optical disk device that can be removed with a simple circuit configuration.

(Means for Solving the Problems) A tracking servo circuit of an optical disc device according to the present invention includes a tracking error detection circuit having a two-split light receiving element that receives irradiation light of a light beam irradiated onto an optical disc via an objective lens. A drive circuit for driving an actuator generates a drive signal for driving an actuator based on a tracking error detection signal output from the circuit. It is characterized in that it has a low-pass filter and is provided with a feedback circuit that removes a DC offset component caused by the displacement of the objective lens.

(Function) According to the tracking servo circuit of the optical disk device according to the present invention, if the optical axis of the objective lens deviates from the track due to some adjustment, the light receiving state of the two-split light receiving element changes, and the tracking error detection circuit detects the tracking error. An error signal is output. The drive circuit for driving the actuator outputs a drive signal for driving the actuator based on the tracking error detection signal. As a result, the objective lens is displaced in a direction that follows the displacement of the optical disk, according to the displacement frequency characteristics of the objective lens with respect to the frequency of the drive signal, and a tracking error detection signal containing an offset component based on the displacement is output to the drive circuit. However, the low-pass filter generates a displacement-corresponding voltage corresponding to the amount of displacement of the objective lens based on the drive signal, and this displacement-corresponding voltage is fed back, so the offset included in the tracking error detection signal components are removed.

(Example) Hereinafter, an example of a tracking servo circuit for an optical disc device according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of a tracking servo circuit for an optical disc device according to the present invention, and this first embodiment shows a constant voltage drive type. This first
In the figure, 1 is a tracking error detection circuit,
The tracking error detection circuit 1 is composed of a known two-part light receiving element 26 and a differential amblifier 27. The tracking error detection signal e (x) of the tracking error detection circuit 1 is input to a child terminal of the subtracter 2 . This subtracter 2 is a low-pass filter 3
, and amplifier 4 constitute a feedback circuit 5, which has a function of removing an offset component included in the tracking error detection signal e(x).The output of the subtracter 2 is as follows: The signal is inputted to a voltage feedback type drive circuit 7 via a phase compensation circuit 6. This drive circuit 7 outputs a drive signal K toward a tracking coil 8 for driving the objective lens.

The tracking coil 8 constitutes a part of an actuator (not shown) for driving the objective lens, and the actuator is mounted on the optical pickup 9.

Based on the energization of the tracking coil 8, the objective lens 24 is displaced to follow the displacement of the optical disk 28 according to the displacement frequency characteristic shown in FIG. 2, which shows the amount of displacement of the objective lens 24 with respect to the frequency of the drive signal. be.

The low-pass filter 3 has a gain frequency characteristic corresponding to the displacement frequency characteristic of the objective lens 24, as shown in FIG. The drive signal of the drive circuit 7 is fed back to the low-pass filter 3. The low-pass filter 3 has a displacement corresponding voltage Q corresponding to the amount of displacement of the objective lens 24 which is displaced according to the frequency based on the drive signal K.
This displacement corresponding voltage Q is input to one terminal of the subtracter 2 via an amplifier 4. Subtractor 2 is
It has a function of removing the DC offset signal OF included in the tracking error detection signal e(x), and the amplitude (voltage) of the DC offset signal OF is proportional to the amount of displacement of the objective lens 24, and Since the amount of displacement of the lens 24 is determined by the drive signal K, if the displacement corresponding voltage Q is obtained based on this drive signal K, the displacement corresponding voltage Q will be one pair with the amount of displacement of the objective lens 24. If the displacement corresponding voltage Q is appropriately amplified by the amplifier 4, the offset component included in the tracking error detection signal e(x) can be removed. Note that in FIGS. 2 and 3, fo is a resonant frequency, and in a frequency region higher than the resonant frequency, it is attenuated at 12 dB/octave.

