JPH0834604B2 - Optical disc player - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical disk player, and more particularly, to an optical disk player.
It relates to the structure of an RF band filter.

[Prior Art] FIG. 5 shows an example of a video signal reproducing circuit of a conventional optical disc player.

Reference numeral 1 shown in the figure is an optical pickup, which extracts an RF signal from the reflected light from the optical disk.

After the RF signal is amplified by the RF amplifier 2, the band filter 5
The video FM signal is taken out through, and the video FM signal is detected by the FM detector 6 to obtain the video signal.

The video signal is time-axis corrected by the CCD variable delay line 8 and becomes a reproduced video signal.

The time base correction is performed by a TBC (time base collector) circuit 21 shown in the figure.

That is, the horizontal synchronizing signal separated by the horizontal synchronizing signal separation circuit 9 is phase-compared with the reference signal oscillated by the crystal oscillator 15 and divided by the frequency divider 14 by the phase comparator 10, and the error signal thereof is low-pass filter 16 After passing through, it is added by the adder 18.

Further, the color burst signal extracted from the burst gate 11 whose transit time is controlled by the color burst gate signal obtained from the horizontal synchronizing signal separation circuit 9 is amplified by the burst signal amplifier 12 and then oscillated by the crystal oscillator 15 to be divided. Circulator
The reference signal divided by 14 is phase-compared with the phase comparator 13, and the error signal passes through the low-pass filter 17,
It is added by the adder 18.

The phase error signal obtained by adding in the adder 18 is amplified by the error signal amplifier 19 and controls the oscillation frequency of the voltage controlled oscillator 20.

The delay time of the CCD variable delay line 8 is controlled by the oscillation frequency of the voltage controlled oscillator 20 to absorb the jitter.

[Problems to be Solved by the Invention] The video FM signal recorded on the optical disk has a band (9 MHz) of about 3 MHz to 14 MHz as shown in FIG. 2, and the band filter 5 is adapted to the band. In this way, since the bandwidth of the bandwidth filter 5 is wide, a large S / N ratio of the horizontal synchronizing signal and the reproduced color burst signal cannot be obtained, so that the phase comparison operation of the TBC circuit 21 is not accurately performed and the jitter is absorbed. There was a problem that it was not enough. The fifth
The loop gain of the TBC servo system composed of the CCD variable delay line 8, the horizontal sync signal separation circuit 9, the phase comparator 10, the low-pass filter 16, the adder 18, the error signal amplifier 19 and the voltage controlled oscillator 20 in the figure is the CCD. Compared to the loop gain of the burst signal system composed of variable delay line 8, burst gate 11, burst signal amplifier 12, phase comparator 13, low-pass filter 17, adder 18, error signal amplifier 19 and voltage controlled oscillator 20. It is low, and in steady state, the amount of jitter absorption of TBC is determined by the control performance of the burst signal system.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical disk player that reproduces a color burst signal having a good S / N ratio and has little jitter in a reproduced video signal.

[Means for Solving the Problems] The optical disc player of the present invention is used as a band filter for extracting a video FM signal from an RF signal amplified by an RF amplifier in an optical disc player for reproducing an optical disc on which a video signal is recorded by frequency modulation. 3 according to the spectrum of the signal frequency-modulated by the band filter and color burst signal that match the frequency band of the video FM signal
A band burst filter having two peaks is provided by a switch to be used, and a color burst gate signal generated by adjusting the ON period by the horizontal sync signal extracted by the horizontal sync signal separation circuit allows only the color burst period. The switch is changed over to use the band filter having the three peaks.

[Operation] As shown in Fig. 3, when the modulation index of the FM signal spectrum of the color burst signal is small like that of an optical disc,
It can be regarded as only 3 waves of 4.52MHz, 8.1MHz and 11.68MHz. Therefore, in the color burst period, the band filter that passes the RF signal is made to pass only the above three waves. For example, if the bandwidth for each wave is 0.5 MHz, the total bandwidth becomes 0.5 MHz × 3 = 1.5 MHz, It is 1/6 of the bandwidth 9MH of the normal band filter, and the reproduction S / N ratio of the color burst signal after FM demodulation is improved by 7 to 8dB compared to when the normal band filter is used.

In this way, the noise component of the reproduced color burst signal is removed. The TBC jitter absorption increases in the steady state.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a video signal reproducing circuit of an optical disk player which is an embodiment of the present invention.

In this embodiment, the band filter 5 shown in FIG.
A band filter 4 is provided in parallel with the same band filter 5 as above via switches 3 and 3. The switches 3 and 3 are switched by the color burst gate signal generated by the burst gate signal generation circuit 7 and are connected to the band filter 4 side only during the color burst period.

The burst gate signal generation circuit 7 is a conventionally well-known circuit for generating a gate signal used when extracting a burst signal from a video signal. Since the burst signal is generated with a delay of a certain time from the horizontal synchronization pulse, the horizontal synchronization signal is generated. It is composed of a signal separation circuit and a delay circuit.

As shown in FIG. 4, the band filter 4 has three LC series connection circuits connected in parallel, and the band center frequency of each LC series circuit is 4.52, which is the center frequency of the spectrum of the color burst signal shown in FIG. It matches with MHz, 8.1MHz and 11.68MHz.

 The configuration of the other parts is similar to that shown in FIG.

With the above configuration, the noise component of the reproduced color burst signal is removed during the color burst period, and the TBC jitter absorption amount in the steady state increases.

[Effects of the Invention] As described above, according to the optical disk player of the present invention, since the TBC jitter absorption amount in the steady state is large, it is possible to obtain the effect that the occurrence of color unevenness in the video signal is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a video signal reproducing circuit of an optical disc player which is an embodiment of the present invention, and FIG. 2 is a spectrum distribution diagram of a video FM signal recorded on an optical disc,
FIG. 3 is a spectrum distribution diagram of a color burst signal recorded on an optical disc, FIG. 4 is a circuit diagram of the band filter 4 in the embodiment, and FIG. 5 is a block diagram showing an example of a video signal reproducing circuit of a conventional optical disc player. It is a figure. 1 ... Optical pickup, 2 ... RF amplifier, 3 ... Switch, 4 ... Band filter, 5 ... Band filter, 6 ...
FM detector, 7 ... Burst gate signal generation circuit, 8 ...
CCD variable delay line, 9 ... Horizontal sync signal separation circuit, 10 ...
Phase comparator, 11 ... burst gate, 12 ... burst signal amplifier, 13 ... phase comparator, 14 ... frequency divider, 15 ... crystal oscillator, 16, 17 ... low-pass filter, 18 ... adder , 19 ... Error signal amplifier, 20 ... Voltage controlled oscillator,
21 ... TBC circuit.

Claims (1)

[Claims] 1. A band filter matched with a frequency band of a video FM signal as a band filter for extracting a video FM signal from an RF signal amplified by an RF amplifier in an optical disk player for reproducing an optical disk having a video signal recorded by frequency modulation. And a band filter having three peaks matching the spectrum of the signal frequency-modulated by the color burst signal are provided by a switch to be used, and an ON period is set by the horizontal synchronization signal extracted by the horizontal synchronization signal separation circuit. An optical disc player configured to use the bandpass filter having the three peaks by switching the switch only during a color burst period by a color burst gate signal generated by adjusting.