JPS6261Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a read pulse generating circuit with stable operation.

When recording an audio signal as a PCM signal on a disc-shaped recording medium, the PCM signal is usually converted into a video signal and recorded, and the readout of the reproduced PCM signal is periodic and involves the temporal fluctuation components of the reproduced PCM signal. The oscillation output of an oscillation circuit whose synchronous input is a regenerated horizontal period signal having . However, it has been confirmed that such an oscillation circuit also causes synchronization disturbances due to dropout noise mixed into the horizontal synchronization signal, leading to reading errors in the normal horizontal synchronization section following the dropout occurrence area. .

Therefore, in view of the above-mentioned points, the present invention aims to propose a read pulse generation circuit that eliminates the noise component from the horizontal synchronization separated output and is free from malfunctions due to noise.

The present invention will be described below with reference to an illustrative embodiment. The feature of this embodiment is that it focuses on the fact that dropout noise mixed into the horizontal synchronization signal often reaches a level lower than the synchronization tip of the horizontal synchronization signal, and prevents the derivation of such noise. In addition, only the output corresponding to the width of the horizontal synchronization signal is determined and derived, and is used as the synchronization input to the synchronization oscillation circuit for reading the PCM signal. In other words, in this embodiment, the reproduced PCM signal (FIG. 2a) derived by FM demodulating the FMPCM signal reproduced from the video disc is
is input to a first voltage comparator circuit 1 whose set level is slightly higher than the horizontal synchronization tip, and a dropout detection circuit (second voltage comparator circuit) 2 whose set level is slightly lower than the synchronization tip. By applying the output (FIG. 2b) as a control input to the first voltage comparator circuit 1, a dropout output is prevented from being derived from the first voltage comparator circuit 1. However, the first
Although the comparison output (FIG. 2c) derived from the voltage comparison circuit 1 prevents the generation of dropout output, it leaves pulse-like noise in the blocked portion. Therefore, in this embodiment, the comparison output c is further inputted to a pulse width discrimination circuit to prevent the derivation of noise pulses other than the pulse width of the horizontal synchronization pulse, and the discrimination output d is used as a synchronization input to a synchronous oscillation circuit for generating read pulses. 4 to control the phase of the PCM signal reading pulse.

As is clear from FIG. 2, the discrimination output d includes a missing portion of the horizontal synchronizing signal due to dropout, but even if one or two synchronizing inputs to the synchronous oscillation circuit 4 are missing, the phase of the read pulse will fluctuate. It was also confirmed that inputting a pseudo-horizontal synchronization signal whose phase is slightly out of phase to the synchronization oscillation circuit 4 may greatly disturb the phase of the read pulse.

Therefore, according to the present invention described above, it is possible to generate a read pulse with stable operation despite the occurrence of dropout, and the effect is great.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an implementation circuit of the present invention;
The figures each show the same waveform explanatory diagram. Explanation of main figure numbers, 1... Voltage comparator circuit, 2...
Dropout detection circuit, 3... Pulse width discrimination circuit, 4... Synchronous oscillation circuit.

Claims (1)

[Scope of utility model registration request] In a PCM playback circuit that plays back a PCM signal converted into a video signal from a recording medium and reads the PCM signal using a read pulse synchronized with a negative playback synchronization signal, the level of the playback PCM signal is lower than the synchronization tip of the playback synchronization signal. a dropout detection circuit that detects dropout noise, and a voltage comparison circuit that detects low-level signals, including the playback synchronization signal, from the playback PCM signal and prevents dropout noise from being generated by the dropout detection output. , a pulse width discrimination circuit that derives only an output that matches the pulse width of the synchronization signal from the voltage comparison output, and a synchronous oscillation circuit that derives a PCM signal read pulse in synchronization with the discrimination output. generation circuit.