JPH08331417A - Vertical synchronizing separator circuit - Google Patents

Abstract

PURPOSE: To provide a stable vertical synchronizing separator circuit by reducing the amplitude of a noise component and preventing the malfunction of an integrating operation by narrowing the pass band of a variable low-pass filter under a weak electric field. CONSTITUTION: In the case of inputting a video signal 1a under the weak electric field, an electric field detection circuit 4 adds the size of a pedestal level while using an adder 41 during the period of an electric field gate signal 41 showing timing to perform electric field detection. Next, the average value of pedestal levels is calculated by an average circuit 42 and compared with the size of an electric field level 43a by a comparator 43. In the case of weak electric field, the noise is integrated and the average level 42 becomes a larger value than ordinary electric field time. Therefore, by setting the electric field level 43a at a value higher than the pedestal level in the ordinary electric field and optimum for a system, a switch signal 4b at the time of weak electric field is outputted. At a variable low-pass filter circuit 3, the pass band of the input video signal 1a is narrowed by the signal 4b and the noise component is removed so that the malfunction of synchronous slice can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for separating a vertical synchronizing signal of a video signal input to a video device such as a television receiver and a VTR.

[0002]

2. Description of the Related Art A conventional vertical sync separation circuit will be described below with reference to the drawings. FIG. 4 is a block diagram of a conventional vertical sync separation circuit.

In FIG. 4, reference numeral 1 is a synchronous slice circuit. Reference numeral 11 denotes a comparator, which compares the level of the input video signal 1a with the slice setting level 11a of the sync signal, and outputs the composite sync signal 1b. 2 is an integrating circuit. 21
Is an up / down counter, and a clock 2 synchronized with the input video signal 1a when the composite sync signal 1b is at a high level.
At 1a, the countdown is performed, and when the level is low, the countup is performed and the count output 21b is output. Reference numeral 22 denotes a comparator, which compares the count output 21b with the set value 22a and outputs it as a vertical synchronization signal 2b.

The operation of the conventional vertical sync separation circuit configured as described above will be described with reference to FIG.

In order to separate the sync signal portion of the input video signal 1a, the comparator 11 compares the magnitude with the preset slice setting level 11a to obtain a composite sync signal 1b. In the integration circuit, this composite sync signal 1
By operating b as the count control signal of the up / down counter 21, the up / down counter performs the down / up operation when the composite signal is at the high level / low level.
b and the count output 21b that increases during the vertical synchronizing signal period
The magnitudes of will be widely separated.

Therefore, by properly setting the set value 22a, it becomes possible to separate the vertical synchronizing signal 2b as a result of the magnitude comparison in the comparator 22.

[0007]

However, in the above configuration, when the input video signal 1a is a signal in a weak electric field, the sliced composite synchronizing signal 1 is
In b, the influence of noise appears, and in the operation of the up / down counter 21 in the integrating circuit 2, the down operation is performed in the vertical synchronization period in which the up operation is originally continuous.
There is a problem that the timing at which the count output 21b reaches the set value 22a is greatly delayed or is not reached, and the vertical sync signal cannot be separated stably.

In view of the above problems, the present invention detects the electric field of the input video signal 1a and changes the pass band of the video signal according to the result to remove the noise component,
Provided is a vertical sync separation circuit that enables stable separation of a vertical sync signal even with an input video signal in a weak electric field.

[0009]

In order to solve the above problems, a vertical sync separation circuit of the present invention includes an electric field detection circuit for detecting an electric field of an input video signal and outputting a switching signal depending on the strength of the electric field. A variable low-pass filter circuit that outputs a band-limited video signal by changing the pass band of the video signal according to the switching signal, and a sync slicer circuit that slices the sync signal of the band-limited video signal and outputs a composite sync signal And an integration circuit for integrating the vertical synchronization period of the composite synchronization signal and outputting the vertical synchronization signal.

Furthermore, a function of changing the slice level of the synchronous slice circuit by a switching signal output from the electric field detecting circuit is added.

[0011]

According to the present invention, even if a video signal is input to a weak electric field, the electric field detection circuit narrows the pass band of the variable low-pass filter to reduce the amplitude of the noise component even when the video signal is input to the weak electric field. The effect of noise components in the composite sync signal can be suppressed, malfunction of the integrating circuit can be prevented, and stable vertical sync signal separation can be achieved.

