JPS6398873A - Recorded information reproducing device - Google Patents

Abstract

PURPOSE:To suppress the generation of a line noise without losing the secondary distortion correcting effect by connecting a synchronizing separation circuit to the output side of an FM demodulator and providing a switch switching a trap circuit provided at the pre-stage of a limiter circuit by an output of the synchronizing separation circuit. CONSTITUTION:An output of a detector 3 extracted via a reproducing stylus 2 is subject to distortion correction by the secondary distortion correction circuit 4, the secondary distortion component for a tracking signal and a video signal is eliminated by an equalizer 5, waveform-shaped by a limiter circuit 6 and demodulated into a video signal via an FM demodulator 7 and an LPF8. Since the second harmonic component of the carrier is high in the demodulated signal, only the video signal is extracted by an LPF9 and the result is inputted to a synchronizing separator circuit 10. In switching a switch 12 during a synchronizing signal period by using the separated synchronizing signal, the input signal to the limiter circuit 6 subject to attenuation of a level near the synchronizing signal and the carrier leak level in the demodulated signal and its fluctuation component are eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an information recording/reproducing device having a feature of reducing line noise in a capacitive (VHD) type video disc player. Video discs have spread rapidly in the consumer market, and are establishing a foundation as a large home appliance product.

Now, a VHD type video disc player generally includes a secondary distortion correction circuit in order to remove distortion components generated in the medium (disc) and the detector.

The configuration of a conventional video signal processing circuit will be described below with reference to FIG.

In Fig. 6, 1 is a disk, 2 is a playback needle, 3 is a detector, 4 is a secondary distortion correction circuit, 5 is an equalizer, 6 is a limiter, FM demodulator, 8 is an LPF, 13 is a video signal It is an output terminal.

Further, FIG. 2 shows a VHD signal format, and FIG. 4 shows a specific circuit example of the secondary distortion correction circuit 4. Furthermore, FIG. 3 shows a spectrum diagram of the synchronization signal section. Third
In the figure, fT is the tracking signal inserted in the blanking section, fa□ is the audio lower sideband, fc is the video (synchronization) carrier wave, fau is the audio upper sideband, 2 f3
is the second-order distortion component of the carrier wave.

Now, in FIG. 5, from the rotationally driven disk 1, the playback needle 2. The disk signal taken out through the detector 3 theoretically has a spectrum as shown in Figure 2, but
In VHD video disk players, various cross-modulation distortion components as shown in Figure 3 are actually generated due to distortion caused by the capacitance detection method and distortion caused by the dielectric constant of the playback needle (diamond with a thin electrode). have

Among these, the 2fB-fT acid component is a disturbing component that has a large amount in terms of image quality, and in order to correct this disturbing component,
A second-order distortion correction circuit 4 is inserted.

This actual circuit example has a circuit configuration as shown in FIG. 4A,
Distortion correction is performed by performing a one-sided clipping operation using the nonlinear element 15 shown in FIG.

That is, in video demodulation of a VHD player, as shown in FIG. 5, after distortion is corrected by a secondary distortion correction circuit 4 based on the output of a detector 3, the tracking signal and secondary distortion components of the video are removed by an equalizer. The frequency characteristics of equalizer 6 are
After the waveform is shaped by the limiter 6, the video signal is demodulated through the FM demodulator 17 and LPFs.

Problems to be Solved by the Invention However, in such a conventional configuration, the disk 1
This has the problem of generating and increasing line noise due to gap fluctuations between the reproducing needle 2 and the reproducing needle 2.

That is, the existence of multiple carriers, ie, carrier waves and tracking signals, in the synchronization signal section generates spurious components as shown in FIG. 3 due to nonlinear elements. moreover,
Due to the above gap fluctuation, 2fs and 2fs in Fig. 3
The ±fT component fluctuates, and by passing this signal through a second-order distortion correction circuit, pseudo duty cycle modulation is achieved.

This increases the 2f3 component. That is, in the demodulated signal, carrier leakage increases only during the synchronization period. This is done by the sync tip clamp circuit.
It becomes line noise.

In view of the above-mentioned problems, the present invention provides a recorded information reproducing apparatus that suppresses the generation of line noise without impairing the secondary distortion correction effect.

Means for Solving the Problems In order to achieve this object, the recorded information reproducing apparatus of the present invention includes a synchronization separation circuit connected to the output side of the FM demodulator, and a stage before the limiter that includes: 2. It is comprised of a trap circuit that attenuates f3 and 2fs±fT components, and a switch that opens and closes the trap circuit using the output of the synchronous separation circuit.

