JPH09130647A - Video signal clamper and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To clamp a video signal effectively. SOLUTION: A change in a level of a horizontal synchronizing signal included in an input video signal 1 is detected by a synchronizing separator means 4 and a synchronizing signal detection means 6, converted into a DC voltage to obtain a reference potential control signal 7. A reference potential of a SYNC tip clamp means 8 is varied so as to make a pedestal potential of an output video signal 3 constant by using the reference potential control signal 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clamp device and method for fixing a DC potential of a video signal to a constant value.

[0002]

2. Description of the Related Art Conventionally, in a video equipment such as a video tape recorder which records and reproduces a video signal, in the signal processing process of the video signal, the DC potential does not change even if the level of the video signal changes. Clamping devices that are fixed to the are generally widely used.

As a video signal clamping device, a sync tip clamp for fixing the bottom of the horizontal synchronizing signal included in the video signal and a pedestal clamp for fixing the back porch portion of the horizontal synchronizing signal are generally widely used. Has been done.

In particular, due to the high image quality of the video tape recorder, the signal processing process of the video signal becomes complicated, and the clamp device to be used properly uses the sync tip clamp and the pedestal clamp according to the intended use of the signal processing. The use of a large number of clamp devices is a factor that complicates the entire video signal processing device.

[0005]

In the conventional video signal clamp device, the sync tip clamp device shown in FIG.
Since the sync tip portion 51 included in the input video signal 45 shown in FIG. 2 is aligned with the sync tip potential 48, the level of the input video signal changes from the input video signal 46 to the input video signal 4
7 changes, the pedestal potential, which is the reference of the black level of the video signal, changes from the pedestal potential 49 for the input video signal 46 to the pedestal potential 50 for the input video signal 47. There is a problem that it cannot be used in the video signal processing process with the electric potential as a reference.

Further, in the pedestal clamp device, there is a problem that the clamp device is apt to be complicated because the clamp device generally has a feedback system for detecting a DC potential component of a video signal and comparing it with a reference potential. It was

Further, when the back porch portion, which is a part of the horizontal synchronizing signal of the video signal, is fixed to the clamp potential by the clamp pulse signal, the back porch portion is damaged,
There is a problem that the back porch portion, which is a part of the horizontal synchronizing signal included in the video signal, is easily deteriorated.

The present invention solves the above problems, and the structure of the clamp device can be simplified by using the sync-tip clamp system which does not have a feedback system in the device, and is included in the video signal. By detecting the level of the horizontal sync signal and changing the reference potential of the sync tip, the pedestal potential, which is the reference of the black level of the video signal, does not change even if the level of the video signal changes. It is an object of the present invention to provide a video signal clamping device and method which do not suffer from signal deterioration of the back porch portion of the horizontal synchronizing signal included in the video signal because the use of the video signal is not restricted and the clamp pulse is not required.

[0009]

In order to achieve this object, in a video signal clamping device of the present invention, a horizontal sync signal separating means for separating a horizontal sync signal from a video signal and an output signal of the horizontal sync signal separating means are used. A sync signal level detecting means for detecting the level of the horizontal sync signal portion of the video signal based on a certain horizontal sync signal and the video signal, and a sync chip for fixing the DC potential of the video signal using the output signal of the sync signal level detecting means as an input. A clamp means is provided, and by the horizontal synchronizing signal and the video signal which are the output signals of the horizontal synchronizing signal separating means,
The sync signal level detection means detects the level of the horizontal sync signal portion of the video signal, and the sync tip clamp means fixes the DC potential of the video signal using the output signal of the sync signal level detection means as an input.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a horizontal synchronizing signal separating means for separating a horizontal synchronizing signal from a video signal, and a horizontal synchronizing signal and an image which are output signals of the horizontal synchronizing signal separating means. A sync signal level detecting means for detecting the level of the horizontal sync signal portion of the video signal by the signal; and a sync tip clamp means for fixing the DC potential of the video signal with the output signal of the sync signal level detecting means as an input. The horizontal sync signal separating means acts to separate and detect the horizontal sync signal included in the video signal, and the sync signal detecting means detects the level change of the video signal of the horizontal sync signal included in the video signal. It is detected as a level change, and the level change of the video signal acts as a change in the DC potential to operate. Voltage direction Le potential becomes constant in accordance with the level change of the horizontal synchronizing signal portion included in the image signal, the output of the synchronizing signal detecting means, acts to change the clamp reference potential.

According to the second aspect of the present invention, the level of the horizontal synchronizing signal portion included in the video signal is detected and the reference potential of the sync chip is changed, so that the video signal level changes. The pedestal potential, which is the reference of the black level of the signal, is not changed, the level of the horizontal sync signal part included in the video signal is detected, and the clamped video signal is detected according to the level change of the horizontal sync signal part. By changing the reference potential of the sync tip so that the DC potential of the pedestal part, which is a part of Acts like.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a video signal clamp device according to an embodiment of the present invention.

The input video signal 1 (37 in FIG. 4, 41, 43 in FIG. 5, 45, 46, 47 in FIG. 6) is supplied to the capacitor 2, the synchronizing signal separating means 4 and the synchronizing signal detecting means 6.

