JPS63204519A - Servo circuit for perforating type additional optical disk - Google Patents

Abstract

PURPOSE:To obtain tracking servo gain at the same level by deciding whether a track is a written track or an unwritten track based on an RF signal and switching the gain of a circuit. CONSTITUTION:The automatic gain control (AGC) of a difference signal between two signals outputted from a detector 4 is executed by an AGC circuit 5 by using a sum signal so that servo gain is not changed by the reflection or the like of a disk. However the tracking servo gain is reduced in the written track of a perforating type additional writing optical disk, so that an RF signal is passed through a high-pass filter (HPF) 6 for 1kHz to cut out a DC component in order to correct the signal. The double wave rectification of said corrected signal is executed by a double wave rectifying circuit 7, the rectified signal is smoothed by a smoothing circuit 8 and the output signal from the circuit 8 is inputted to a gain switching amplifier 9 to change the amplification factor of the differential signal so that the tracking servo gain is fixed. Consequently, both the written track and unwritten track can obtain tracking servo gain with the same level.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a servo circuit for a write-once optical disc using a punching method.

(Prior art) Conventionally, in the case of the far-field detection method, the tracking error signal is obtained as a difference signal of the detector, and in order to prevent the servo gain from changing due to the reflectance of the recording medium, automatic gain control ( (hereinafter referred to as AGC).

(Problem to be Solved by the Invention) However, in the conventional method described above, the sum signal of the detector on the written track becomes small, and the difference signal becomes small even more, so the servo gain on the written track becomes small. There was a problem.

The present invention is intended to solve such conventional problems, and aims to obtain a servo gain on a written track that is at the same level as a servo gain on an unwritten track.

(Means for Solving the Problems) In order to achieve the above object, the present invention applies AGC and further determines whether the track is a written track using a data reproduction signal (hereinafter referred to as RF multiplied signal). A detector is provided, and an amplifier is connected after the AGC circuit to switch the gain according to the output signal of the detector, that is, a signal indicating whether the track is a written track or an unwritten track.

(Function) If the gain of the circuit is switched by determining from the RF signal whether it is a written 1-rack or an unwritten track, the tracking servo gain will be the same for both the written track and the unwritten track. You can get it by level.

(Example) The figure shows the configuration of an embodiment of the present invention.

1 is a recording medium, that is, a disk, which is rotated by a spindle motor 2; 3 is a pickup, which is controlled to be in focus on the track of the disk. A tracking servo is also applied to follow the track. The tracking error signal (TR signal) represents the amount of deviation from the track, and it is an object of the present invention to ensure that the servo gain thereof can always be obtained at a constant level. The difference signal between the two signals from the detector 4 is subjected to AGC by an AGC circuit 5 using a sum signal so that the servo gain does not change due to the reflectance of the disk or the like. However, in a write-once optical disc using the hole punching method, the tracking servo gain becomes small in the written track, so the correction is performed as follows. In other words, R■? The signal is passed through an IKI (z bypass filter (HPF)) 6 to cut the DC component, and then double-wave rectified by a double-wave rectifier circuit 7, passed through a smoothing circuit 8 for smoothing, and the output signal is subjected to gain gain. The tracking servo gain is kept constant by inputting it to the switching amplifier 9 and changing the amplification factor of the difference signal.

(Effects of the Invention) As is clear from the above embodiments, the present invention has the advantage that the same level of tracking servo gain can be obtained for both written and unwritten tracks in a write-once optical disc using a hole punching method. has.

[Brief explanation of the drawing]

The figure is a configuration diagram of an embodiment of the present invention. 1... Recording medium (i.e. disk), 2... Spindle motor, 3... Pickup, 4...
Detector, 5...AGC (auto gain control), 6...IKHz bypass filter,
7...Double wave rectifier circuit, 8...Smoothing circuit, 9...
...gain switching amplifier.

Claims (1)

[Claims] A servo circuit for a write-once optical disc using a punching method, characterized by comprising a circuit for detecting whether a track has been written or an unwritten track from a data reproduction signal, and an amplifier whose output changes the amplification gain of a tracking error signal.