JPH01144251A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To exactly detect drop-outs distributed in an adjacent band to an FM carrier frequency as well by detecting pulse-like noises out of a signal being reflected in reflectance ratio on a groove of a magneto-optical disk. CONSTITUTION:By adding up signals outputted from pin diodes 11 for detecting a signal of a magneto-optical pickup with an adder amplifying circuit 17, the signal reflected in reflectance ratio on the groove of the magneto-optical disk is obtained, and the pulse-like noises generating on this signal are detected, and moreover a criterion value of such a pulse-like noise is taken as (1+ or -alpha) times (provided that alpha=0.2-0.25) as much as the mean value of the reflectance ratio on the groove, so as to carry out the detection with a voltage comparator 19. By this method, small drop-outs distributed also in the vicinity of the FM carrier frequency can exactly be detected out, thus enabling the excellent correction of the drop-out.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical recording and reproducing apparatus for recording, reproducing and erasing video signals on a magneto-optical disk using a magneto-optical effect as a recording principle.

2. Description of the Related Art In recent years, an optical recording/reproducing device 1 using a magneto-optical disk has been expected to serve as an erasable large-capacity optical memory.

In particular, applied research is being actively conducted on mass storage for storing huge amounts of image data.

An example of the conventional optical recording/reproducing apparatus described above will be described below without reference to the drawings.

FIG. 3 shows a block diagram of a conventional optical recording/reproducing device. In Fig. 3, 1 is a binfo I for signal detection.
・Diode, 2 is a differential amplifier, 3 is a band pass filter, 4 is an auto gain control circuit, 5 is a video signal demodulation circuit, 6 is a dropout correction circuit, 7 is an envelope detection circuit, and 8 is a voltage comparator.

The operation of the optical recording/reproducing apparatus configured as described above will be explained below.

First, a signal output from a signal detection pin photodiode 1 of a magneto-optical pickup is differentially amplified by a differential amplifier 2 to obtain a reproduced RF signal. This reproduced RF signal is processed by bandpass filter 3 to a frequency of approximately 10KHz to IOM.
The band is limited to Hz, and the amplitude is kept constant by the auto gain control circuit 4. The output of the auto gain control circuit 4 is demodulated by the video signal demodulation circuit 5 to obtain a video signal. However, if there are omissions or defects in the reproduced RF signal obtained from the differential amplifier 2,
When demodulated into a video signal, dropouts occur and have an adverse effect. Conventionally, the envelope of the reproduced RF signal is detected by an envelope detection circuit 7, and the drop in the voltage level is further detected by a voltage comparator 8, as shown in FIG.

The detected omissions and defects in the reproduced RF signal are sent to the dropout correction circuit 6, which maintains the previous value of the video signal.
Dropouts were corrected by means such as H interpolation.

Problems to be Solved by the Invention However, in the above configuration, the dropout detection ability is highly dependent on the state of the envelope detection circuit 7, and therefore sufficient dropout correction cannot be performed. In other words, if an envelope detection circuit is used to detect dropouts, if the reproduced RF signal has large omissions or defects, specifically, if there are more than 5 to 10 bits of the carrier wave, it will be possible to accurately detect the omissions. However, if the missing bit is as small as 1 to 5 bits, the envelope detection circuit integrates the input signal and
Due to the nature of detecting the envelope line.

This poses a problem in that detection becomes difficult and dropout correction cannot be performed properly.

In view of the above-mentioned problems, the present invention provides an optical recording and reproducing apparatus that can appropriately correct dropouts even for small dropouts distributed in a band near the carrier frequency.

Means for Solving the Problems In order to solve the above-mentioned problems, the optical recording/reproducing device of the present invention includes a magneto-optical pickup equipped with a differential optical system that records, reproduces, and erases signals by magneto-optical effects; Two signals are output from this magneto-optical pickup and have a phase difference of 180 degrees.
A differential amplifier that differentially amplifies two reproduction signals, a bandpass filter that limits the band of the output signal of this differential amplifier, an auto gain control circuit that keeps the amplitude of the output signal of this bandpass filter constant, A summing amplifier that has a video demodulation circuit that demodulates a video signal from the output signal of the auto gain control circuit and adds and amplifies two playback signals output from the magnetic pickup extracts the DC component of the output signal of the summing amplifier. and (1) of the output signal of this low-pass filter.
±α) times the DC voltage VT; a low-pass filter that limits the band of the output signal of the summing amplifier; A voltage comparator to be compared, a pulse width discrimination circuit that discriminates the pulse width of the output signal of this voltage comparator and generates two types of defect detection flag signals, large and small, and a defect detection flag output from this pulse width discrimination circuit. The video signal demodulation circuit includes a dropout correction circuit that corrects dropout of the video signal output from the video signal demodulation circuit by holding the previous value.

Effect of the Invention With the above-described configuration, the present invention does not detect a dropout from a differential signal of two reproduced signals that are output from a magneto-optical pickup and have a phase difference of 180 degrees, that is, a reproduced RF signal, but detects a dropout from an added signal, that is, from a reproduced RF signal. Since dropouts are detected by detecting pulsed noise from a signal reflecting the groove reflectance of the magneto-optical disk, dropouts distributed in the band around the FM carrier frequency can also be properly detected. be.

