JPH02183690A - Burst gate control circuit - Google Patents

Abstract

PURPOSE:To eliminate a hue change at an upper part of a screen at the reproduction of a VTR by inhibiting a burst extraction for a period from the head changeover of the VTR till a horizontal synchronizing signal or a burst signal is made stable. CONSTITUTION:Only a vertical synchronizing signal is extracted from a vertical synchronizing output of a vertical synchronizing separator circuit 5 to reset a counter 6. The counter 6 counts the signal from the extracted signal till a position of, e.g. 10H preceding position from the start position of a succeeding vertical synchronizing signal, inputs a set pulse to a pulse generating circuit 7 to generate an inhibit pulse from nearly 10 preceding horizontal period of the start position of the vertical synchronizing signal so as to prevent an output from a burst gate pulse generating circuit 2 from passing through a burst extraction circuit 3. Then extraction of burst located at a position after a changeover position of a head of preceding 5-8H from the start position of the vertical synchronizing signal is avoided at VTR reproduction. Thus, the hue change on the upper part of the screen after the head changeover of the VTR is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a burst gate control circuit that extracts only the burst portion from a color signal of a color television receiver and uses it for APC detection, killer detection, etc.

Conventional technology In recent years, with the spread of video tape recorders (VTR),
It has become necessary for color television receivers to be able to receive not only color television broadcasts but also VTR playback signals.

A conventional burst gate circuit will be explained below with reference to the drawings.

FIG. 2 shows a conventional burst gate circuit.

In FIG. 2, reference numeral 1 denotes a horizontal synchronization separation circuit that separates only the horizontal synchronization signal from the composite video signal. Reference numeral 2 denotes a burst gate generation circuit for extracting a burst signal in the bank porch portion of the composite video signal using a horizontal synchronizing signal. Reference numeral 3 denotes a circuit that uses the burst gate pulse output from the burst gate pulse generation circuit 2 to extract only the burst included in the color signal. 4 is an APC used for color synchronization of the chroma circuit using only the extracted bursts.
This is a burst detection circuit that is used for detection or killer detection, and is a general term for the part that performs killer detection.

The operation of the burst gate circuit configured as described above will be explained.The burst gate pulse generation circuit 2 generates burst gate pulses by differentiating the horizontal synchronization separation output of the horizontal synchronization separation circuit 1. Then, a burst extraction circuit 3 extracts only the burst portion included in the color signal, and a burst detection circuit 4 performs various detections.

Problems to be Solved by the Invention However, with the above configuration, as shown in FIG. From 5 to
After the head switching position 8H ago, the horizontal synchronization signal interval deviates from the normal state, or the burst phase differs from the state before the head switching, and this vertical synchronization occurs as shown in Figure 3 (C). During the period from 5 to 8H before the signal start position to the equalization pulse period 3H before the start of the vertical synchronization signal, the burst detection output deviates greatly from the normal state, and the disturbance appears at the top of the screen, i.e. This affected the image even after the vertical synchronization signal and subsequent equalization pulse period ended, causing problems such as the hue changing at the top of the screen.

In view of the above-mentioned problems, the present invention provides a burst gate control circuit that can prevent the hue etc. from changing at the top of the screen of a color television, that is, can prevent the burst detection output from being disturbed after switching the VTR head. be.

Means for Solving the Problems To achieve this object, the burst gate control circuit of the present invention includes a vertical synchronization separation circuit that separates a vertical synchronization signal from a composite video signal, and a vertical synchronization separation circuit that is reset by the output of the vertical synchronization separation circuit, and a counter for counting synchronization signals or horizontal pulses or horizontal oscillator output; a burst gate pulse generation circuit for extracting bursts included in the color signal;
a burst extraction circuit that uses the output of the burst gate pulse generation circuit to extract bursts included in the color signal; and an inhibition pulse generation circuit that uses the output of the counter to generate an inhibition pulse for prohibiting burst gates. It consists of

Effect: With this configuration, in the inhibition pulse generation circuit,
An inhibit pulse is generated from approximately 10 horizontal periods before the start position of the vertical synchronization signal to a predetermined position (such as the end of the vertical synchronization signal or the end of the equalization pulse following the vertical synchronization signal), and By using a means such as using a prohibition pulse to prevent the output from the burst gate pulse generation circuit from passing through the burst sampling circuit, it is possible to switch the head located 5 to 8 hours before the start position of the vertical synchronization signal during VTR playback. By stopping the burst extraction after the position, the VT
After switching the R head, it is possible to eliminate hue changes at the top of the screen without causing large disturbances in burst detection.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a burst gate control circuit in an embodiment of the present invention.

Note that the same numbers 1 to 4 as in the conventional example are given the same numbers as in FIG. 2, and the explanation thereof will be omitted.