FIG. 4 is a diagram showing a second embodiment of a tracking servo circuit for an optical disc device according to the present invention, and this second embodiment is a diagram in which the present invention is applied to a tracking servo circuit for a constant current type optical disc device. There is no difference from the first embodiment except that the feedback circuit 5 is constructed by feeding back the voltage of the resistor 10 forming a part of the current-type feedback circuit to the low-pass filter 3 as a drive signal.

Identical components are given the same reference numerals and detailed explanations thereof will be omitted.

(Effects of the Invention) As explained above, according to the present invention, the tracking error detection circuit having a two-split light receiving element that receives the irradiation light of the light beam irradiated onto the optical disc through the objective lens a low-pass filter for obtaining a displacement corresponding voltage corresponding to the amount of displacement of the objective lens based on a drive signal of a drive circuit for driving the actuator that generates a drive signal for driving the actuator based on the tracking error detection signal; Since a feedback circuit is provided to remove the DC offset component caused by the displacement of the objective lens, the offset component generated in the tracking error detection signal due to the displacement of the objective lens can be removed with a simple circuit configuration. .

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram showing a first embodiment of the tracking servo circuit of an optical disc device according to the present invention, FIG. 2 is a displacement frequency characteristic diagram showing the amount of displacement of the objective lens with respect to the frequency of the drive signal, and FIG. FIG. 4 is a gain frequency characteristic diagram of the low-pass filter according to the present invention, and FIG. 4 is an equivalent circuit diagram showing a second embodiment of the optical disc device according to the present invention, and FIGS.
The figure is a diagram for explaining a malfunction of a tracking servo circuit of a conventional optical disc device, and FIG. 5 is an equivalent circuit diagram of a tracking servo circuit of a conventional optical disc device.
FIG. 6 is a diagram showing a state in which the optical axis of the objective lens is positioned at the center of the pit of the optical disc, and a circular spot of the light beam is formed symmetrically on the optical disc.
The figure schematically shows the image formed on the two-split light-receiving element when the circular spot shown in Figure 6 is formed, and Figure 8 shows the optical disc oriented in the radial direction of the disc with respect to the optical axis of the objective lens. Explanatory diagram 5 for explaining the displaced state Figure 9 is a diagram schematically showing an image formed on the two-split light receiving element when the optical disc is displaced in the disc radial direction, Figure 10
The figure is a diagram for explaining the image formed on the light-receiving part of the two-split light-receiving element when the objective lens is displaced based on the displacement of the optical disc in the disk radial direction. FIG. 12 is a diagram for explaining a state in which the tracking error detection signal is offset to a position where it becomes zero based on the displacement, and is a schematic diagram showing the light receiving state of the two-split light receiving element at that time. 1...Tracking error detection circuit 2...Subtraction circuit 3...Low pass filter 5...Feedback circuit 7...Drive circuit 24...Objective lens 26...Two-split light receiving element 28... Optical disk Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Procedure amendment (voluntary) March 9, 1986

Claims (1)

[Claims] (1) Drive for driving an actuator by having a two-split light receiving element that receives the irradiation light of the light beam irradiated onto the optical disc through an objective lens, and transmitting a tracking error detection signal based on the light receiving state of the two-split light receiving element. a tracking error detection circuit that outputs a tracking error detection circuit to a circuit, causes the drive circuit to output a drive signal based on the tracking error detection signal, and moves the objective lens in the tracking direction of the optical disk according to the displacement frequency characteristic with respect to the frequency of the drive signal. The tracking servo circuit of the optical disk device for tracking includes a low-pass filter for obtaining a displacement-corresponding voltage corresponding to the amount of displacement of the objective lens based on the drive signal, and the circuit includes a low-pass filter for obtaining a displacement-corresponding voltage corresponding to the displacement amount of the objective lens, and eliminates a DC offset component caused by the displacement of the objective lens. A tracking servo circuit for an optical disc device, comprising a feedback circuit for removing the feedback.