JPS605428A - Lens driving circuit of optical disk player - Google Patents

Abstract

PURPOSE:To obtain a lens driving circuit which is free from a lens shift error due to opening a servo loop by preventing the input voltage of a loop filter from being varied due to opening a signal line. CONSTITUTION:A sample/holding part 2 consists of a signal line opening switch SW2, a capacitor C and a buffer. A lens kick pulse is transmitted from an optical disk controller for temporary stop of a player as well as search of music. This kick pulse turns the switch SW2 off and is also applied to a lense drive amplifier 5 via an adder circuit 4. The amplitude of a tracking error signal is sometimes increased when the SW2 is opened since the transmission of said kick pulse has no relation with the disk revolving state. This amplitude value is held at a capacitor C, and therefore a sudden change of input voltage is never given to a loop filter 3 even with opening of the SW2. This avoid a lens shift error generated when a loop is opened by the SW2.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field In optical disc players, in order to pause or search for a song, the entire optical pickup is not moved, and only the lens is moved within a period of several seconds to about 10 seconds. The present invention relates to this lens drive circuit.

BACKGROUND ART In order to follow a track, a digital audio disc player or an optical video disc player is equipped with a servo loop that detects a tracking error in the radial direction and drives a lens. Therefore, in the case of the above-mentioned pause or song search, it is necessary to open the roof during that time. For this reason, conventionally, with a circuit configuration as shown in FIG. 1, a loop has been opened using a return pulse or an advance pulse, which is a lens movement signal from a control device such as a microcomputer. That is, the above pulse is detected by a pulse detection circuit, made into a pulse of a constant width by an integration circuit, and the switch SW+ is closed. In this way, the servo loop is opened, and the return pulse or advance pulse is directly guided as a lens kick pulse to the lens drive amplifier to move the lens to a predetermined position. After this moving time has elapsed, the switch SW1 is opened and the track following state is resumed. By the way, since the tracking error signal is due to the influence of mechanical eccentricity, etc., it has a low frequency component below the rotation period of 10 Hz, and the amplitude changes over time. On the other hand, a pulse input for temporarily stopping the optical hiccup or searching for a song occurs completely temporally unrelated to the above-mentioned tracking error signal. Therefore, in some cases, the switch SW1 may be closed at the moment when the tracking error signal is quite large. Since the input end of the loop filter is short-circuited by the switch SW1, a pulse having the same amplitude and opposite polarity as the tracking error signal at that moment is input to the loop filter. Since the above-mentioned pulse also drives the lens, the lens position shift due to this causes
Pause by return t, pulse or advance pulse.

There was a drawback that it was not possible to accurately move the lens in a predetermined manner to search for a song. In particular, when the track is temporarily stopped, the movement is one track, so there are many errors.

In the above circuit, the servo loop is opened by short-circuiting and grounding the input end of the loop filter, but the same situation applies if the input end of the loop filter is not grounded and one end is opened.

DISCLOSURE OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned drawbacks and to provide a lens drive circuit that is free from lens movement errors due to opening of a servo loop.

The lens drive circuit according to the present invention includes a sample/hold section consisting of a signal line open switch and a signal data hold circuit provided on the input side of a loop filter, and a lens drive amplifier, and operates the switch in response to a lens kick pulse signal. It is characterized by controlling and driving a lens driving amplifier.

According to the configuration of the present invention, when the switch opens the signal line due to the lens kick pulse, the tracking error signal at that time is held in the signal data hold circuit. Terminals do not fluctuate. Therefore, since the input voltage fluctuation of the lens drive amplifier is caused only by the lens kick pulse, the lens can be moved accurately in accordance with the pulse width of the lens kick pulse.

This makes it possible to reliably search for nine paused songs.

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 is a circuit block diagram showing one embodiment of the present invention. In this figure, 1 is a radial error detection circuit, 2 is a sample/hold section consisting of a signal line open switch SW2, a capacitor C, and a buffer, 3 is a loop filter, 4 is an adder circuit, and 5 is a lens drive amplifier.

In this circuit, when a lens kick pulse is sent from the optical disk controller to pause the player and search for a song, the pulse turns off the switch SW2 and is sent to the lens drive amplifier via the adder circuit 4. 5. The lens kick pulse is used as a lens kick pulse by triggering a monostable multivibrator using a return pulse or an advance pulse from a control device such as a microcomputer to output a pulse with a predetermined pulse width. The pulse width is set to an appropriate value for each case of pause and song search. Since the sending of the lens kick pulse is unrelated to the rotational status of the disk, the amplitude of the tracking error signal when the switch SW2 is opened may be large. However, switch SW2
Since the amplitude value is held by the capacitor C even after the switch SW2 is opened, a sudden change in the input terminal of the loop filter 3 does not occur due to the opening of the switch SW2. Therefore, the pulse that drives the lens is only the lens kick pulse inputted manually via the adder circuit 4, and no lens movement error occurs due to opening the loop with the switch SW2.

The circuit time constant of the sample/hold section is set in consideration of the duration of the lens kick pulse.

It is in the case of a pause that the servo loop opening is affected. In the case of searching for a song, even if the holding voltage tends to drop a little, it will automatically follow the song selection after the switch is closed. From the above, if the circuit time constant of the switch/hold section is set to a small value, the switch/hold section will hardly affect the open loop transfer function of the entire servo loop.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional lens driving circuit for searching and pausing music, and FIG. 2 is a block diagram of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Radial error detection circuit, 2...Sample/hold section, 3...Loop filter, 4...Addition circuit, 5...Lens drive amplifier, SWl, SW2...Switch. Patent applicant: ShinNippon Electric Co., Ltd. Agent Patent attorney: Akihiko Sato

Claims (1)

[Claims] The tracking servo loop of an optical disc player includes a sample/hold section consisting of a signal line open switch and a signal data bold circuit provided on the input side of the roof reel filter, and a lens drive amplifier, and the switch is activated in response to a lens kick pulse signal. A lens drive circuit for an optical disc player, characterized in that it drives a control circuit and a lens drive amplifier.