JPS58119287A - Generating circuit for pilot burst eliminating instruction signal - Google Patents

Abstract

PURPOSE:To eliminate the pilot burst in a reproducing signal, by selectively picking up a frequency part corresponding to a syncyronizing tip level in a reproducing RF signal of a color video of the PAL system and generating a pilot burst eliminating command signal. CONSTITUTION:A selecting switch 1 selects either the reproduced RF signal or that 1H before, by dropout detection and the signal is applied to an FM demodulator 2 and a pilot burst eliminating instruction signal generating circuit 3. The center frequency of a narrow band filter 4 of the circuit 3 is equal to the frequency corresponding to the synchronizing tip level of a reproducing video signal obtained by FM-demodulating the reproduced RF signal, an output B has larger amplitude of the frequency part corresponding to the syncyronizing tip level, and when the level is detected as a prescribed value or over at a signal level detection circuit 5, and a command signal C eliminating a pilot burst signal (a) included in the synchronizing signal in the reproduced video signal A being an output of the FM demodulator 2 is applied to an eliminating circuit 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for generating a pilot burst removal command signal to remove a pilot burst inserted into a synchronization signal in an M raw signal of PALPAL video information.

In a PAL color video signal, a color burst signal is inserted every 1--2 lines with a 90° phase difference. For this reason, in a color video information reproducing device, it is difficult to control the movement of a reading pickup in the tangential direction of a recording disk's track while correcting the time axis by comparing the phase of the color burst signal with a separately provided reference signal. ing. Therefore, during recording, a so-called pilot burst signal having a frequency that is an integral multiple of the horizontal synchronization signal is inserted into the synchronization signal, and during playback, this pilot burst signal is separated and extracted, and the phase is compared with the reference signal. The signal is used to accurately correct the time axis.

Even after this pilot burst signal is separated and extracted for time axis correction, if it exists in the reproduced video signal, problems such as synchronization disturbance may occur in video playback devices, etc. Therefore, a removal circuit that removes the pilot burst signal is provided in the color video information reproducing device. In a conventional color video information reproducing apparatus, a pulse obtained by comparing a reproduced video signal with a predetermined slice level in a synchronization separation circuit is used as a pilot burst removal command signal supplied to this removal circuit. Such a conventional color video information reproducing apparatus has a problem in that the pilot burst signal cannot be completely removed due to the time delay of the signal in the synchronization separation circuit.

In order to solve this problem, if the circuit constants of the synchronization separation circuit are set so as to reduce the time delay of the signal in the synchronization separation circuit, the RF multiplied signal is dropped due to dropout, and the level of the video signal portion of the reproduced video signal, for example, becomes higher than the synchronization signal. When the level drops significantly below the slice level of the separation circuit, the lowered level portion is separated and extracted in the same way as the synchronization signal, making it easy to cause a malfunction in which a pilot burst removal command signal is erroneously generated.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pilot burst removal command signal generation circuit which generates a pilot burst removal command signal so as to completely remove the pilot burst signal and which is less prone to malfunction due to dropout.

A pilot burst removal command signal generation circuit according to the present invention includes a narrow band filter that selectively extracts a frequency portion corresponding to a sync tip level in a reproduced RF signal consisting of an FM signal, and the signal level of the output of this filter is equal to or higher than a predetermined level. It is configured to generate a pilot burst removal command signal when the

