JP2000030266A - Focus control circuit of disk player - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus control circuit of a disk player constituted so as to read out the signal recorded on a disk by an optical pickup. SOLUTION: This focus control circuit is provided with an RF signal level detection circuit 5 for detecting a level of an RF signal obtained from the optical pickup 1 and outputting a servo control signal for holding the former value in a focus servo circuit 4, when the level is lowered from a prescribed level, and is constituted so as to keep the former value holding operation of the focus servo circuit 4 for a prescribed time, when the servo control signal disappears.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a focus control circuit of a disk player configured to read out a signal recorded on a disk by a pickup.

[0002]

2. Description of the Related Art A disk player which performs a reproducing operation by reading out a signal from a disk on which information data such as music is recorded by a digital signal using an optical pickup has become widespread. One of them is a CD player.

[0003] Such a disc player is required to accurately focus a light beam emitted from an optical pickup on a signal surface of the disc, and therefore generally includes a focus servo circuit.

[0004]

In a disk player, an operation of reading a signal recorded on a disk is performed by focusing a light beam on a disk surface, and the focus control operation is performed by a focus servo circuit. It is configured to work. The focus control operation in such a disc player is configured to be performed by displacing the position of the objective lens based on a focus error signal obtained from a photodetector incorporated in the optical pickup.

In such a disk player, if the signal surface of the disk is damaged, the level of the reflected light from the disk changes greatly, so that the level of the focus error signal also changes greatly. The operation cannot be performed accurately. To solve such a problem, the level of an RF signal obtained from a photodetector is detected, and when the level is in a reduced state, as a control signal for performing focus servo,
A method of controlling the focus by an operation called a previous value hold for holding the signal input up to that time has been performed.

In such a device, when detecting the level of the RF signal, the detection signal has a threshold level, and therefore, the focus error signal used for the focus servo operation may be affected by scratches. There is a problem that the servo operation is adversely affected.

An object of the present invention is to provide a focus control circuit which solves such a problem.

[0008]

SUMMARY OF THE INVENTION The present invention provides a focus error signal output circuit for generating a focus error signal from a signal obtained from a photodetector incorporated in an optical pickup and outputting the signal, and a focus error signal output circuit. A focus servo that outputs a control signal to a focus coil drive circuit that supplies a drive signal to the focus coil to displace the objective lens in a direction to correct the focus error signal based on the focus error signal output from the error signal output circuit An RF signal for detecting a level of an RF signal obtained from the photodetector and outputting a servo control signal for holding the previous value to the focus servo circuit when the level is lower than a predetermined level; And a level detection circuit. The previous value holding operation of the focus servo circuit when the servo control signal which has been output from the RF signal level detecting circuit by an increase to a predetermined level or higher than the decrease condition disappears is obtained so as to maintain a predetermined time.

[0009]

FIG. 1 is a circuit diagram showing an embodiment of a disc player according to the present invention, and FIG. 2 is a signal waveform diagram for explaining the operation of the present invention.

In FIG. 1, reference numeral 1 denotes an optical pickup for reading a signal recorded on a disk, and a photodetector for converting light reflected from the disk into an electric signal and a focus for displacing an objective lens in the direction of the disk surface. A coil and the like are incorporated. 2 is a focus coil drive circuit for supplying a drive signal to the focus coil, and 3 is a focus error which generates a focus error signal from a signal obtained from a photodetector incorporated in the optical pickup 1 and outputs the signal. The signal output circuit 4 receives the focus error signal output from the focus error signal output circuit 3 and displaces the focus lens driving circuit 2 in a direction for correcting the focus error signal based on the signal. Is a focus servo circuit that outputs a control signal to the control terminal 4S, and when the H (high) level signal is applied to the control terminal 4S, the operation of maintaining the state of the signal for the servo operation that has been performed so far. That is, it is configured to perform the previous value hold operation.

An RF signal level detection circuit 5 receives an RF signal obtained from a photodetector incorporated in the optical pickup 1 and detects the level of the RF signal. It is configured to output an H level servo control signal to the output terminal 5A when the state is further lowered. Reference numeral 6 denotes a holding circuit that holds the level of the servo control signal output from the output terminal 5A of the RF signal level detection circuit 5 for a predetermined time after the output level of the output terminal 5A is inverted to the L (low) level. It comprises a buffer amplifier circuit 7, resistors 8, 9, a diode 10 and a capacitor 11.

Reference numeral 12 denotes an OR circuit to which a servo control signal output from an output terminal 5A of the RF signal level detection circuit 5 and a signal held by the holding circuit 6 are input. 4 is connected to a control terminal 4 </ b> S.

The present invention is configured as described above. Next, the operation of such a circuit will be described with reference to the waveform diagram shown in FIG. In a state where the signal recorded on the disk is normally read, the level of the RF signal obtained from the photodetector is high. The signal is being output. Therefore, since the L-level signal is applied to the control terminal 4S provided in the focus servo circuit 4, the focus servo circuit 4 is in a state of performing a normal focus servo operation.

