SU1590053A3 - Arrangement for automatic switch control of amplification in tv transmitting and relay stations - Google Patents

Abstract

This invention relates to an automatic key gain control technique in television transmitting and relay stations. The purpose of the invention is to increase the stability of the gain control. The device contains a controlled middle frequency amplifier 1, a middle frequency amplifier 2 with internal gain control, a synchronization signal separation unit 3, a gate pulse shaper 4, a middle frequency demodulation unit 5, a signal level conversion unit 6, a strobe and memory unit 7 and DC amplifier 8. The goal is achieved through the use of a two-loop gain control, which makes the operation of the device stable and independent of video information. Since the gain in the second loop (for amplifier 2) is greater than that in the main loop (for amplifier 1), a stable strobe signal can be generated even with a very low level of received input signal, and so. cannot get overload in the main loop when starting work. The required stability of the circuit design of the device m. provided with the use of modern integrated circuits. 1 hp f-ly, 2 ill.

Description

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with

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1

This invention relates to automatic gain control, in particular, to devices for automatic key gain control in television, video transmission and relay stations: chi.

The purpose of the invention is to increase the stability of the gain control.

. FIG. Figure 1 shows the structural electrical circuit of the proposed device; in fig. 2 - timing diagram of strobe pulses (sampling portions) and synchronization pulse. ; A device for automatic key gain control in television transmitting and relay stations contains a controlled gain of 1 center frequency, a center frequency amplifier 2 with internal gain control, a block 3 of the synchronization signal, a gate pulse shaper 4, a center frequency demodulation block 5 signal failure, gating and storing unit 7 and dc amplifier 8. . .

Device automatic key gain control in television

transmitting and relay stations work-Q or in a high-frequency receiver.

em as follows

The average frequency signal is fed to the input of a controlled amplifier. 1 medium frequency (first loop) and to the input of the amplifier 2 medium frequency with internal gain control (second loop). From the output of the controlled amplifier 1 of the middle frequency, the signal is fed to the input of the demodulation unit 5 sredy35

Stability can be influenced by the correct coefficient factor in the loop and by the correct choice of filar capacitors that influence the hundredth characteristic.

The second loop, i.e. input of force 2 of medium frequency, receives the impenetrable. signal of medium frequency. At tel 2 medium frequency has

frequency, which produces video-internal adjustment loop

This video signal is compliant: Zim is set by the level for gating and storing unit 7 with the help of unit 6, the signal level. If there is no video signal suitable for use, the signal level conversion unit 6 automatically switches from the signal level to the blanking level, so that the circuits are protected from overload. The strobe pulse supplied by the gating pulse shaper 4 is applied to the control, E; HIT of the strobe and hold unit 7: -, thereby selecting a portion of the video signal supplied to the strobe block and storing unit 7, and this portion is stored on the memory capacitor time period of the image line.

50

55

gain, the gain in which is greater than the gain in the main loop. Thus, the video output signal of the middle frequency amplifier 2, which drives the sync signal separation unit 3, is stable regardless of the amplitude of the input signal. The block 3 of the synchronization signal separates a sequence of constant-magnitude synchronization pulses, from which the gate generator produces a corresponding strobe-pulse and other signals necessary for the operation of the second loop. The pulses produced by the strobe pulse are fed to the control input (strobe) of the strobe block 7 and for commemoration.

As shown in FIG. 2, the thrombolt pulse is in the order of 1.2 µs; then, the synchronization pulse duration is 4.7 µs. Since the portions are taken from each synchronizing pulse, the output of the gating and memorizing unit 7 results in a DC voltage proportional to the amplitude of the average frequency signal. This DC signal is amplified (to match the gain in the loop) by the DC amplifier 8. current, the output of which controls the gain of the controlled amplifier 1 of the medium frequency.

To obtain a wider control range, the DC amplifier 8 has a gain control output, whereby the gain control range can be extended by about 10 dB. This also allows for a careful adjustment of the high-frequency receiver (not shown). Thus, the main control loop can be closed at two points: in the controlled amplifier 1 of the middle frequency

or in a high frequency receiver.

Stability can be influenced by calculating the correct gain in the loop and by choosing the right filter capacitors that affect the frequency response.

The second loop, i.e. input of amplifier 2 of medium frequency, receives an uncontrollable. signal of medium frequency. Medium-frequency amplifier 2 has its own internal adjustment loop

gain, the gain in the loop of which is greater than the gain in the main loop. Thus, the video output signal of the middle frequency amplifier 2, which drives the sync signal separation unit 3, is stable regardless of the amplitude of the input signal. The block 3 of the synchronization signal allocates a sequence of synchronous pulses of a constant value, from which the gate driver 4 produces a corresponding strobe-pulse and other signals necessary for the operation of the second loop. The strobe pulses produced are fed to the control input (strobe) of the strobe and storing unit 7.

The operation of the mid-frequency amplifier - with two-loop gain control 1- is stable and does not depend on video information. Since the gain in the second loop is greater than that in the main loop, a stable strobe signal can be generated even at a very low level of the received input signal, and thus cannot be overloaded in the main loop at the start of operation. The required stability of the circuit device can be provided by using modern integrated circuits.

Claims (1)

 1. An automatic key gain control device in television transmitting and relay stations, comprising a series-connected controlled middle frequency amplifier, a middle frequency demodulation unit and a signal level conversion unit, as well as a gating and storage unit, the control input of which connected to the first output of the gate pulse driver, and ten a controlled mid frequency amplifier, the signal input and output of which are the input and output of the device, characterized in that, in order to improve the stability of the gain control, serially connected middle frequency amplifier with internal gain control and synchronization signal block are introduced, the code of which is connected to the input of the gate pulse generator, the second output of which is connected to the control inputs of the sync signal block and the middle frequency amplifier from the internal they controlling gain input coupled to the input of the controlled amplifier medium frequency, at 20 the output of the signal level conversion unit connected to the signal input of the gating and zapomi-: nani whose output is connected to the input of the DC amplifier. 15 25 2, the apparatus according to claim 1, characterized in that the additional output of the sync signal extraction unit is connected to the secondary gate, the input of the level-DC amplifier unit, and the output port is connected to the control input signal. max. // us - Fiz.g Compiled by N. Matvienko Editor M. Bandura Tehred M. Didyk Proofreader T. Paliy 053 ten a controlled mid frequency amplifier, the signal input and output of which are the input and output of the device, characterized in that, in order to improve the stability of the gain control, serially connected middle frequency amplifier with internal gain control and synchronization signal block are introduced, the code of which is connected to the input of the gate pulse generator, the second output of which is connected to the control inputs of the sync signal block and the middle frequency amplifier from the internal they controlling gain input coupled to the input of the controlled amplifier medium frequency, at 20 the output of the signal level conversion unit connected to the signal input of the gating and zapomi-: nani whose output is connected to the input of the DC amplifier. 15 25 2, the apparatus according to claim 1, characterized in that the additional output of the sync signal extraction unit is connected to the auxiliary input, the input unit of the level signal of the nautical signal.