In FIG. 1, 5 is a vertical synchronization separation circuit for separating vertical synchronization signals. 6 is a counter that is reset by the output of the vertical synchronization separation circuit 5 and counts horizontal pulses, horizontal synchronization signals, or horizontal oscillator outputs, 7 is a prohibition pulse generation circuit, and 8 is a counter that receives the output of the prohibition pulse generation circuit 7 during broadcast reception. 9 is a switch that turns on/off the output of the burst gate pulse generation circuit 2.

The operation of the burst gate control circuit configured as described above will be explained below.

First, only the vertical synchronization signal (nth vertical synchronization signal) is extracted from the vertical synchronization separation output of the vertical synchronization separation circuit 5, and the counter 6 is reset. Counter 6 starts IOH from the start position of the next (n+1)th vertical synchronization signal.
before, i.e. 252.5H (262,5H-10H-2
52, 5H), and the prohibition pulse generation circuit 7
Enter cent pulse.

Then, in the inhibit pulse generating circuit 7, a pulse rises from the 10th H before the (n+1)th vertical synchronizing signal.

Next, after the counter 6 is reset by the (n+1)th vertical synchronization signal, a reset pulse is input to the prohibition pulse generation circuit 7 after counting 6H (the vertical synchronization signal period and the equalization pulse period after the vertical synchronization signal). do. Then, the output pulse of the inhibit pulse generating circuit 7 falls. In this manner, the inhibit pulse generating circuit 7 generates a pulse that rises 10H before the start of the vertical synchronization signal and falls 6H after the start of the vertical synchronization signal.

Next, the output of the inhibit pulse generating circuit 7 is input to the logic circuit 8. Here, it is a logic circuit that determines whether or not to output the output of the inhibit pulse generating circuit 7 to the switch 9 based on the television/video switching signal. In other words, when receiving television broadcasting, a logic signal from the television is input to the logic circuit 8;
outputs an output that keeps the switch 9 on, that is, the switch 9 keeps on, and the burst extraction circuit 3 performs burst extraction while maintaining the output of the burst gate pulse generation circuit 2.

Next, when the VTR signal is input, the logic signal on the video side is input to the logic circuit 8, and at this time, the switch 9 is pressed only when there is an output pulse from the inhibit pulse generation circuit 7 (from the rising edge to the falling edge). output an output that turns off the
As a result, the burst extraction circuit 3 is prohibited from extracting bursts from 10H before the start of the vertical synchronization signal to 6H after the start of the vertical synchronization signal.

As described above, according to this embodiment, the period from before head switching to when the frequency or phase of the horizontal synchronizing signal or burst signal is disturbed until the horizontal synchronizing signal or burst signal stabilizes. It is possible to prohibit sampling, keep burst detection stable, and eliminate hue changes at the top of the screen.

In this embodiment, the prohibition of burst sampling starts 10H before the vertical synchronization signal and ends 6H after the vertical synchronization signal, but the starting position of prohibition of burst sampling is before the head switching of the VTR, The end may be set anywhere as long as the signal is stable after head switching and the upper part of the screen is not affected.

Effects of the Invention As described above, the present invention provides a counter that is reset by a vertical synchronization separation output and counts horizontal pulses, etc., and a point where the horizontal synchronization signal or burst signal is stabilized even before the head of the VTR is switched using the counter output. By prohibiting burst sampling for the period up to this point, it is possible to eliminate hue changes at the top of the screen during VTR playback, and this has a great practical effect.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the burst gate control circuit of the present invention, Fig. 2 is a block diagram of a conventional burst gate control circuit, and Fig. 3 → A, B, and C are explanatory diagrams regarding head switching of a VTR. It is. 2... Burst gate pulse generation circuit, 3...
... Burst sampling circuit, 5 ... Vertical synchronization separation circuit, 6 ... Counter, 7 ... Inhibition pulse generation circuit, 8 ... Logic circuit .

Claims (2)

[Claims] (1) A vertical synchronization separation circuit that separates the vertical synchronization signal from the composite video signal, a counter that is reset by the output of the vertical synchronization separation circuit and counts the horizontal synchronization signal, horizontal pulse, or horizontal oscillator output, and a counter that is included in the color signal. Using a burst gate pulse generation circuit for extracting a burst signal and the output of the burst gate pulse generation circuit,
A burst extraction circuit extracts a burst signal contained in a color signal, and an inhibition pulse generation circuit generates an inhibition pulse for inhibiting a burst gate using the output of the counter. A burst gate control circuit is characterized in that the burst gate is prohibited from the previous head switching position to a position where head switching is stable and does not affect the upper part of a television screen. (2) Use a switch output to switch between receiving color television broadcasts and receiving playback signals from a video tape recorder, and prohibit burst gates only when playing back playback signals from a video tape recorder. The burst gate control circuit according to claim 1, characterized in that: