JPS5816382B2 - Eizou Shingo Clamp Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video signal clamp circuit, and more particularly to a video signal clamp circuit that can obtain a video signal clamped to a constant value.

Conventionally, keying clamps, feedback clamps, and the like are often used as methods for clamping video signals.

However, when these circuits are used to clamp the back porch of a color video signal, even if it is a soft clamp, the clamp potential changes every horizontal period due to the influence of the color burst signal, and the clamp potential changes with respect to the clamp pulse. When the phase of the burst signal shifts, the clamp potential changes during that time.

In addition, the clamp is unable to fully respond to fluctuations in the DC component of the input signal, resulting in fluctuations of 22,771 degrees, and especially when the DC component changes suddenly, there is a drawback that this can cause screen disturbance.

FIG. 1 is a block diagram of a conventional clamp circuit, and is a block diagram illustrating the operation of the clamp circuit when feedback clamping the back porch of a color video signal, which has conventionally caused the most problems.

In the figure, 1 is an input terminal for a video signal, and 2 is a date Hals a input terminal for clamping synchronized with the video signal of the video signal input terminal 1.

3 is a buffer amplifier circuit, and this buffer amplifier circuit 3
sends out the input signal with low output impedance.

Reference numeral 4 designates a sample-and-hold circuit, and this sample-and-hold circuit 4 opens its gate during the period when a pulse is present at the input terminal 2 of the clamp Date Hals, samples the potential of the buffer amplifier circuit 3, and samples the potential of the buffer amplifier circuit 3 until the next gate pulse arrives. Hold.

Reference numeral 5 denotes a DC amplifier circuit, which amplifies the output voltage of the sample and hold circuit 4 and provides negative feedback to the input signal of the video signal input terminal 1.

6 is an output terminal. Although not shown in the drawings, in order to reduce the influence of the color burst signal of the input signal, a filter that resonates with the color subcarrier frequency is often installed at the input of the sample and hold circuit 4.

In the conventional clamp circuit configured in this manner, a video signal with a fixed back porch is obtained from the output terminal 6 by means of a field pack loop.

However, due to many reasons such as there is a limit to the performance of the filter input to the sample and hold circuit 4, the input burst signal waveform is subject to distortion in an actual line, and there is a limit to the gain of the feedback loop. , the clamp potential changes due to the influence of the input burst signal and fluctuations in the DC component of the input signal.The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology by adjusting the color burst signal and input signal. It is an object of the present invention to provide a video signal clamp circuit that can always maintain a predetermined location of a video signal at a constant potential even when the DC component varies.

The present invention detects a clamp error voltage included in a clamped video signal, adds the detected clamp error voltage with the opposite polarity to the clamp error voltage included in the video signal, and adds the detected clamp error voltage to the clamp error voltage included in the video signal. It is an object of the present invention to provide a video signal clamp circuit characterized in that a video signal clamped to a constant value can be obtained by removing a 2-amp error.

. Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows an embodiment of the video signal clamp circuit according to the present invention, and a feedback clamp will be explained in order to correspond to FIG. 1.

In FIG. 2, the same reference numerals as in FIG. 1 indicate the same circuits and the same terminals, and since their operations are the same, their explanations will be omitted.

In FIG. 2, 1 is a phase inversion circuit, and this phase inversion circuit 1 receives the output voltage of the sample and hold circuit 4,
The polarity of this output voltage is reversed.

8 is a mixing circuit, and this mixing circuit 8 adds the output voltage of the phase inversion circuit 1 to the output video signal of the buffer circuit 3.

At the same time, the output of the mixing circuit 8 is sent to the output terminal 6.

In the video signal clamp circuit with the above configuration, the output voltage of the sample and hold circuit 4 is input to the phase inversion circuit 1. A change in the potential at the clamp point that is changing due to fluctuations or the like appears, that is, an error voltage.

The polarity of this error voltage is inverted in the phase inversion circuit 7 and added to the video signal in the mixing circuit 8. However, since the mixing circuit 8 contains an error voltage with a polarity opposite to that of the output of the phase inversion circuit I, Error components are removed from the output of the mixing circuit 8.

Therefore, a video signal clamped to a constant value is always obtained from the output terminal 6.

In FIG. 2 showing the embodiment of the present invention, for convenience of explaining the principle, the phase inversion circuit 1 and the mixing circuit 8 are separate circuits, but if a differential amplifier circuit is used for the mixing circuit 8, the phase inversion circuit 1 and the mixing circuit 8 can be used. Circuit 7 can be omitted.

Also, whether all circuits are DC coupled or AC coupled is determined depending on the purpose of the clamp.

The present invention is not limited to this embodiment, and various applications and modifications can be considered.In this embodiment, the case of feedback clamp has been explained, but also in the case of keying clamp, the error after clamping is taken out, If they are added in reverse phase, exactly the same effect as the feedback clamp can be obtained.

As explained above, if the video signal clamp circuit according to the present invention is used, a video signal that is always clamped to a constant value can be obtained from the output terminal. The problem of the clamp potential changing due to minute fluctuations can be solved with a very simple circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional clamp circuit, and FIG. 2 is a block diagram showing an embodiment of a video signal clamp circuit according to the present invention. 1... Video signal input terminal, 2... Clamp gate pulse input terminal, 3... Buffer amplifier circuit, 4
...sample hold circuit, 5...DC amplifier circuit,
6... Output terminal, T... Phase inversion, 8... Mixing circuit.

Claims (1)

[Claims] 1 a buffer amplifier circuit that receives a video signal including a burst signal; a sample hold circuit that receives the output of the buffer amplifier circuit and samples and holds the back porch of the video signal; and a sample hold circuit that receives the output of the buffer amplifier circuit and samples and holds the back porch of the video signal; and a mixing circuit that inverts the phase of the output of the sample and hold circuit and adds it to the output of the buffer amplifier circuit, and extracts the clamped video signal from the mixing circuit. video signal clamp circuit.