JPH0720231B2 - Sync signal detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for reading FM-modulated information from a moving recording medium, and more particularly to a synchronizing signal detecting apparatus for the same.

2. Description of the Related Art An optical video disc player will be described as an example.

FIG. 3 is a block diagram of an optical video disc player for reading a video signal optically FM-modulated from a rotating disc. 1 is a read head, 2 is a high-pass filter, and 3 is a high-pass filter.
Is FM demodulation means, 4 is synchronization detection means, 5 is phase comparison means,
Reference numeral 6 is a recording medium moving means, and 7 is a recording medium. The reading head 1 optically reads information from the recording medium 7 and outputs an RF signal. In the case of an optical video disc player, since the video signal is recorded by direct FM modulation, this RF signal is FM modulation of the video signal.
The RF signal passes through a simple high-pass filter 2 with a low cutoff frequency that drops noise components and audio FM components due to undulations of the disc, and then demodulates the video signal with a wide band FM demodulation means 6. And output. Here, as flat a characteristic as possible is required in the FM band. This video signal further passes through the sync detecting means 4 to become a sync signal, which is compared with the reference signal by the next phase comparing means 5 and serves as a control signal for the recording medium moving means 6 which rotates the recording medium 7 and is always reproduced. The synchronization signals are controlled so that the intervals between them are constant. (For example, OplusE, No.59, pp73 to 78) Problems to be solved by the invention When the RF signal has a recess as shown in Fig. 4 (a) due to a dropout of the recording medium, the amplitude limit of the FM demodulator is limited. Since the pulse of the output of the vessel is missing as shown in FIG. 4 (b),
A pulse as shown in Fig. 4 (c) is generated in the output after FM demodulation. Normally, not only in the optical video disc player but also in the video tape recorder, the sync tip is modulated so as to have a frequency lower than the white level. Therefore, such a pulse is generated on the same side as the sync signal, and the optical video disc player The spindle motor control and the time axis control circuit that is controlled based on the synchronization signal have been a disturbance.

Means for solving the problem First high-pass filter for inputting RF signal and first FM for detecting output of first high-pass filter to obtain reproduced signal
Second high-pass filter for inputting demodulation means and RF signal, second FM demodulation means for detecting output of second high-pass filter, and synchronization detection for extracting synchronization signal from output of second FM demodulation means Means for setting the cutoff frequency of the second high pass filter higher than the cutoff frequency of the first high pass filter.

Action Even if the RF signal has a dent due to the dropout of the recording medium, by setting the cutoff frequency of the second high-pass filter high, it is possible to prevent the loss of the O-cross signal necessary for FM demodulation. The synchronization signal of becomes stable. Therefore, stabilization of the operation of the control circuit using this synchronization signal,
After all, it helps stabilize the entire system.

Example A sync signal detecting device according to an example of the present invention will be described below.
This will be described in detail with reference to the drawings.

Here again, an optical video disc player will be described as an example.

FIG. 1 is a block diagram showing an embodiment of the present invention. A reading head 1 optically reads information from a recording medium 7 and outputs an RF signal. One of the RF signals is a wide band through a simple first high-pass filter 2a with a low cut-off frequency that drops a noise component or a voice FM component that is reduced due to the waviness of the disc in order to output a reproduced video signal. It is demodulated by the first FM demodulation means 3a set to. The first high-pass filter 2a and the first FM demodulation means 3a are designed to pass the entire FM pass band as flat as possible without deteriorating the quality of the reproduced image. The RF signal is further demodulated by another second high-pass filter 2b and second FM demodulation means 3b, and then the synchronization detection means 4 separates the synchronization signal. By setting the cut-off frequency of the second high-pass filter 2b higher than the cut-off frequency of the first high-pass filter, the depression caused by the fine dropout of the RF signal shown in FIG. After passing through the high-pass filter, O-cross occurs as shown in FIG. 2 (b). Therefore, the output of the amplitude limiter of the second FM demodulation means does not lack a pulse as shown in FIG. 4 (c), and the output (d) of the second FM demodulation means may be the same as the synchronization signal. Generation of pulse can be prevented. The synchronization signal thus stably extracted is compared with the reference signal by the phase comparison means 5 and becomes a control signal of the recording medium moving means 6 for rotating the recording medium.
It is controlled so that the intervals of the reproduced sync signals are always constant. Also, by limiting the FM band with the second high-pass filter here, the demodulation output of the second FM demodulator also has a slightly distorted waveform, but the timing error of the synchronization signal due to the distorted waveform is small. If necessary, it can be easily removed by another time axis control means using a burst signal, which is not a big drawback. The synchronization signal obtained by the present invention may be used as a time axis control using a CCD (charge storage device) or an electronic variable delay line, or as a control signal for general systems, and an optical video disc player is taken as an example. However, it does not matter if it is magnetically read out, such as a video tape recorder, or it is read out by another method.
The present invention can be applied to any medium that can read a recorded medium.

Needless to say, the input of the second high pass filter is the same after the first high pass filter.

EFFECTS OF THE INVENTION Even if a dent occurs in the RF signal due to a dropout of the recording medium or the like, stable synchronization detection can be performed without the occurrence of a pulse that causes disturbance after FM demodulation. This helps stabilize various control circuits using the reproduction synchronization signal, and eventually the entire system, and has a great effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 (a), (b), (c), and (d) are waveform diagrams of FIG. 1, and FIG. 3 is a conventional synchronization detecting device. FIG. 4 is a block diagram of the main part of an optical video disc player including
(B), (c) is a waveform diagram of FIG. 2a ... first high-pass filter, 2b ... first FM demodulator, 3a ... second high-pass filter, 3b ... second FM demodulator.

Claims (1)

[Claims] 1. A recording medium on which an FM-modulated video signal is written, a reading head for reading information from the recording medium and outputting an RF signal, and a first high-pass filter for inputting the RF signal. And a first FM demodulation means for detecting the output of the first high-pass filter to obtain a reproduced signal,
A second high-pass filter that receives the RF signal and has a cut-off frequency higher than a cut-off frequency of the first high-pass filter and a second high-pass filter that detects outputs of the second high-pass filter.
A synchronization signal detecting device comprising FM demodulation means and synchronization detection means for extracting a synchronization signal from the output of the second FM demodulation means.