JP3239437B2 - Horizontal sync signal detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver including a circuit for detecting television signals and video signals.

[0002]

2. Description of the Related Art In recent years, a horizontal synchronizing signal detecting circuit for detecting the presence or absence of a television signal or a video signal is indispensable in a television receiver in order to prevent the automatic channel selection function and the noise screen erasing function (blue back function) from operating. Is coming. conventionally,
A method for determining whether the horizontal AFC circuit is locked or unlocked is used as a horizontal synchronization signal detection circuit.
Hereinafter, an example of a conventional horizontal synchronization signal detection circuit will be described with reference to the drawings. In FIG. 2, 1 is a horizontal synchronizing signal, 2 is a horizontal AFC circuit, 3 is a horizontal oscillation circuit, 4 is an AND circuit, 5 is an integration circuit, and 6 is a voltage comparison circuit.

[0003] The operation of the horizontal synchronizing signal detecting circuit configured as described above will be described below.

When there is a horizontal synchronizing signal, the horizontal AFC circuit is in a locked state, the horizontal oscillation circuit signal becomes a signal having the same phase as the horizontal synchronizing signal, and the voltage obtained by integrating the logical product with the horizontal synchronizing signal is a voltage comparing circuit. Higher than the reference value of
It is determined that there is a horizontal synchronization signal. When there is no horizontal synchronizing signal, the logical product of the noise and the horizontal oscillation circuit signal is obtained, and the integrated voltage becomes lower than the reference value of the voltage comparison circuit. Switch to.

[0005]

However, in the above-described configuration, the horizontal AFC is partially lost when a video player is connected to a television receiver and fast-forwarding is performed in a playback state. In order to deviate from the pull-in frequency range of the circuit, the voltage obtained by integrating the logical product decreases and becomes lower than the reference value of the voltage comparison circuit. There was a problem that there was a case where it could not be seen.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a horizontal synchronizing signal detecting circuit for judging that there is a horizontal synchronizing signal even when fast-forwarding in a reproducing state.

[0007]

Means for Solving the Problems To this end, the horizontal synchronizing signal detecting circuit of the present invention, the horizontal synchronizing signal
The input horizontal AFC circuit and the horizontal AFC circuit
The input horizontal synchronization signal and the oscillation frequency have the same phase
Controlled by the horizontal oscillation circuit and the horizontal oscillation circuit
Between the horizontal oscillation signal output from the
Calculates the logical product and outputs the same phase as the input horizontal synchronization signal
And an output from the AND circuit
A first integration circuit for integrating a signal, and the first integration circuit
The output signal is compared with the reference voltage to output a detection signal.
A voltage comparison circuit for integrating the input horizontal synchronizing signal.
Output from the second integrating circuit and the voltage comparing circuit.
A detection signal and an output signal output from the second integration circuit
And an OR circuit for calculating the logical sum of
Before the horizontal sync signal that is input with part of the signal missing
The integration signal output from the second integration circuit is the OR signal.
The second integrating circuit so as to be higher than the threshold value of the road.
The time constant of
The voltage of the detection signal output from the voltage comparison circuit is synchronized horizontally.
Even before it falls below a predetermined voltage level indicating the presence of a signal
A predetermined signal indicating the presence of the horizontal synchronizing signal is output from the second integrating circuit.
A bell voltage is supplied to the OR circuit.
Outputs the correct judgment signal with input horizontal sync signal
It is characterized by doing so.

[0008]

With the above arrangement, even if a horizontal synchronizing signal is partially lost during fast-forwarding in the reproducing state, the integration time is adjusted so that the signal obtained by integrating the horizontal synchronizing signal becomes higher than the threshold value of the OR circuit. By setting a constant, the logical sum is HIGH
And it can be determined that there is a horizontal synchronization signal.

[0009]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a horizontal synchronizing signal detecting circuit according to an embodiment of the present invention. In FIG. 1, the same components as those in the conventional example shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The present embodiment differs from the conventional example in the configuration in which the logical sum of the output signal of the voltage comparison circuit and the signal obtained by integrating the horizontal synchronizing signal is added.

The horizontal synchronizing signal detecting circuit configured as described above will be described. By setting the integration time constant so that the signal obtained by integrating the horizontal synchronizing signal becomes higher than the threshold value of the OR circuit, even if the horizontal synchronizing signal is partially lost when fast-forwarding in the playback state. The logical sum becomes HIGH, and it can be determined that there is a horizontal synchronization signal, so that the reproduced image can be viewed.

[0013]

As described above, according to the present invention, the signal obtained by integrating the logical product of the horizontal synchronizing signal and the horizontal oscillation circuit signal controlled by the horizontal AFC circuit and comparing the voltage is compared with the signal obtained by integrating the horizontal synchronizing signal. By judging the presence or absence of a horizontal synchronizing signal from the logical sum, a video player is connected to the television receiver, and it is judged that there is a horizontal synchronizing signal even when fast-forwarding in the playback state, and the reproduced image is viewed. Can be.

[Brief description of the drawings]

FIG. 1 is a horizontal synchronization signal detection circuit according to an embodiment of the present invention.

FIG. 2 is a conventional horizontal synchronization signal detection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Horizontal synchronizing signal 2 Horizontal AFC circuit 3 Horizontal oscillation circuit 4 AND circuit 5, 7 Integration circuit 6 Voltage comparison circuit 8 OR circuit

Claims (1)

(57) [Claims] 1. A horizontal AFC circuit to which a horizontal synchronization signal is input.
And the input horizontal synchronization signal by the horizontal AFC circuit.
And horizontal oscillation controlled so that the oscillation frequency is the same
Oscillation circuit, and a horizontal oscillation signal output from the horizontal oscillation circuit.
Signal and the input horizontal synchronizing signal, and
AND circuit for outputting a signal having the same phase as the horizontal synchronization signal
And a first product for integrating an output signal from the AND circuit
A dividing circuit and a voltage output from the first integrating circuit.
A voltage comparison circuit that outputs a detection signal by comparing with a reference voltage;
A second integration circuit for integrating the input horizontal synchronization signal;
A detection signal output from the voltage comparison circuit and the second product
OR for calculating the logical sum of the output signals output from the branch circuit
Circuit and a horizontal
Integral output from the second integration circuit for the period signal
So that the signal is higher than the threshold value of the OR circuit.
The time constant of the second integration circuit is set, and the input horizontal synchronization signal is set.
Detection signal output from the voltage comparison circuit due to lack of
Is higher than a predetermined voltage level indicating the presence of the horizontal sync signal.
The horizontal synchronizing signal from the second integrating circuit.
A voltage of a predetermined level indicating the presence is supplied to the OR circuit.
From the OR circuit to determine whether there is an input horizontal synchronization signal.
A horizontal synchronizing signal detection circuit wherein a constant signal is output .