Effect: With this configuration, the second-order distortion components (2f3 and Qfs±fT) in the synchronization section are attenuated, and generation of line noise is suppressed during FM demodulation.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a recorded information reproducing apparatus in an embodiment of the present invention. In FIG. 1, 1 is a disk, 2 is a playback forceps, 3 is a detector, 4 is a secondary distortion correction circuit, 5 is an equalizer, 6 is a limiter circuit, a TuvMa adjustment device, 8 is an LPF (low-pass filter), and 13 is an image The signal output terminal has the same structure as the conventional example shown in FIG. 5.

Furthermore, 9 is the output f! of the FM demodulator 7! 10 is a synchronous separation circuit connected to the output terminal of LPF 9, 11 is a trap circuit inserted before the limiter circuit 6, and 12 is inserted between trap circuit 11 and the reference potential. It's a switch.

The operation of the recorded information reproducing apparatus configured as described above will be explained below.

First, the signal passed through the playback needle 2 from the disk 1 and extracted by the detector 3 is passed through the secondary distortion correction circuit 4 to attenuate the cross-modulation component (2fs-fT in Fig. 3), and then converted into a tracking signal. It is removed by the equalizer 5 (the frequency characteristics of the equalizer 6 at that time are shown in FIG. 6a). Further, a limiter circuit performs waveform shaping, and an FM demodulator 7 demodulates the video signal. Since this demodulated signal has a high secondary component of the carrier wave, only the video signal is extracted by the LPF9.
The signal is input to the same 1υ1 separation circuit 10. This separated synchronization signal causes the switch 12 to shut off only during the synchronization signal period, so that the level of the input signal to the limiter circuit 6 near the jυJ signal is attenuated through the trap 11. The characteristics of the equalizer at this time are shown in FIG. In other words, only the synchronization signal section is 2fs in FIG.
By attenuating the 2fs:l:fT acid component, the carrier leak level in the demodulated signal and its fluctuation component are removed, making it possible to suppress the generation of line noise. Furthermore, by limiting this attenuation section to the synchronization signal section, it is possible to prevent the occurrence of an inversion phenomenon due to a reduction in the upper sideband in the video section.

In this embodiment, the second-order distortion correction circuit 4
Although the effect is obtained by eliminating the occurrence of f3±fT, fs±fT may increase depending on other specific circuit configurations of the secondary distortion correction circuit 4 mentioned in this embodiment.

At this time, the trap path 11 may be connected to the front stage of the secondary distortion correction circuit 4.

Effects of the Invention As described above, according to the present invention, by attenuating carrier leak only in the synchronization signal section, generation of line noise can be suppressed without adversely affecting beat removal and inversion phenomenon caused by the secondary distortion correction circuit. is possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a recorded information reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a format diagram of a VHD signal, FIG. 3 is an actual detected spectrum diagram in a synchronization signal section, and FIGS. 4A and B are diagrams. FIG. 5 is a block diagram of a conventional example, and FIG. 6 is an equalizer characteristic diagram of the conventional example and the present invention. 1...disc, 2...playback needle, 3...mountain...detector, 4...secondary distortion correction circuit, 5...
...Equalizer, 6...Limiter [[1st path,
7...FM demodulator, 8...LPF, 9
...LPF, 10...Synchronization separation circuit,
11...L-wrap circuit, 12...Switch. Name of agent: Patent attorney Toshio Nakao and 1 other person f~
--Disc? -・Ai multi-j゛gSl Figure 11. −
Gaku 13 Episode f2・-12 Inote Figure 2 Figure 3

Claims (2)

[Claims] (1) The video information is transmitted from a recording medium having a first signal in which the video information signal is low-carrier FM modulated, and a second signal intermittently inserted into a low frequency outside the band of the first signal. A device for demodulating a signal, comprising a detection means for detecting the first and second signals from the recording medium, a correction circuit for correcting distortion in the output of the detection means, and a waveform shaping of the output of the correction circuit. and means for attenuating a cross modulation component between a second harmonic component of the first signal and the first signal in the insertion section of the second signal and inputting it to the waveform shaping circuit. A recorded information reproducing device characterized by: (2) The recording according to claim 1, wherein the section in which the second harmonic of the first signal and the cross-modulation component of the second signal are attenuated is a synchronization signal section of the video signal. Information reproducing device.