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, a reproduced RF signal consisting of an FM signal and a reproduced RF signal before IH (one horizontal period) of this reproduced RF signal
A signal is supplied to each of the two input terminals of the signal selection switch 1. The selection switch 1 selects one of the reproduced RF signal and the pre-IH reproduced RF signal supplied in response to a dropout detection signal outputted from a dropout detection means (not shown) for detecting a dropout of the reproduced RF signal. Selectively output one or the other. The output of the selection switch 1 is supplied to a post-rain adjuster 2 and a pilot burst removal command signal generation circuit 3 according to the present invention. In the pilot burst removal command signal generation circuit 3, the output of the selection switch l is supplied to the narrow band filter 4. The center frequency of the narrow band filter 4 is approximately equal to the frequency corresponding to the 7 step level in the reproduced video signal obtained by FM demodulating the reproduced RF signal. The output of this narrow band filter 4 is supplied to a signal level detection circuit 5. The signal level detection circuit 5 includes, for example, envelope detection means for detecting the envelope of the output of the narrow band filter 4 and outputting a signal having almost the same waveform as the envelope, and the output of the envelope detection means as a predetermined reference voltage. In addition to a comparator for comparison, the comparator outputs multiple pulses as a pilot burst removal command signal in accordance with the level of the output of the envelope detection means. The pilot burst removal command signal output from the signal level detection circuit 5 is supplied to the control input terminal of the removal circuit 6 as an output of the removal command signal generation circuit 3. On the other hand, the output of the selection switch l supplied to the FM demodulator 2 is FM demodulated and becomes a reproduced video signal.
is supplied to the input terminal of The removal circuit 6 includes, for example, as shown in FIG. 3, a series resonant circuit 7 having one end connected to the input terminal IN and having a resonant frequency almost the same as the natural frequency of the pilot burst signal, and the other end of the series resonant circuit 7. and a switching element 8 connected between the control input terminal and the ground and having a control input terminal supplied with a pilot burst removal command signal, and the switching element 8 responds to the pilot burst signal by turning on and off in response to the pilot burst removal command signal. After frequency components are removed, the reproduced video signal is output to the output terminal otyr.

In the above configuration, a pilot burst signal α is present in the synchronization signal of the reproduced video signal outputted from the FM demodulator 2 as shown in FIG. On the other hand, in the narrow band filter 4 to which the output of the selection switch l is supplied, only the portion of the reproduced video signal excluding the frequency portion corresponding to the sync tip level is attenuated, so that the amplitude of the frequency portion corresponding to the sync tip level is compared. As a result, a frequency portion corresponding to the sync tip level is extracted as shown in FIG. 2(b). Therefore, when the instantaneous frequency of the reproduced RF signal consisting of the FM signal becomes approximately equal to the frequency corresponding to the sync tip level of the reproduced video signal, the signal level of the output of the narrow band filter 4 will not exceed the predetermined level. A pilot burst removal command signal consisting of positive pulses as shown in FIG. 2 (0) is sent to the signal level detection circuit 5.
It will be outputted. By supplying this pilot burst removal command signal to the removal circuit 6, the pilot burst signal is removed.

In the above operation, the pilot burst removal command signal is obtained by selectively extracting the frequency portion of the reproduced RF signal that corresponds to the sync chip level of the reproduced video signal, so the reproduced RF signal is FM demodulated. The time delay of the pilot burst removal command signal with respect to the synchronization signal in the obtained reproduced video signal is eliminated, and the pilot burst signal can be almost completely removed. Furthermore, even when a dropout occurs in which the level of the video signal portion of the reproduced video signal is greatly reduced, the narrowband filter 4 prevents the pilot burst removal command from being issued because there is no frequency portion corresponding to the video signal portion. This will prevent the occurrence of malfunctions in which signals are generated.

As described in detail above, the pilot burst removal command signal generation circuit according to the present invention is configured to be able to almost completely remove the pilot burst signal and to prevent malfunctions such as erroneously generating a pilot burst removal command signal. The present invention is suitable for use in video tape recorders, video disc players, etc. that record or reproduce color video signals of the same format.

[Brief explanation of the drawing]

1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a waveform diagram showing the circuit operation of FIG. 1, and FIG. 3 is a circuit diagram showing a specific circuit example of the removal circuit 6. . Explanation of symbols for main parts 4 Narrowband filter 5 Signal level detection circuit Applicant Universal Pioneer Co., Ltd. Agent
Patent Attorney Hikomitsu Fujimura Moto/Illustrated Book-II121

Claims (1)

[Claims] A pilot burst removal command that generates a pilot burst removal command signal to cause a removal circuit to remove a pilot burst signal for time axis correction inserted into a synchronization signal in a reproduction signal of PAL color video information to perform a removal operation. The signal generation circuit includes a narrowband filter that selectively extracts a frequency portion corresponding to a sync tip level in a reproduced RF signal consisting of an FM signal, and a signal level of an output of the narrowband filter is equal to or higher than a predetermined level. and signal level detection means for generating the pilot burst removal command signal when the pilot burst removal command signal is detected.