In a state where the normal focus servo operation is performed, the focus servo circuit 4 operates based on the focus error signal output from the focus error signal output circuit 3, and the control output from the focus servo circuit 4 is performed. The signal is input to the focus coil drive circuit 2. When such a signal is input to the focus coil driving circuit 2, a signal for displacing the objective lens in a direction in which a focus error is corrected is supplied from the focus coil driving circuit 2 to the focus coil. A focusing control operation for focusing on the signal surface of the disk is performed. Therefore, a read operation of the signal recorded on the disk by the optical pickup 1 can be performed.

When the light beam reaches a flaw portion on the signal surface of the disk during the signal reading operation, the level of the RF signal is changed from the time point T1 to the time point T2 in FIG. At the same time, the level of the focus error signal greatly changes as shown in FIG.

In FIG. 2, T1 is a point in time when the level of the RF signal is reduced due to a scratch, and the output terminal 5A of the RF signal level detection circuit 5 provided to detect the level of the RF signal is connected to the output terminal 5A of FIG. As shown in (C), an H level servo control signal is output from time T1 to time T2. The H-level servo control signal output to the output terminal 5A of the RF signal level detection circuit 5 is at time T2,
That is, when the level of the RF signal exceeds a predetermined level, the signal disappears. However, the level of the servo control signal is held for a predetermined time by the operation of the holding circuit 6, so that the output terminal of the OR circuit 12 As shown in D), T3 from time T1
Until the time point, an H level signal is output.

As described above, the RF obtained from the photodetector of the optical pickup 1 due to the scratch on the disk.
When the signal level falls below a predetermined level from the time point T1 to the time point T2, an H-level servo control signal is output to the output terminal 5A of the RF signal level detection circuit 5 during this time. 4
, The H level servo control signal is applied to the control terminal 4S provided from the point T1 to the point T3. Therefore, the focus servo circuit 4 is in a state of performing the previous value holding operation from the time point T1 to the time point T3, and the output terminal of the focus servo circuit 4 is fixed to the value of the previous value as shown in FIG. The output control signal is output.

Since the above-mentioned control signal is output from the output terminal of the focus servo circuit 4 to the focus coil drive circuit 2, even if the focus error signal greatly changes due to the influence of scratches, the focus servo circuit 4 The influence on the operation can be reduced, and a stable focus servo operation can be performed.

In the present embodiment, the holding circuit 6 is connected to the resistor 8,
9, the circuit configuration can be variously changed. The holding circuit 6 is connected between the RF signal level detection circuit 5 and the focus servo circuit 4 as a circuit for holding a signal output from the RF signal level detection circuit 5 for a predetermined time. By providing an inversion circuit for outputting a control signal for a predetermined time when the level of the RF signal returns to a high level in 5, the input time of the servo control signal input to the focus servo circuit 4 can be extended by a predetermined time. .

[0020]

According to the present invention, the level of an RF signal obtained from a photodetector incorporated in an optical pickup is detected, and when the level is lower than a predetermined level, the focus servo circuit is controlled. An RF signal level detection circuit for outputting a servo control signal for holding the value is provided, and when the RF control signal output from the RF signal level detection circuit disappears due to a rise in the RF signal level from a lowered state to a predetermined level or more. Since the previous value hold operation of the focus servo circuit is maintained for a predetermined time, even if the level of the focus error signal greatly changes due to a scratch on the disk, the influence on the focus servo operation by the focus servo circuit can be reduced. As a result, stable focus servo operation can be performed. That.

Further, according to the present invention, the holding circuit for holding the servo control signal for a predetermined time is provided between the RF signal level detecting circuit and the focus servo circuit, so that the RF signal level detecting circuit and the focus servo circuit are integrated. An advantage is that an external circuit can cope with the case of being constituted by a circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a disc player according to the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of the present invention.

[Explanation of symbols]

 Reference Signs List 1 optical pickup 2 focus coil drive circuit 3 focus error signal output circuit 4 focus servo circuit 5 RF signal level detection circuit 6 holding circuit

Claims (2)

[Claims] 1. A disc player comprising an optical pickup which incorporates a photodetector for converting light reflected from a disc into an electric signal and a focus coil for displacing an objective lens in the direction of the disc surface, wherein the photodetector is provided. A focus error signal output circuit for generating a focus error signal from the obtained signal and outputting the focus error signal, and an object in a direction for correcting the focus error signal based on the focus error signal output from the focus error signal output circuit. A focus servo circuit that outputs a control signal to a focus coil drive circuit that supplies a drive signal to the focus coil to displace the lens; and detects a level of an RF signal obtained from the photodetector and sets the level to be higher than a predetermined level. When in the lowered state, An RF signal level detection circuit that outputs a servo control signal for holding the previous value to the focus servo circuit, and the RF signal level is output from the RF signal level detection circuit when the level of the RF signal rises from a lowered state to a predetermined level or more. A focus control circuit for a disc player, wherein a previous value hold operation of the focus servo circuit is maintained for a predetermined time when a servo control signal disappears. 2. A storage circuit for holding a servo control signal output from an RF signal level detection circuit for a predetermined time when the signal disappears is provided between the RF signal level detection circuit and a focus servo circuit. The focus control circuit according to claim 1.