SU1095449A1 - Device for holding level of video signal - Google Patents

Abstract

A device for fixing the video signal level, containing an algebraic adder, the first input of which is the device input, and the output is the device output, a serially connected key, the control input of which is connected to the output of the control pulse generator, and the integrator of increased noise immunity, a block of memory and a low-pass filter, a connected sequence, but connected between the integrator's output and the second input of the algebraic adder, as well as the blanking phi A ltr connected between the output of the algebraic adder and the key input, while the recording input of the memory unit is connected to the output of the control pulse generator:

Description

The device relates to radio engineering, and specifically to television, and can be used in processing video signals, in particular in color television image receivers.

A device for fixing the level of video signals is known, in which feedback is used to improve the accuracy of fixation. This device for fixing the video signal level contains an adder switched on at the input, the output and the second input of which are connected via a series-connected switch and amplifier, and the point of connection between the switch and amplifier is connected to the zero potential bus via a storage capacitor 1.

However, such a device is characterized by low noise immunity, since to increase the degree of suppression of the background of the mains supply, the constant charge time of the capacitor is chosen to be very small, which increases the sensitivity of the device to the effects of fluctuation noise. In addition, the device has a low noise immunity to the effects of harmonic interference, for example, due to the presence of a color subcarrier in the lower-case damping interval, and to the effects of switching interference caused by switching the key.

The closest in technical essence to the invention is a device for fixing the video signal level, containing an algebraic adder, the first input of which is the device input, and the output is the device output, a serially connected key, the control input of which is connected to the output of the control pulse generator, and an integrator connected between the output and the second input of the algebraic adder 2.

The disadvantage of this device is low security from the effects of fluctuation, harmonic and switching interference.

The purpose of the invention is to improve the noise immunity of the device.

This goal is achieved by the fact that a device for fixing a video signal level containing an algebraic adder, the first input of which is the device input, and the output is the device output, a serially connected key, the control input of which is connected to the output of the control pulse generator, and the integrator, a memory block and a low-pass filter are inserted, connected in series and connected between the integrator's output and the second input of the algebraic adder, as well as a stop-filter connected between the output m of the algebraic adder and a key input, while the recording input of the memory block is connected to the output of the control pulse generator.

The drawing shows the functionality of the device for fixing the level of the video signal.

The device contains algebraic

adder 1, fencing filter 2, key 3, integrator 4, memory block 5, low-frequency filters 6, and control pulse generator 7. The inverse recording input of the memory block 5 and the control input of the key 3 are connected to the output of the generator 7 control pulses, the signal of which is synchronized, as usual, with lower-case damping or synchronizing pulses of the video signal. The second input of the algebraic adder 1 is inverting if

the integrator amplifier is non-inverting, and vice versa. The memory unit 5 is made, for example, in the form of a capacitor 8, one of the plates of which is grounded, and the other is connected to the outputs of the memory unit 5 and additionally a key 9 signal input

which is the input of the memory block 5, and the control inverse input is the recording input of the memory block 5.

The device works as follows. The first input of the algebraic adder 1 is supplied with a color television signal, while its second input is a compensating signal from the output of the low-pass filter b. This signal compensates for deviations in the level of horizontal damping pulses from zero, caused by low-frequency noise and linear distortion of the television signal in the low-frequency region. The compensating signal is generated at the time of the strobe pulse from the output of the generator 7 control pulses using the integrator 4, when

key 3. For synchronization of the pulses of the generator 7 with the input video signal, horizontal quenching or synchronizing pulses are usually used. Thus, between the output of the algebraic adder

1 and its second input is a pulsed feedback circuit, which automatically monitors the level of the compensating signal as the level of the damping pulses of the input television signal. Recording a compensating signal in memory block 5

immediately after the strobe pulse has been cut off, so that the feedback circuit is open during this pulse, due to which the voltage of the compensating signal is formed by directly integrating the output television signal transmitted through the stray filter 2 at the strobe pulse interval, which ensures effective suppression of noise in the allocation of a compensating signal, and hence a good

protection of the device from the influence of fluctuation disturbances. The low pass filter 6 is connected between the second input of the algebraic adder I and the output

memory 5 effectively suppresses switching surges in the compensating signal caused by key 3, and a blocking filter 2 connected between the output of the algebraic adder 1 and the input of key 3 eliminates the influence of the color subcarrier on the formation of the compensating signal.

At the same time, due to the presence of a block of 5 memory equivalent to the presence of a delay link, a low-pass filter and a blocking filter 2 do not reduce the stability margin of the automatic control loop, although they are included in the feedback circuit.

In memory block 5, an additional key 9 provides for the opening of the feedback circuit between the output and the second input of the algebraic adder 1 during the strobe pulse output from the generator 7, and the capacitor 8 memorizes the fault voltage for the strobe pulse time.

The use of new elements - the memory block 5, the low pass filter 6 and the blocking filter 2 makes it possible to increase security from the effects of various kinds of interference. As a result, the accuracy of fixing the level of the video signal increases, which makes it possible to improve the quality of the television signal supply via communication lines.

Claims (1)

A device for fixing the video signal level, containing an algebraic adder, the first input of which is the input of the device, and the output is the output of the device, a key connected in series, the control input of which is connected to the output of the control pulse generator, and an integrator, characterized in that, in order to increase the noise immunity , a memory block and a low-pass filter are inserted into the negro, connected in series and connected between the output of the integrator and the second input of the algebraic adder, as well as a blocking filter, connected between the output of the algebraic adder and the input of the key, while the input of the memory block record is connected to the output of the control pulse generator: