JPS6190573A - Feedback clamp circuit of television signal - Google Patents

Abstract

PURPOSE:To attain a stable action with respect to a level fluctuation by utilizing a voltage obtained by integrating a horizontal synchronizing signal as a separation/comparison reference signal of a horizontal synchronizing component separator circuit. CONSTITUTION:The output voltage of a comparator 3 is integrated by an integration circuit composed of a resistance 9 and capacitor 10, and its integrated voltage is inputted to an inversion amplifier 11, whose output DC voltage is used as a reference voltage of the comparator 3. Consequently, since the voltage in proportion to the output pulse width of the comparator 3 goes to a reference voltage, it drops due to the narrow pulse interval when a vertical synchronizing pulse is inputted, whereby the comparators 3 will not execute an erroneous action. In such a manner a horizontal synchronizing pulse is properly detected to control a changeover switch 7, and the voltage subjected to the sample hold by an operation amplifier 5 is fed back to a differential amplifier 8. Then the difference between input signals is taken and made a horizontal synchronizing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a feedback clamp circuit for television signals, and more particularly to a feedback clamp circuit for television signals that operates stably against level fluctuations.

The television signal clamp circuit referred to here is a circuit for extracting the horizontal synchronization signal of the television.

[Conventional technology]

FIG. 2 shows the image field signal. (al is the waveform that comes at the end of the second field, and fb) is the waveform that comes at the end of the first field.

In FIGS. 2(a) and 2(b), the period of 9H containing the equalization pulse and the vertical synchronization pulse is exactly the same, and the period of the horizontal pulse is the same, but the phase is shifted by 0.5H.

FIG. 3 is a diagram showing an example of a conventional television signal clamp circuit.

In the figure, l is an inverting amplifier, 2 is a simple clamp circuit, 3 is a comparator, 4 is a changeover switch, 5 is an operational amplifier, 6 is a capacitor, 7 is a resistor, and 8 is a differential amplifier. The same symbols represent the same objects throughout all the figures below.

The polarity of the television signal is inverted by an inverting amplifier 1 and clamped by a simple clamp circuit 2 using a diode. This clamped signal is input to comparator 3.

This clamped signal is compared with a constant reference voltage E in a comparator 3 to obtain a horizontal synchronization pulse at its output.

When the horizontal synchronization pulse is output, the selector switch 4 is activated for that period, sample held by the operational amplifier 5, and fed back to the differential amplifier 8. The differential amplifier 8 takes the difference from the input signal and performs horizontal synchronization. A pulse is output.

However, in the above-mentioned conventional method, when a vertical synchronizing pulse comes in, the input to the comparator 3 decreases because the pulse interval is narrow as shown in FIG. 2, so the reference voltage E is lowered. For this reason, it had the disadvantage of being weak against noise.

[Problem that the invention seeks to solve]

An object of the present invention is to eliminate the drawbacks of the conventional method described above, and to perform stable operation against level fluctuations by using an integrated voltage according to the input signal as the reference voltage of the horizontal synchronization separation circuit of the television signal clamp circuit. It is to do as you please.

Means for Solving Problem C] The means for solving the problem is to use the voltage obtained by integrating the horizontal synchronization pulse as the comparison voltage for separation of the horizontal synchronization partial forward circuit. achieved.

[Operation] According to the present invention, the horizontal synchronizing pulse of the clamp circuit of the television signal is integrated, and by utilizing the fact that the integrated voltage changes depending on the vertical synchronizing pulse portion of the pulse, the integrated voltage is used as the reference of the comparator. This has the great effect of stably clamping the television signal.

〔Example〕

FIG. 1 is a diagram showing an embodiment of a television signal clamp circuit according to the present invention.

In the figure, 9 is a resistor, 10 is a capacitor, and 11 is an inverting amplifier.

The present invention will be described in detail below with reference to the drawings.

In the present invention, the output voltage of the comparator 3 is integrated by an integrating circuit consisting of a resistor 9 and a capacitor 10, the integrated voltage is manually input to the inverting amplifier 11, and the output DC voltage of the inverting amplifier 11 is set as the reference voltage of the comparator 3. Use as.

In the conventional system, the comparator 3 compares the voltage with a constant reference voltage, but in the present invention, the voltage is compared with the output DC voltage of the inverting amplifier 11.

Therefore, the voltage proportional to the output pulse width of comparator 3 becomes the reference voltage, so when the vertical synchronization pulse is input, the pulse interval is narrow, so the reference voltage also decreases, and comparator 3
will not malfunction.

In this way, the horizontal synchronization pulse is accurately detected and the changeover switch 7 is controlled, and the voltage sampled and held by the operational amplifier 8 is fed back to the differential amplifier 8, and the difference with the input signal is taken and used as a horizontal synchronization signal.

By doing this, the comparison reference voltage of comparator 3 at times other than the vertical synchronization pulse can be changed to the conventional constant comparison reference voltage E.
By setting the value sufficiently larger than , it is possible to create a circuit that is more resistant to noise than the conventional method, and when the vertical synchronization pulse comes in, the comparison base (voltage also drops), resulting in very stable operation. is guaranteed.

〔Effect of the invention〕

As described above in detail, the present invention has the great effect of realizing a television signal feedback clamp circuit that can operate stably against level fluctuations.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of a television signal clamp circuit according to the present invention. FIG. 2 shows the image field signal. FIG. 3 is a diagram showing an example of a conventional television signal clamp circuit. In the figure, 1 is an inverting amplifier, 2 is a simple clamp circuit, 3 is a comparator, 4 is a changeover switch, 5 is an operational amplifier, 6 is a capacitor, 7 is a resistor, 8 is a differential amplifier, 9 is a resistor, 1
0 is a capacitor, and 11 is an inverting amplifier.

Claims (1)

[Claims] A television signal feedback clamp circuit characterized in that a voltage obtained by integrating a horizontal synchronizing pulse is used as a comparison reference voltage for separation in a horizontal synchronizing part separation circuit.