JPH0531473U - Video detection circuit - Google Patents

Abstract

(57) [Summary] [Construction] A video filter 1 is input to a multiplier 2, and a carrier filter 3 for extracting only a carrier from the video modulator 1 is input.
Is added to obtain a demodulation output 4. The demodulation output 4 is an impulse generated when a pulsed disturbance wave generated by the BPF 5 for extracting the image of the video signal or the synchronous component and the electric motor or the ignition device of the engine enters the antenna of the receiver. It is input to the BPF 6 that extracts noise components, and the peaks or average values of the respective outputs are detected by the wave detectors 7 and 8. [Effect] Focusing on the demodulation output, the impulse noise components for the video or sync component of the signal are compared, the bandwidth of the carrier filter is switched, the detection efficiency for a signal with a large modulation degree is changed, and the demodulation output is generated. The amplitude of impulse noise is suppressed, and a good video signal with little impulse noise can always be obtained.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a pseudo synchronous detection circuit that demodulates a video modulation wave.

[0002]

[Prior Art]

 Conventionally, in a pseudo-synchronous detection circuit for demodulating a video modulation wave, the NHK color television textbook (top) of the Nippon Broadcasting Church [October 20, 1977, P124, 5.3 Video detection circuit 5.3.2] Example of low-level video detection circuit], the carrier filter has a fixed bandwidth, and pulsed disturbance waves generated by electric motors, engine ignition devices, etc. When input to, the demodulation output also output noise proportional to the input, degrading image quality. That is, if the bandwidth of the carrier filter is set so as to suppress the amplitude of the impulse noise generated in the demodulation output, the characteristics of the video signal of the demodulation output deteriorate, and the amplitude of the impulse noise cannot be suppressed.

[0003]

[Problems to be solved by the device]

 In the present invention, focusing on the demodulation output, the impulse noise component with respect to the video or sync component of the video signal is compared, the bandwidth of the carrier filter is switched, and a signal with a large degree of modulation (100% greater than a white video signal By changing the detection efficiency with respect to (amplitude), the amplitude of impulse noise generated in the demodulated output is suppressed, and pulsed disturbance waves generated by electric motors, engine ignition devices, etc. are transmitted to the receiver antenna. The objective is to provide a good video signal with little impulse noise even when input.

[0004]

[Means for Solving the Problems]

 In order to achieve the above object, a means for extracting and detecting an impulse noise component from a demodulation output in a pseudo-synchronous detection circuit, a means for extracting and detecting a video image or a synchronization component of a signal, and a means for comparing two detection outputs And means for switching the bandwidth of the carrier filter according to the compared output.

[0005]

[Action]

 In the present invention, focusing on the demodulation output, the impulse noise components with respect to the video or sync component of the signal are compared, the bandwidth of the carrier filter is switched, and a signal with a large modulation degree (amplitude larger than a 100% white video signal is detected). ) Is suppressed, the amplitude of impulse noise generated in the demodulation output is suppressed, and the pulsed disturbance wave generated by the electric motor or engine ignition device is input to the receiver antenna. Even in the case of occurrence, it is possible to provide a good video signal with less impulse noise.

[0006]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. At the same time that the video modulation wave 1 is input to the multiplier 2, the output of the carrier filter 3 that extracts only the carrier wave from the video modulation wave 1 is added to obtain a demodulation output 4. The demodulation output 4 is generated when a pulsed disturbance wave generated by the BPF 5 that extracts the image of the video signal or the synchronization component and the electric motor or the ignition device of the engine enters the antenna of the receiver. Is input to the BPF 6 for extracting the impulse noise component, and the peak or average value of each output is detected by the detectors 7 and 8, respectively. The outputs of the detectors 7 and 8 are input to the comparator 9, and when the detection voltage 7 is higher than the detection voltage 8, that is, when the total energy of impulse noise becomes larger than that of the video signal of the demodulation output 4. The bandwidth changeover switch 10 widens the bandwidth of the carrier filter to reduce the detection efficiency for a signal having a large modulation degree. As a result, the amplitude of the impulse noise generated in the demodulation output 4 is suppressed, and even if a pulsed disturbance wave generated in an electric motor or an engine ignition device is input to the receiver antenna, the impulse noise A good video signal with less noise can be obtained.

[0007]

Effect of the Invention In the present invention, focusing on the demodulation output, the impulse noise component with respect to the image or the synchronization component of the signal is compared, the bandwidth of the carrier filter is switched, and the detection efficiency for the signal with a large modulation degree is changed. By doing so, the amplitude of the impulse noise generated in the demodulation output is suppressed, so that a good video signal with a small amount of impulse noise can always be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

[Explanation of symbols]

1-modulation wave, 2-multiplier, 3-carrier filter,
4-demodulation output, 5-bandpass filter for video or sync component extraction, 6-impulse noise component extraction bandpass filter, 7-detector, 8-detector, 9-comparator,
10-bandwidth switch

Claims (1)

[Scope of utility model registration request] 1. A pseudo-synchronous detection circuit for a television receiver, comprising means for extracting and detecting an impulse noise component generated in a demodulation output, means for extracting and detecting an image or a synchronization component of the demodulation output, A means for comparing the detection output signals and a means for switching the bandwidth of the filter for extracting the carrier wave from the video modulated wave are provided, and by switching the bandwidth of the filter by the comparison output, the detection efficiency for a signal with a large modulation degree can be improved. A video detection circuit characterized by reducing the amplitude of impulse noise generated in the demodulation output.