JPS6334370Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an AGC amplification circuit for television signals.

In order to record a television signal as a hard copy, the television signal is applied to a television image processing circuit for digital processing, and this digitized data is used to operate a print control circuit that drives a printing mechanism such as an inkjet. That's what I do. In this case, the television image processing circuit uses the circuit shown in FIG. 1 to separate the television signal into R, G, and B color signals prior to digitization. In FIG. 1, 1 is an input terminal into which the video demodulation circuit output of a television receiver is input, 2 is a bandpass filter that separates subcarrier components from the input terminal output, and 3 is a luminance signal component from the input terminal output. 4 is a color demodulation circuit that reproduces the color difference signal from the subcarrier component; 5 is an AGC amplification circuit that adjusts the level of the luminance signal component; 6 is an R circuit that inputs the color difference signal and the luminance signal; , G, and B color signals. Use here
It is desirable that the AGC amplification circuit 5 be of a type that can respond to input fluctuations with a fast cycle, but in the case of leading value type AGC or keyed type AGC used in conventional television receivers, etc., the AGC amplifying circuit 5 is not provided in the system. Since the time constant of the integrating circuit is large, it has the disadvantage of poor response.

The present invention aims to provide an AGC amplification circuit that can appropriately respond to input fluctuations with a fast cycle.
The explanation will be based on the waveform diagram of each part in the figure.

A luminance signal (FIG. 3a) containing a composite synchronization signal is input to the input terminal 10. This input signal (television signal) is input to a level control circuit 11 such as a variable gain amplifier whose gain is controlled by a control signal to be described later, and the output of the level control circuit is sent to an output terminal 12, a sync separation circuit. 13, and the DC regeneration circuit 14. The synchronization separation circuit 13 separates a vertical synchronization signal and a horizontal synchronization signal, and the horizontal synchronization signal (FIG. 3b) is on the other hand sent to a clamp pulse forming circuit 15 including a delay circuit to form a clamp pulse (FIG. 3c). and, on the other hand, to a sampling pulse forming circuit 16 which allows a monostable multivibrator to form the sampling pulses (e). As shown in the figure, the clamp pulse forming circuit 15 creates a clamp pulse that indicates a position corresponding to the back porch of the horizontal synchronizing signal (the burst signal in this part has been removed by the low-pass filter shown in FIG. 1), while forming a sampling pulse. The circuit 16 is adapted to generate a sampling pulse that indicates a position corresponding to the synchronization tip. The DC component regeneration circuit 14 inputs the output of the level control circuit 11 and the output of the clamp pulse forming circuit 15, and derives a DC component regeneration output (FIG. 3 d) in which the pedestal level of the input signal (FIG. 3 a) is aligned. That's what I do. This DC component regeneration circuit 1
4 output and the output of the sampling pulse forming circuit 16, the sample hold circuit 17 extracts a signal at a position corresponding to the sampling pulse from the DC component regenerated output and holds the extracted signal for at least one horizontal period. An output signal as shown in FIG. 3f is derived. The output of this sample and hold circuit 17 is applied to one input (inverting input) 19 of a comparison amplifier 18 constituted by an operational amplifier, and a reference potential source applied to the other input (non-inverting input) 20 of the comparison amplifier 18. It is compared with the reference voltage from 21. The output of this comparison amplifier 18 (FIG. 3g) is used as a control signal for the level control circuit 11. 22 is a circuit that applies this control signal to the level control circuit 11.

In such a circuit according to the present invention, the synchronization leading edge of each horizontal synchronization signal of the input television signal is extracted and held after the television signal is pedestally clamped, and the hold voltage is compared with a reference voltage to determine the error voltage. Since the signal is amplified and used as a control signal, the AGC has quick response and is practical.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a video processing circuit in which the circuit of the present invention is used, FIG. 2 is a block diagram of an embodiment of the circuit of the present invention, and FIG. 3 is a waveform diagram of each part of the same block diagram. Explanation of main drawing numbers, 10...Input terminal, 11...
Level control circuit, 13... Synchronization separation circuit, 15,
16... Clamp and sampling pulse forming circuit, 14... DC component regeneration circuit, 17... Sample hold circuit, 18... Comparison amplifier, 22... Giving circuit.

Claims (1)

[Scope of utility model registration request] an input terminal for inputting a television signal; a level control circuit for controlling the level of the television signal from the input terminal based on a control signal; a synchronization separation circuit for separating a synchronization signal output from the level control circuit; a circuit that respectively forms a clamp pulse and a sampling pulse for pedestal clamping based on the horizontal synchronization signal output from the separation circuit; a DC regeneration circuit that receives the television signal and regenerates a DC component based on the clamp pulse; and the DC regeneration circuit. a circuit that receives a circuit output and samples and holds each synchronization tip of the horizontal synchronization signal based on the sampling pulse; a comparison amplifier that uses the sample and hold circuit output as one input and a reference potential source output as another input; an AGC amplifier circuit comprising: a circuit for applying a comparison amplifier output as the control signal to the level control circuit.