JPH0946644A - Video frequency characteristic correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the video frequency characteristic correction device in which variation in a video frequency characteristic is suppressed and the image quality is improved. SOLUTION: A video signal of a base band outputted from a video and voice demodulation circuit 16 is given to a burst detection circuit 21, in which a difference component is detected when a level is in excess of, e.g. 240m Vp-p or less than it, a control signal converted into a DC voltage is outputted to a frequency correction circuit 22 to control its impedance. The frequency correction circuit 22 corrects a video frequency by the control signal to feed it back to the video and voice demodulation circuit 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video frequency characteristic correction device effective for use in a reception front end device including a video tape recorder (hereinafter referred to as VTR).

[0002]

2. Description of the Related Art A conventional video frequency characteristic correction device will be described below with reference to FIG.

FIG. 2 is a block diagram of a conventional video frequency characteristic correction device. In FIG. 2, reference numeral 1 denotes an antenna input terminal for inputting a high frequency signal such as a TV broadcast signal from an antenna (not shown). Reference numeral 2 denotes an antenna output terminal, which is a terminal for outputting the high-frequency signal input to the antenna input terminal 1 through the distributor 9 and the switch circuit 10.
The antenna output terminal 2 is connected to a television receiver (not shown) through a coaxial cable. At this time, the high frequency signal output from the RF modulator 11 is output by switching the switch circuit by a control signal from the outside, that is, an antenna switching control signal. Reference numeral 9 is a distributor for distributing a high frequency signal from the antenna input terminal 1 to the tuner 14 and the switch circuit 10, and 10 is an antenna for the high frequency signal from the antenna distributor 9 and the video / audio carrier frequency signal input from the RF modulator 11. A switch circuit that switches according to a control signal input from the switch control terminal 19, and generally switches using a transistor or a diode circuit. Reference numeral 11 denotes an RF modulator for RF-modulating a video / audio signal from a recording means (not shown) of the VTR to a baseband video / audio signal obtained through a video / audio processing circuit to extract a high frequency signal. Generally, in a domestic VTR, a signal of a 1-channel or 2-channel video / audio carrier frequency is output and connected to a television receiver via a coaxial cable. Reference numeral 19 is an antenna switching control terminal that controls switching of the switch circuit 10 and outputs the TV signal from the antenna input terminal 1 or the high frequency signal from the RF modulator 11 to the antenna output terminal 2. Reference numeral 14 is a reception signal for selecting a TV signal and an intermediate frequency signal. A tuner for converting into a signal, a reference numeral 15 is an antenna tuner having an antenna section and a tuner section, a reference numeral 16 is a video / audio demodulation circuit for demodulating the video / audio intermediate wave number signal selected by the tuner 14 into a baseband signal, and 17 is a video / audio A video output terminal for outputting the baseband video signal demodulated by the audio demodulation circuit 16 and an audio output terminal for outputting the baseband audio signal demodulated by the video / audio demodulation circuit 16. Video output terminal 17 and audio output terminal 18
The signal output from is input to a video / audio signal processing means (not shown) of the VTR. Reference numeral 20 is a video / audio demodulation circuit unit for extracting a baseband video / audio signal.

[0004]

However, in the above-described conventional configuration, the impedance is constant, the RF response and the intermediate frequency output characteristic are varied in the antenna tuner section 15, and the basic channel and the video frequency characteristic between channels are also varied. There is a problem in that the image quality deteriorates due to the variation.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a video frequency characteristic correction apparatus capable of suppressing variations in video frequency characteristics and improving image quality.

[0006]

In order to achieve this object, in order to solve the above problems of the present invention, a video frequency characteristic correction circuit of the present invention is an antenna input terminal for inputting a television signal received by an antenna. And a distributor for distributing the television signal input from the antenna input terminal,
A switch circuit for switching and outputting one output signal of the distributor and an input signal from the recording / reproducing means of the video tape recorder, and a video / audio demodulation circuit for demodulating the other output signal of the distributor into video and audio signals. And a burst detection circuit that detects a burst signal in the video signal output from the video and audio demodulation circuit and outputs a control signal, and a frequency correction is performed by the control signal output from the burst detection circuit and is fed back to the video and audio demodulation circuit. And a frequency correction circuit for controlling the frequency.

[0007]

With this structure, it is possible to suppress variations in the video frequency characteristics between the basic channel and the channels and obtain a significantly improved image quality.