Embodiment Hereinafter, an optical recording/reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of an optical recording/reproducing apparatus according to an embodiment of the present invention.

In FIG. 1, 11 is a bin photodiode, 12 is a differential amplifier, 13 is a band pass filter, 14 is an auto gain control circuit, 15 is a video signal demodulation circuit,
16 is a dropout correction circuit, 17 is a summing amplifier, 1
9 is a voltage comparator, 20 is a pulse width discrimination circuit, 18.21
2 is a low-pass filter, and 22 is a reference voltage generation circuit.

Regarding the optical recording and reproducing device configured as above,
The operation will be explained below using FIGS. 1 and 2.

First, in FIG. 1, the signal output from the bin photodiode 11 of the magneto-optical pickup is sent to a differential amplifier.
2 to obtain a reproduced RF signal. This reproduced RF signal is filtered by a bandpass filter 13.
The frequency band is limited to about 10 KHz to 10 MHz, and after the width is kept constant by the auto gain control circuit 14, it is demodulated by the video signal demodulation circuit 15 to obtain a video signal.

Typically, the error rate of optical disks, including magneto-optical disks, is 10, so dropouts exist in this video signal. This dropout is corrected by the dropout correction circuit 16 using means such as holding the previous value, but in this embodiment, in order to detect this dropout, the output from the signal detection bin diode 11 of the magneto-optical pickup is By adding the signals reflected by the summing amplifier circuit 17, a signal reflecting the groove reflectance of the magneto-optical disk is obtained, and pulse-like noise occurring on this signal is detected, and groove disturbances and substrate material are detected. Detects dropouts caused by internal foreign objects, etc. That is, the output of the summing amplifier 17 is band-limited to DC to IOM) (x) by the low-pass filter 18, and the voltage comparator 19 detects pulse-like noise, that is, a steep change in reflectance, and drops out. The reference voltage value for determining pulse-like noise in the voltage comparator 19 is determined by extracting only the DC component of the groove reflectance signal using the low-pass filter 21, and then extracting the DC component (1±α) times the DC component in the reference voltage generation circuit. It is set by generating a DC voltage value.The judgment value of pulse-like noise in the groove reflectance signal is set at α=0.2~
By setting it to about 0.25, it is possible to best deal with dropouts on the reproduced RF signal.

On the other hand, the defect detection flag signal output from the voltage comparator 19 is classified by the pulse width discrimination circuit 20 into a small defect of 1 μs or less and a large defect of 1 μs or more, and a dropout correction circuit 16. In the dropout correction circuit 16, dropouts on the video signal are corrected for small defects by holding the previous value, and for large defects by means such as IH interpolation.

Effects of the Invention As described above, according to the present invention, the groove reflectance of a magneto-optical disk is monitored, dropouts are detected as pulse-like noise on the groove reflectance signal, and the judgment value of this pulse-like noise is also determined. is detected using a voltage comparator as (1±α) times the average value of the groove reflectance (α = 0.2 to 0.25), so small dropouts distributed around the FM carrier frequency can be detected. It is also possible to properly detect dropout and enable good dropout correction.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an optical recording/reproducing apparatus according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of its operation, Fig. 3 is a block diagram of a conventional optical recording/reproducing apparatus, and Fig. 4 is its operation diagram. It is an operation explanatory diagram. 1.11...Pin photodiode for signal detection, 2,12...Differential amplifier, 3,13...
... Band pass filter, 4.14 ... Auto gain control circuit, 5, 15 ... Video signal demodulation circuit, 6, 16 ... Dropout correction circuit, 7. ...Envelope detection circuit, 8,1
9... Voltage comparator, 17... Summing amplifier, 20... Pulse width discrimination circuit, 18.21.
...Low pass filter, 22...Reference voltage generation circuit.

Claims (2)

[Claims] (1) A magneto-optical pickup equipped with a differential optical system that records, reproduces, and erases signals using the magneto-optic effect;
a differential amplifier path that differentially amplifies two reproduction signals; a bandpass filter that limits the band of the output signal of the differential amplifier; and an auto gain control circuit that keeps the amplitude of the output signal of the bandpass filter constant; The summing amplifier includes a video demodulation circuit that demodulates a video signal from the output signal of the auto gain control circuit, and adds and amplifies two reproduction signals output from the magneto-optical pickup. a first low-pass filter for extracting the component; a reference voltage generation circuit for generating a DC voltage (1±α) times the output signal of the first low-pass filter; and a first low-pass filter for band-limiting the output signal of the summing amplifier. a voltage comparator that compares the output signal of the second low-pass filter with the reference voltage value output from the reference voltage generation circuit; A pulse width discrimination circuit that generates two types of defect detection flag signals, and a defect detection flag signal output from the pulse width discrimination circuit,
An optical recording and reproducing apparatus comprising: a dropout correction circuit that corrects dropout of the video signal output from the video signal demodulation circuit by holding a previous value. (2) DC voltage value V_ generated by the reference voltage generation circuit
Claim 1, wherein T is V_T=(1±α)·V_D_C [α=0.2 to 0.25], where V_D_C is the DC component of the output signal of the summing amplifier. The optical recording/reproducing device described in .