JPS6021520B2 - Color signal processing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color signal processing circuit in equipment using a low carrier wave recording/reproducing method, such as a color VTR.

In color VTRs, etc., the carrier color signal of the color video signal to be recorded is generally converted to low frequency, its bursts are emphasized and recorded, and the frequency is converted again for playback, and the level of the bursts is suppressed to restore the original. The method is such that the signal is returned to the carrier color signal (referred to as carrier color signal conversion or burst level conversion method). As a color signal processing circuit of this type, for example, one having a configuration as shown in FIG. 1 is known.

In this figure, 1 is a recording video signal input terminal, 2 is an Obishiro pass filter, 3 is a burst level emphasis circuit, 4 is a playback signal input terminal, 5 is a low pass filter, and 6 is for recording/playback control. switch circuit, 7 is an automatic color signal gain control circuit (A
8 is a frequency converter, 9 is a peak detector for ACC, 10 is a low-pass filter, 11 is a color signal recording output terminal, 12 is a band-pass filter, 13 is a burst level suppression circuit, and 14 is a color signal reproduction output terminal.

The operation of this circuit is as follows. First, when recording,
The switch circuit 6 is switched to the a side, and the input terminal 1 is supplied with a color video signal.

When a color video signal is supplied to terminal 1, only the carrier color signal is extracted from this signal by bandpass filter 2, and when the color signal information level is at its maximum, this signal becomes as shown in Figure 2A. It has a waveform (C in this figure)
is a burst, and d is a color information component).

Next, this signal is subjected to a burst emphasis circuit 3 that emphasizes only the burst component, resulting in a signal with a waveform as shown in FIG. In the low-pass filter 10, only the low-pass converted carrier color signal is taken out to the terminal 11 and recorded. Further, during reproduction, a reproduction signal from the recording/reproducing device is supplied to the input terminal 4, and the switch circuit 6 is switched to the b side.

The carrier color signal that has been low-pass converted and extracted from the signal supplied to the terminal 4 by the low-pass filter 5 is supplied from the switch circuit 6 to the frequency converter 8 via the ACC circuit 7. has the same waveform as the signal appearing at the output terminal 11 during recording, as shown in FIG. 2B.

The signal converted from the low frequency range to the original frequency by the frequency converter 8 has unnecessary frequency components removed by the bandpass filter 12, and is then applied to the burst level suppression circuit 13, which suppresses only the burst level and restores the original frequency. This becomes a carrier color signal (FIG. 2A) and is output to the output terminal 14. Also,
In both recording and reproduction, the signal obtained from the output of the frequency converter 8 is supplied to the peak detector 9, and the output is applied to the ACC circuit 7 for ACC operation, thereby converting the carrier color signal including bursts. The gain is automatically controlled according to the overall peak level so that the peak level becomes a constant signal.

However, in a circuit with such a configuration, processes such as emphasis and suppression of bursts in the carrier color signal are performed in separate circuits during recording and during playback, resulting in a complex configuration. It had the disadvantage of becoming

SUMMARY OF THE INVENTION An object of the present invention is to provide a color signal processing circuit that eliminates the drawbacks of the prior art described above, has a simple configuration, and can obtain a carrier color signal with a stable burst level.

In order to achieve this object, the present invention is characterized in that a circuit for emphasizing and suppressing bursts is provided, which is shared during recording and reproduction, and the output of this circuit is used to operate the ACC.

Hereinafter, the present invention will be explained with reference to the drawings. FIG. 3 shows an embodiment of the present invention, which differs from the circuit shown in FIG. 1 in that the burst emphasis circuit 3 used during recording and the burst level suppression circuit 13 used during playback are removed; Instead, a burst processing circuit 15 having the configuration shown in FIG. 4 is provided, and a switch circuit 16 is inserted to share this circuit 15 for recording and reproduction.
The input is given from the burst emphasis output h of this processing circuit 15.

Since the other parts are the same as those shown in FIG. 1, detailed explanation will be omitted. Next, the operation of this embodiment will be explained.

First, during recording, as in the case of FIG. 1, the switch circuit 6 is closed to the a side, and at the same time the switch circuit 16 is also closed to the e side, and a video signal to be recorded is supplied to the input terminal 1.

From this video signal, only the carrier color signal is extracted by the Obishiro filter 2, and is applied to the frequency converter 8 via the switch circuit 6 and the ACC circuit 7, where it is converted into a low frequency signal. Only the low-pass converted components of the converted carrier color signal are taken out by the low-pass filter 10, and are supplied to the input g of the burst processing circuit 15 via the switch circuit 16. The waveform of the low frequency conversion carrier color signal coupled to this input g is as shown in FIG. 2A, and its level relationship remains the same as that of the signal at input terminal 1.