[0008]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a video frequency characteristic correction apparatus of this embodiment. In FIG. 1, reference numeral 1 denotes an antenna input terminal for inputting a high frequency signal such as a TV broadcast signal from an antenna (not shown). Reference numeral 2 denotes an antenna output terminal, which is a terminal for outputting the high-frequency signal input to the antenna input terminal 1 through the distributor 9 and the switch circuit 10. The antenna output terminal 2 is connected to a television receiver (not shown) through a coaxial cable. At this time, the high frequency signal output from the RF modulator 11 is output by switching the switch circuit by a control signal from the outside, that is, an antenna switching control signal. 9 is a distributor that distributes the high frequency signal from the antenna input terminal 1 to the tuner 14 and the switch circuit 10, and 10 is a switch between the high frequency signal from the antenna distributor 9 and the video and audio carrier frequency signal input from the RF modulator 11. A switch circuit that switches according to a control signal input from the control terminal 19, and generally switches using a transistor or diode circuit. Reference numeral 11 denotes an RF modulator for RF-modulating a video / audio signal from a recording means (not shown) of the VTR to a baseband video / audio signal obtained through a video / audio processing circuit to extract a high frequency signal. Generally domestic VT
In R, a signal of a video / audio carrier frequency of 1 channel or 2 channels is output and connected to a television receiver via a coaxial cable. 19 is a switching control terminal for switching control of the switch circuit 10 to output the TV signal from the antenna input terminal 1 or the high frequency signal from the RF modulator 11 to the antenna output terminal 2, and 14 is a reception signal for selecting the TV signal to be an intermediate frequency signal. A tuner for converting, 15 is an antenna tuner having an antenna section and a tuner section, 16 is a video / audio demodulation circuit for demodulating the video / audio intermediate wave number signal received and selected by the tuner 14 into a baseband signal, and 17 is video / audio. A video output terminal for outputting the baseband video signal demodulated by the demodulation circuit 16 and an audio output terminal for outputting the baseband audio signal demodulated by the video / audio demodulation circuit 16. The signals output from the video output terminal 17 and the audio output terminal 18 are input to the video / audio signal processing means (not shown) of the VTR. Reference numeral 20 is a video / audio demodulation circuit unit for extracting a baseband video / audio signal, 21 is a burst detection circuit for detecting only a burst signal from the baseband video signal demodulated by the video / audio demodulation circuit 16,
Reference numeral 22 is a frequency correction circuit that performs frequency correction according to the control signal output from the burst detection circuit 3.

The operation of the video frequency characteristic correction apparatus of this embodiment having the above-described structure will be described below.

The video / audio modulation signal input from the antenna 1 is distributed by the distributor 9 to the tuner 14 and the switch circuit 10. One of the distributed video / audio modulated signals is converted into a video / audio intermediate frequency signal by the tuner 14 and input to the video / audio demodulation circuit 16.
The video / audio frequency signal input by the video / audio demodulation circuit 16 is demodulated into a baseband video signal and a baseband audio signal and output from the video output terminal 17 and the audio output terminal 18.

At this time, the baseband video signal output from the video / audio demodulation circuit 16 is the burst detection circuit 2
When it is also input to 1, and becomes more and less than 240 mVp-p, for example, the difference component is detected and the control signal converted into the DC voltage is output to the frequency correction circuit 22 to control the impedance. The frequency correction circuit 22 corrects the video frequency by the control signal and feeds it back to the video / audio demodulation circuit 16. The frequency correction circuit 22 is composed of a varicap for changing the capacitor capacity, for example, and controls the varicap by the DC voltage output from the burst detection circuit 21 to correct the video frequency characteristic.

The other of the signals distributed by the distributor 9 is input to the switch circuit 10. Switch circuit 10
The video / audio modulation signal can be switched between the terminal a side and the terminal b side by a control signal input from the switching control terminal 19. When connected to the terminal a side, the output of the distributor 9 is output to the antenna output terminal 2. When connected to the terminal b side, the video signal and the audio signal input to the RF modulator 11 are converted into modulated signals and output from the antenna output terminal 2.

As described above, in this embodiment, the impedance can be controlled by providing the burst detection circuit and the frequency correction circuit for correcting the video frequency, so that a significantly improved image quality can be obtained.

[0015]

As described above, according to the present invention, the difference between the basic channel and the image between the channels can be reduced by correcting the basic channel and the image frequency characteristic between the channels by the burst detection circuit. Therefore, it is possible to realize a video frequency characteristic correction device capable of suppressing the fluctuation of the image quality and significantly improving the image quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a video frequency characteristic correction device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional video frequency characteristic correction device.

[Explanation of symbols]

 1 antenna input terminal 2 antenna output terminal 9 distributor 10 switch circuit 16 video / audio demodulation circuit 21 burst detection circuit 22 frequency correction circuit

Claims (1)

[Claims] 1. A video frequency characteristic correction device incorporated in a video tape recorder used by connecting to a television receiver, the antenna input terminal for inputting a television signal received by an antenna, and the antenna input terminal. A distributor for distributing the television signal input from the distributor, a switch circuit for switching and outputting one of the output signals of the distributor and the input signal from the recording / reproducing means of the video tape recorder, and the distributor of the distributor. A burst detection circuit that includes a video / audio demodulation circuit that demodulates the other output signal into a video and audio signal, detects a burst signal in the video signal output from the video / audio demodulation circuit, and outputs a control signal, and the burst The frequency is corrected by the control signal output from the detection circuit and is fed back to the video / audio demodulation circuit. A video frequency characteristic correction device, comprising: a wave number correction circuit.