KR930001329Y1 - Line noise cancelling circuit of vtr - Google Patents

Abstract

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Description

Line Noise Canceling Circuit Using Glass Delay Line

1 is a conventional circuit diagram.

2 is a circuit diagram according to the present invention.

3 is a partial waveform diagram according to the present invention.

4 is a line noise cancel block diagram according to the present invention.

* Explanation of symbols for main parts of the drawings

10: automatic gain control unit 20: dropout detection unit

30: glass delay unit 40, 60: first and second demodulator

50,70: 1, 2 DM wave 80: line noise cancel

The present invention relates to a line noise canceller circuit during recording and playback using a video tape recorder (VTR), and more particularly to a circuit for noise processing using a glass delay line. It is about.

In general, a glass delay line or a charge coupled device (CCD) is used to compensate for a drop out signal generated from a tape damage part when playing a video tape.

A circuit 1a using the conventional glass delay line and a circuit 1b using the conventional CCD are shown in FIG.

The CCD is capable of performing a line noise cancel function at the same time as a drop out compensation function, but not with a glass delay line.

However, when CCD is used, a clock frequency of a high frequency (7-15KHZ) must be used, which causes a problem that clock noise is severe and expensive.

Accordingly, an object of the present invention is to provide a circuit capable of performing line noise canceling operation while compensating for dropout using a glass delay line when playing a videotape.

Hereinafter, the present invention will be described in detail with reference to the drawings.

2 is a circuit diagram according to the present invention, an automatic gain control unit 10 for outputting the same gain when a reproduction signal is input, a drop out detection unit 20 for detecting the drop out of the output signal of the automatic gain control unit 10, When the drop out is detected by the drop out detection unit 20, the glass delay unit 30 delaying the output signal of the automatic gain control unit 10 by 1 H and the drop out detection unit 20 detect the drop out. If not, the first demodulator 40 for demodulating the output signal of the automatic gain control unit 10, the first DMP unit 50 for deemphasing the demodulation signal of the first demodulator 40, and the glass delay unit. A second demodulator 60 for demodulating the output signal of 30, a second DM wave unit 70 for deemphasing the demodulation signal of the second demodulator 60, and the first and second DM wave units 50; , 70) input signal to reduce the line noise by a predetermined multiple to output the video signal Constitute a line noise canceller la 80. The

3 is a partial waveform diagram according to the present invention.

4 is a block diagram of a line noise canceler according to the present invention.

Based on the above configuration, the present invention will be described in detail with reference to FIGS.

First, a reproduction signal such as the waveform of FIG. 3 (a) read from the tape during VTR reproduction is input to the automatic gain control section 10, and always outputs a signal having the same gain if it is within the automatic gain control range.

The output signal of the automatic gain control unit 10 is input to the dropout detection unit 20 to detect a dropout. When the dropout is not detected by the dropout detection unit 20, the dropout detection unit 20 switches to a normal terminal NOR and inputs an output signal of the automatic gain control unit 10 to the first demodulator 40. The first demodulator 40 demodulates the input signal, deempasis through the first DM wave unit 50, and inputs it to the line noise canceler 80. In addition, when a dropout is detected by the dropout detection unit 20, the dropout terminal D0 is switched to input the output signal of the automatic gain control unit 10 to the glass delay unit 30.

The glass delay unit 30 delays the input signal by 1H and inputs a signal such as a waveform of FIG. 3B to the second demodulator 60. The second demodulator 60 demodulates the output signal of the auto gain control unit 10 delayed by 1H, deemphases through the second DMP unit 70, and inputs the line signal to the noise canceler 80. Comparing the two signals input to the line noise canceller 80, both signals are demodulated together to have a horizontal synchronization signal, but the two signals have a 1H delay relationship. By reducing the noise, the line noise cancel function can be performed. 4 illustrates the line noise canceller in detail. First, Sin is a reproduction input signal, Nm is 1H delayed noise, NM is noise input together with the reproduction input signal, Is the absolute noise value. The reproduction input signal picked up from the tape (Sin + NM) always contains noise. The noise is reduced through a line noise canceller. First, the reproduction input signal Sin + NM is input to the first and second subtractors, and the reproduction input signal is delayed through the 1H delay unit so that the delayed signal Sin + Nm is input to the first subtractor. The 1H delay unit is the glass delay unit 30 of the present invention. Two signals inputted to the first subtractor are subtracted to extract only noise, thereby producing Equation (1) below, in which noise (NM + Nm) is a noise (N) as shown in FIG. 3 (c) through a limiter.

Noise (N) of the formula (1) is input to the second subtractor after readjustment to an appropriate level with the variable resistor (VR). The second subtractor subtracts the inputted reproduction input signal Sin + NM and the noise N to obtain a final output signal Sout as shown in (2).

The final output signal Sout of Equation (2) is the same as the waveform of FIG. 3 (d), and the original reproduction input signal Sin does not change but the noise level is higher than that of the reproduction input signal Sin. Reduced by 2x

The noise of the reproduction signal generated on the tape format of the VTR as described above is reduced by a predetermined fold by canceling the line noise canceling operation while compensating for the dropout using the glass delay line. There is an advantage that the quality of the product is improved screen state.

Claims (1)

In the line noise cancel circuit of a video tape recorder having an automatic gain control unit (10) and a dropout detection unit (20), if there is a dropout by the detection of the dropout detection unit (20), the automatic gain control unit ( 10) the glass delay unit 30 which delays the reproduction signal mixed with noise by 1H, and the reproduction signal mixed with noise from the automatic gain control unit 10 when there is a dropout by the detection of the dropout detection unit 20. A first demodulator 40 for demodulating the first demodulator, a first DM wave unit 50 for deemphasing the demodulation signal of the first demodulator 40, and a second demodulation output signal of the glass delay unit 30. A line noise by inputting a demodulator 60, a second DM wave unit 70 for deemphasing the demodulation signal of the second demodulator 60, and output signals of the first and second DM wave units 50 and 70; Is a line noise canceller that outputs a video signal by reducing A line noise canceling circuit using a glass delay line, characterized in that consisting of 0).