Now, this burst processing circuit 15 has a configuration as shown in FIG.
A resistor R is connected to the output i so that the signal applied to the output i is divided and taken out as outputs h and i, and a burst gate switch circuit 18 that is periodically closed during the burst period is connected to the output i.

The voltage is divided by the series resistor Rc. And these resistances RB, Rc
, Ro, so that when the switch circuit 18 is closed, the signal appearing at the output h' is more emphasized than when the switch circuit 18 is open; The signal appearing at i can be operated to be suppressed by approximately B.

Therefore, the signal (low-pass converted carrier color signal) supplied to the input g of the burst processing circuit 15 from the low-pass filter 10 via the switch circuit 16 is
Since the switch circuit 18 opens and closes periodically only during the burst period of the carrier color signal, the signal shown in FIG. An output h' appears from the collector of the transistor 17 as an emphasized signal, and is supplied from the output terminal 11 to the recording/reproducing device.

At the same time, the carrier color signal having the waveform shown in FIG. 2B from this output h is supplied to the peak detector 9, and its output is ACC.
is added to circuit 7 to perform ACC operation, and output terminal 1
The peak level of the signal appearing at 1 is automatically held at a constant level.

Next, during playback, the switch circuits 6 and 16 are closed to the b side and f side, respectively, and the playback signal from the recording and playback device, that is, the carrier color signal that has been low-frequency converted, is supplied to the input terminal 4. .

The low-pass converted carrier color signal from which unnecessary components have been removed by the low-pass filter 5 is supplied to the frequency converter 8 through the switch circuit 6 and the ACC circuit 7, where it is frequency-converted to the original frequency. Only the necessary frequency components are extracted by the bandpass filter 12 and supplied to the input g of the burst processing circuit 15 via the switch circuit 16.

The level relationship of the signals at this time is the same as the output signal during recording, as shown in FIG. 2B. In the burst processing circuit 15, as in recording, the burst gate switch circuit 18 is periodically opened and closed and is closed only during the burst period of the carrier color signal, so that the carrier color signal ( The waveform of FIG. 2B) is a level-related signal like the waveform of FIG. 2A, in which only the burst is extracted from the emitter of transistor 7 and is suppressed, that is, the original carrier color signal. The same signal is sent to output terminal 14
will be obtained.

At this time, in the output h of the burst processing circuit 15, only the burst is reduced and the B-emphasized signal is simultaneously generated, which has a level relationship as shown in FIG. 2C. This is because the signal with the waveform shown in FIG. 2B is supplied to the input g, and only the burst is emphasized, so that the signal shown in FIG. 2C is obtained at the output h. Then, the signal having the waveform shown in FIG.
will work.

As is clear from this signal, that is, the signal shown in FIG. Sufficient detection output can be obtained.

Therefore, a control signal of a sufficient value is applied to the ACC circuit 7 from the peak detector 9 for a predetermined period depending on the burst level, almost independently of changes in the level of the erotic grain, so that the ACC operation is always performed in a sufficient state. Therefore, a carrier color signal whose burst level is automatically kept constant can be obtained at the output terminal 14. As explained above,
According to the present invention, there is no need to provide separate circuits for burst emphasis and burst suppression, which simplifies the configuration, ensures sufficient ACC operation during reproduction, and improves the color information level in the carrier color signal. It is possible to obtain a signal with a stable burst level without being affected by fluctuations in the signal.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a color signal processing circuit in a conventional low-carrier type recording/reproducing device, Fig. 2 is a waveform diagram showing the level relationship between the color information of the carrier color signal and the burst, and Fig. 3 is a waveform diagram showing the level relationship between the color information of the carrier color signal and the burst. FIG. 4 is a block diagram of a color signal processing circuit according to an embodiment of the present invention. FIG. 4 is a wiring diagram showing a specific example of the burst processing circuit shown in FIG. 3. 2...Obijo passing filter, 5...Low pass filter, 7...ACC circuit, 8...
Frequency converter, 9...Peak detector, 10...
...Low pass filter evening, 12...Obijo passing filter evening, 15... ...Burst processing circuit. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In a color signal processing circuit using carrier color signal conversion and burst level conversion methods, there is a circuit that simultaneously forms a signal with an enhanced burst level and a signal with a suppressed burst level, and a signal with an enhanced burst level is input from this circuit. 1. A color signal processing circuit comprising an automatic color signal gain control circuit.