Further, by varying the slice setting level in the synchronous slice circuit according to the switching signal which is the output of the electrolytic detection circuit, it becomes possible to more stably separate the vertical synchronizing signal even when a weak electric field is input.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A vertical sync separation circuit according to an embodiment of the present invention will be described below with reference to the drawings. 1 is a block diagram of a vertical sync separation circuit according to a first embodiment of the present invention.

In FIG. 1, the synchronous slicing circuit 1 and the integrating circuit 2 have the same structure as the conventional example. An electric field detection circuit 4 is shown in the block diagram of FIG.

In FIG. 2, reference numeral 41 denotes an adder, which adds the magnitudes of the input amplitudes in the period of the electric field gate signal 41a indicating the period in which the video signals are not multiplexed in the vertical blanking period and outputs the addition output 41b. Output. An averaging circuit 42 averages the addition output 41b every N frames and outputs an average output 42b. Reference numeral 43 denotes a comparator, which compares the average output 42b with the electric field level 43a to determine the state of the electric field and outputs the switching signal 4b.

Returning to FIG. 1, reference numeral 3 is a variable low-pass filter, which outputs a band-limited video signal 3b whose pass band is switched according to a switching signal. The operation will be described with reference to FIG.

When a video signal 1a in a weak electric field as shown in FIG. 3 is input, the electric field detecting circuit 4 determines the magnitude of the pedestal level during the gate period during the electric field gate signal 41a indicating the timing of electric field detection. The averaging circuit 42 calculates the average level 42 of the pedestal. The magnitude of the average level 42 and the electric field level 43a is determined by the comparator 43. If the electric field is weak, noise is integrated, and the average level 42 has a larger value than that when the normal electric field is input.

Therefore, the electric field level 43a is set to be larger than the pedestal level in the normal electric field and set to an optimum value for the system to detect the weak electric field and to perform the switching signal 4
Output b. The variable low-pass filter circuit 3 narrows the pass band of the input video signal 1a by the switching signal 4b, and removes the noise component contained in the video signal 1a at the input in the weak electric field. Therefore, when slicing the synchronizing signal of the signal 3b input by the synchronizing slice circuit 1, malfunction of the slice due to noise components can be prevented, and the integrating circuit 2 in the next stage can be prevented.
It is possible to more stably operate the integration operation in.

Further, the size of the slice setting level 11a of the synchronous slice circuit 1 is not a fixed value but the switching signal 4
By making the set value larger than the setting of the normal electric field in the weak electric field by b, it is possible to realize a more stable vertical sync separation circuit without malfunction.

[0020]

As described above, according to the present invention, an electric field detection circuit for detecting an electric field of an input video signal and outputting a switching signal depending on the strength of the electric field, and a pass band of the video signal is changed by the switching signal. A variable low-pass filter circuit that outputs a band-limited video signal, a sync slice circuit that slices the sync signal of the band-limited video signal and outputs a composite sync signal, and a vertical synchronization period of the composite sync signal are integrated. By providing an integrator circuit that outputs a vertical synchronization signal,
It is possible to realize a stable vertical sync separation circuit that does not cause malfunction of integration operation due to noise even with an input video signal in a weak electric field.

[Brief description of drawings]

FIG. 1 is a block diagram of a vertical sync separation circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of an electric field detection circuit in the same circuit.

FIG. 3 is a timing diagram showing the operation of vertical sync separation in a weak electric field.

FIG. 4 is a block diagram of a conventional vertical sync separation circuit.

FIG. 5 is a timing chart showing the operation of vertical synchronization separation in the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 synchronous slice circuit 2 integration circuit 3 variable low-pass filter circuit 4 electric field detection circuit 11 comparator 21 up-down counter 22 comparator 41 adder 42 averaging circuit 43 comparator

Claims (2)

[Claims] 1. An electric field detection circuit for detecting an electric field of an input video signal and outputting a switching signal depending on the strength of the electric field, and a band-limited video signal by varying a pass band of the video signal by the switching signal. Variable low-pass filter circuit, sync slice circuit for slicing the sync signal of the band-limited video signal to output a composite sync signal, and integrating circuit for integrating a vertical sync period of the composite sync signal and outputting a vertical sync signal A vertical sync separation circuit characterized by comprising: 2. The vertical sync separation circuit according to claim 1, wherein the slice level of the sync slice circuit is varied by a switching signal output from the electric field detection circuit.