The input video signal 1 passing through the capacitor 2 is
The sync tip portion of the video signal 1 is fixed to the clamp potential set by the sync tip clamp means 8 and output as the output video signal 3.

In the synchronizing signal separating means 4, as shown in FIG. 4, the horizontal synchronizing signal 38 (FIG. 1,
In FIG. 2, 5) is output.

In the sync signal detecting means 6, the input video signal 1
By holding the respective potentials of the sync tip level and the back porch level in the horizontal synchronizing signal section of, and detecting the held potential difference, the reference control voltage 42 is output at the level of the input video signal 41 as shown in FIG. , Input video signal 43
The reference potential control signal 7 is output as the change of the DC voltage component according to the level of the input video signal 1 so that the reference control voltage 44 is obtained at the level of.

In the sync tip clamp means 8, when the reference potential control signal 7 increases (when the level of the input video signal 1 increases), the DC reference potential to be clamped decreases and the reference potential control signal 7 decreases. At this time (when the level of the input video signal 1 decreases), the clamped DC reference potential changes in an increasing direction, and the amount of change is set so that the pedestal potential of the output video signal 3 becomes constant.

FIG. 2 is a block diagram of the sync signal detecting means 6, in which the horizontal sync signal 5 is supplied to the capacitors 17 and 18, and the input video signal 1 is supplied to the analog switches 24 and 25.

The capacitors 17, 18 and the resistors 9, 12 and the diodes 22, 23 obtain the falling detection signal 39 and the rising detection signal 40 of the horizontal synchronizing signal 5 as shown in FIG.

The fall detection signal 39 coincides with the timing of the sync tip portion of the horizontal synchronizing signal 38, and the fall detection signal 40 coincides with the timing of the back porch portion of the horizontal synchronizing signal 38.

Further, the falling detection signal 39 is the resistor 1
After the polarity is inverted by 0 and the transistor 21, it is supplied to the analog switch 24, and the rising detection signal 40 is supplied to the analog switch 25 as it is.

The analog switch 24 receives the input video signal 1
The sink chip portion of the
Then, the voltage of the sync tip portion is charged and the potential is held.

The analog switch 25 is for input video signal 1
It becomes conductive at the back porch part of the capacitor 20
Then, the electric charge is charged to the voltage of the back porch portion and the potential is held.

The potential of the capacitor 19 is set to the resistors 13, 1
After being divided by 4, the voltage is supplied to the positive-phase input of the operational amplifier 26, and the potential of the capacitor 20 is divided by the resistors 15 and 16 and then supplied to the negative-phase input of the operational amplifier 26 to obtain the reference potential control signal. It is output as 7.

FIG. 3 is a block diagram of the sync tip clamp means 8, which comprises resistors 27, 28 and 29 and an operational amplifier 35.
The inputted reference potential control signal 7 is inverted and the resistor 30
Operates so that the reference potential set by the resistors 31, 32 and the capacitor 34 changes, and the sync tip portion of the input video signal is clamped by the transistor 36 to obtain the output video signal 3.

As described above, in the present embodiment, the reference potential of the sync tip is changed according to the level of the input video signal 1 to keep the pedestal potential of the clamped output video signal 3 constant. A video signal clamp device having a simple structure can be provided.

Further, since the clamp pulse is not used, there is no deterioration of the video signal due to the clamp pulse.

[0028]

As described above, by using the sync tip clamp, by changing the reference potential of the sync tip so that the pedestal potential of the video signal after the clamp is kept constant, the conventional pedestal clamp can be obtained. A simple video signal clamping device and method having no feedback system can be provided.

Further, since the clamp pulse is not used, there is an excellent feature that there is no deterioration of the video signal due to the clamp pulse.

[Brief description of the drawings]

FIG. 1 is a block diagram of a video signal clamp device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a synchronization signal detecting means 6 according to an embodiment of the present invention.

FIG. 3 is a configuration diagram of a sync tip clamp means 8 according to an embodiment of the present invention.

FIG. 4 is a signal waveform diagram of each part of the synchronization signal detecting means in the embodiment of the present invention.

FIG. 5 is a signal waveform diagram of each part of the sync tip clamp means according to the embodiment of the present invention.

FIG. 6 is a signal waveform diagram of a conventional sync tip clamp means.

[Description of Reference Signs] 1 input video signal 2, 17, 18, 19, 20, 34 capacitor 3 output video signal 4 sync signal separating means 5,38 horizontal sync signal 6 sync signal detecting means 7 reference potential control signal 8 sync tip clamp means

Claims (2)

[Claims] 1. A horizontal sync signal separating means for separating a horizontal sync signal from a video signal, and a level of a horizontal sync signal portion of the video signal by a horizontal sync signal and a video signal which are output signals of the horizontal sync signal separating means. A video signal clamp device comprising: a sync signal level detection means for detecting; and a sync tip clamp means for fixing a DC potential of a video signal with an output signal of the sync signal level detection means as an input. 2. A pedestal potential that serves as a reference for a black level of a video signal even if the level of the video signal changes by detecting the level of a horizontal sync signal portion included in the video signal and changing the reference potential of the sync tip. Video signal clamping method that does not change.