JPS6013600B2 - Color video signal reproducing device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a color video signal reproducing device.

When a video signal is reproduced from a magnetic tape, the reproduced video signal is subject to fluctuations depending on the surface condition of the tape.

In the case of a color video signal, the luminance signal is angularly modulated, e.g. FM
There is no problem because it is modulated, but... There is a problem with the carrier color signal. For this reason, playback devices generally use ACC.
A circuit is provided to detect the level of the burst signal in the carrier color signal, and control the level of the carrier color signal with the detection signal,
Level fluctuations in the carrier color signal are corrected. However, in the ACC circuit, since the level of the burst signal is relatively small and the burst signal only exists for a short time, it is difficult to sufficiently compensate for level fluctuations when the S/N of the burst signal is poor. The disadvantage is that it cannot be done.

Furthermore, when the level changes in a cycle that is shorter than the horizontal cycle, the level of the burst signal and the level of the carrier color signal do not correspond, so correction is impossible in principle. In view of these points, the present invention is designed to reliably correct level fluctuations in a carrier color signal.

FIG. 1 shows an example of the present invention, in which a reproduced color video signal obtained by a head 1 is supplied to a high-pass filter 11 through a reproduction amplifier 2 and a gain control circuit 31.
The M-modulated luminance signal is taken out, and this is sent to limiter 1.
2 to a demodulator 13 for demodulation, and the demodulated luminance signal is supplied to a synthesizer 3 via a low-pass filter 14.

On the other hand, the color video signal from the gain control circuit 31 is supplied to the low-pass filter 21 to take out the carrier color signal that has been low-pass converted, and this is supplied to the frequency converter 23 through the ACC circuit 22 and converted to the original frequency. The converted carrier color signal is supplied to the synthesizer 3 through the bandpass filter 24, and the original color video signal is taken out at the output terminal 4. And in this example, high pass filter 1
The FM-modulated luminance signal from 1 is supplied to an amplitude detection circuit 32 for amplitude detection, and the detected signal is supplied to a gain control circuit 31 through a low-pass filter 33 to control its gain.

That is, the level of the reproduced color video signal, and hence the level of the reduced-converted carrier color signal, is controlled in a negative feedback manner according to the level of the FM-modulated luminance signal in the reproduced color video signal. Assuming that the cause of the level fluctuation is the spacing loss during reproduction, the level 8Y of the FM-modulated luminance signal in the reproduced color video signal and the level Ec of the low-pass converted carrier color signal are EY = KYeXp (- 1 )．
・…．・．． ...EC=KC ground (-sky 1).・・・．・・・．・
・[Represented by 21.

However, KY and Kc are constants, 1 is the amount of spacing, and input Y
is the recording wavelength of the luminance signal, and c is the recording wavelength of the carrier color signal. In Equations 1) and 21, if we take the logarithms of both sides, we get Wakiko KY-Roh.・・・．・・・．・Side armpit=InkC-should be 1. ．．・．． ．．・．． ．．・[4] From the glue formula, 1 = Gotsukuda Y - 1 HiY) ....・．． ．．・・【
5}.

Substituting this '5} expression into the ■ expression, side=Ink. - etc.
Meng (1 ship Y - 1 valence Y) = 1 female C + Sa (1 night Y - IMY) = sail.

(Bale)... ...be on the side.

Therefore, E.

;KC (Noboru) Gi ・-・-・---There is a relationship between them. Therefore, the amplitude detection circuit 32 detects the level EY of the FM-modulated luminance signal, and the gain control circuit 3
If the loop gain of 1 is set to a relatively low and moderate value, and the gain is controlled so that the EY holes are multiplied as shown in Figure 7, the level of the carrier color signal will be
EYEC'=EC・EYEC=K.

Agriculture. EYsuCeeY=KC・KYeeC

......[81] Since ^Y and ^c are constant regardless of the subbasing amount 1, Ec' becomes a constant value, and there is no level fluctuation due to subbasing loss of the carrier color signal.

Although subbasing loss also occurs during recording, level fluctuations due to subbasing loss during recording can also be corrected by appropriate gain control characteristics.

Although some level fluctuations are due to tracking fluctuations, level fluctuations due to tracking fluctuations appear exactly the same in the luminance signal and the carrier color signal. The level fluctuation due to this tracking fluctuation has a large period. Therefore, by using a low-pass filter 33 with characteristics such that the loop gain becomes large at low frequencies, level fluctuations due to tracking fluctuations can also be corrected. If the luminance signal subjected to FM modulation before the amplitude detection circuit 32 has appropriate frequency characteristics, it is possible to correct the level fluctuation of the carrier color signal due to the carrier of the luminance signal.

In addition, in reproducing equipment using two rotating magnetic heads, correction may be performed for each output of each head.

Since the level of the luminance signal in the reproduced color video signal is sufficiently higher than the level of the carrier color signal, the color video signal from the gain control circuit 31 is directly supplied to the amplitude detection circuit 32 as shown in the example of FIG. Alternatively, amplitude detection may be performed.

In this case, as in the example of FIG.
It is also possible to supply the reproduced color video signal before this to the high-pass filter 11 to extract the luminance signal.

As the compensation circuit, a non-road circuit having limiter characteristics can also be used.

FIG. 4 shows an example of this case, in which a non-linear circuit 41 is inserted in place of the gain control circuit 31 in the example in FIG. 2. In this case as well, as in the example of FIG.
It is also possible to supply the reproduced color video signal before 1 to the high-pass filter 11 and extract the luminance signal.

FIG. 6 shows an example of a non-linear circuit 41, in which a parallel circuit of two diodes 53 and 54 in opposite directions and a resistor 61 are connected between the collectors of transistors 51 and 52 forming a differential amplifier. It is configured as a soft limiter.

Note that 55 is a transistor forming a constant current source, 56 is an input device, 57 is an emitter follower transistor for taking out an output, and 58 is an output end. In this circuit, by adjusting the resistor 61 and the resistor 62 on the emitter side of the transistors 51 and 52, appropriate nonlinear characteristics can be obtained as shown by the solid line in FIG.

Even when using such a non-traffic line circuit 41, it is possible to correct level fluctuations in the carrier color signal in the same way as when using a gain control circuit.

That is, for example, when a reproduced color video signal is passed through the non-linear circuit 41 having the characteristics shown by the solid line in FIG. In this case, the equivalent gain is approximately 0.5, as shown by the broken line ■. In this way, the nonlinear circuit 41 can be regarded as a circuit whose equivalent gain changes depending on the input amplitude, if distortion is ignored.

When the luminance signal on which the carrier color signal is superimposed is input to the nonlinear circuit 41, the gain changes depending on the luminance signal, and as a result, the output level of the carrier color signal is controlled.

As described above, according to the present invention, since the angle-modulated luminance signal is used to correct the level fluctuation of the carrier color signal, it is possible to reliably correct the level fluctuation of the short period. I can do it.

[Brief explanation of the drawing]

1 to 5 are system diagrams of an example of a reproducing device according to the present invention, FIG. 6 is a connection diagram of a specific example of a nonlinear circuit, and FIGS. 7 and 8 are diagrams for explaining the present invention. It is. 31 is a gain control circuit, and 41 is a nonlinear circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. A device for reproducing a composite signal in which an angle-modulated luminance signal and a low-frequency-converted carrier color signal are multiplexed from a magnetic recording medium, which separates the luminance signal from the composite signal and passes it through a limiter circuit. Then, together with a circuit for frequency demodulating this signal, at least the composite signal is passed through a nonlinear circuit having limiter characteristics, and then a low frequency conversion carrier color signal is separated, and this separated color signal is frequency converted to a high frequency. A color video signal reproducing device that includes a circuit to compensate for level fluctuations in a carrier color signal due to spacing loss during reproduction.