JPS63276388A - Video signal recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the waveform reproducibility of a video signal attended with recording and reproduction by constituting a pre-emphasis circuit so that the amount of emphasis is decreased when the crest value of an input video signal is high. CONSTITUTION:A video signal from an input terminal 1 is fed to a recording/ reproducing head 7 via a buffer 2, a nonlinear emphasis circuit 3, a white clip circuit 4, a frequency modulator 5 and a recording amplifier 6 and recorded on a recording medium 6. A emphasis coefficient is changed for the nonlinear emphasis circuit 3 in response to the level of the video signal so that the level of the emphasized video signal does not exceed the clip level set by the white clip circuit 4. The video signal reproduced by the recording and reproducing head 7 is outputted via a reproducing amplifier 9, a FM demodulator 10, a nonlinear deemphasis circuit 11 and an output amplifier 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video signal recording and reproducing apparatus that records and reproduces video signals using an FM modulation method.

[Conventional technology]

Conventionally, in video signal recording and reproducing devices such as video tape recorders, a method of recording and reproducing video signals by FM modulation has been generally adopted, but in order to improve the S/N degradation of high frequency components in the FM modulation method A pre-emphasis circuit is provided on the recording side to emphasize the high-frequency components of the video signal, and a de-emphasis circuit is provided on the playback side to restore the waveform of the video signal resulting from the pre-en and 7-assist to its original waveform. There is. Also, when pre-emphasizing and FM modulating the video signal in this way, there will be parts where the level of the video signal is too high, and overmodulation will occur in these parts, so there is a gap between the pre-emphasis circuit and the FM modulator. A white clip circuit is provided to cut the level of the video signal higher than the clip level set here to prevent overmodulation.

Note that in the VH8 standard, the time constant iT of the pre-emphasis circuit is 1.3 μsec for the luminance signal.

The emphasis amount X is defined as 4.0, and the clip level of the white clip circuit is defined as 180%.

[Problem that the invention seeks to solve]

By the way, according to the above-mentioned conventional technology, since the amount of emphasis of the pre-emphasis circuit is fixed, the amount of emphasis shown in FIG.
When the video signal with the waveform shown in A) is pre-emphasized, it becomes the waveform shown in FIG. 5(8).
At the high level shown in Figure (A)), part of the pre-emphasized video signal is cut off beyond the clip level Ec set in the white clip circuit as shown in Figure 5 (C). During playback, when de-emphasis is performed by the de-emphasis circuit, the high-frequency components of the video signal are lost (the area surrounded by wavy lines) and the original waveform is lost, as shown in Figure 5 (D). There was a problem that it could not be restored.

SUMMARY OF THE INVENTION An object of the present invention is to provide a video signal recording and reproducing device that solves these problems, improves waveform reproducibility of video signals during recording and reproducing, and significantly improves image quality. .

[Means for solving problems]

In order to achieve the above object, the present invention changes the amount of emphasis of a pre-emphasis circuit depending on the level of a video signal to be recorded.

[Effect]

The pre-emphasis circuit detects the level of the video signal and reduces the amount of emphasis when the level is high.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a video signal recording and reproducing apparatus according to the present invention, in which 1 is an input terminal, 2 is a buffer, 3 is a non-linear emphasis circuit, 4 is a white clip circuit, and 5 is an FM modulation circuit. 6 is a recording amplifier, 7 is a recording/playback head, 8 is a recording medium, 9 is a playback amplifier, 10
11 is a nonlinear de-emphasis circuit, 12 is an output amplifier, and 16 is an output terminal.

In the figure, a video signal input to an input terminal 1 is supplied to a non-linear emphasis circuit 3 and emphasized. This emphasized video signal is cut off at a predetermined level or higher by a white clip circuit 4, and is supplied to an FM modulator 5 for FM modulation. This white clip circuit 4 can prevent overmodulation in the FM modulator 5. F output from the FM modulator 5
After the M video signal is amplified by a recording amplifier 6, it is supplied to a recording/reproducing head 7 and recorded on a recording medium 8.

F reproduced from the recording medium 8 by the recording/reproducing head 7
The M video signal is amplified by a reproduction amplifier 9 and then demodulated by an FM demodulator 10. The video signal output from the FM demodulator 10 is de-emphasized by a non-linear de-emphasis circuit 11, amplified by an output amplifier 12, and output from an output terminal 13.

In such a configuration, the nonlinear pre-emphasis circuit 3 either keeps the time constant T constant according to the standard or changes the emphasis coefficient X according to the level of the video signal, so that the level of the emphasized video signal is adjusted by the white flip circuit 4. The set clip level is not exceeded.

FIG. 2 is a circuit diagram showing a specific example of the nonlinear emphasis circuit 6 having such characteristics.

In the figure, a video signal from a buffer 2 is supplied to the base of a PNP transistor Tr via a clamping capacitor C. A resistor R1 is connected between the emitter of the transistor Tr and the power supply terminal, and a resistor RB is connected between the emitter and the ground terminal.
are connected to each other. Further, the cathode of a diode D+ is connected to the collector of this transistor Tr, and the anode of this diode Dl is connected to the collector of a capacitor C.
I is connected to the power supply terminal via a resistor B2, and the other is connected to a power supply terminal via a resistor &. Further, the collector of the transistor 'I'r is grounded via a load resistor R3, and an emphasized video signal is obtained from this load resistor R3.

In such a non-linear emphasis circuit, the time constant is determined by the resistor R1 and the capacitor C1, and is set to a standard value. Further, the emphasis coefficient X is determined by I Rz+Dr, where k is the forward impedance of the diode Dl. The resistors RA and Ra are bias resistors for non-linear emphasis, and the forward impedance meter is DC controlled by these resistors in accordance with the peak value of the video signal. As a result, the level of the emphasized video signal is set to the clip set in the white clip circuit 4 (FIG. 1) as shown in FIG. 41d (B) for the peak value of the video signal shown in FIG. 4cA). Emphasis coefficient X is changed so as not to exceed level Ec. In this case, the emphasis coefficient X may be changed continuously or in steps with respect to the peak value of the video signal.

FIG. 3 is a circuit diagram showing an example of the nonlinear emphasis circuit 11 in FIG. 1.

In the same figure, the video signal demodulated by the FM demodulator 10 (FIG. 1) is passed through a clamping capacitor C' to an NP
Supplied to the base of the N-type transistor field. The collector of this transistor is connected to the power supply terminal, and the emitter is grounded through the load resistor R (and also connected to the resistance product).The other end of this resistor Rf is grounded through the resistor R4. and is also connected to the cathode of diode D (.The anode of this diode Dr is connected to the power supply terminal via resistor RA on the one hand,
On the other hand, the capacitor Cr1 is grounded via the resistor b. The video signal obtained at the load resistor R( is de-emphasized and output via the resistor R().

This non-linear de-emphasis circuit has the opposite characteristics to the non-linear de-emphasis circuit shown in Figure 2.
When the video signal with the waveform shown in FIG. 4 (03) is input, the video signal with the original waveform is obtained as shown in 411(A).

〔Effect of the invention〕

As explained above, according to the present invention, even if the level of the high-frequency component of the video signal increases due to pre-emphasis, the part for restoring the original waveform is not cut by the white clip circuit, and the signal remains unchanged. The video signal is restored to its original waveform and the image quality is greatly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the video signal recording/reproducing device according to the present invention, FIG. 2 is a circuit diagram showing a specific example of the nonlinear emphasis circuit in FIG. 1, and FIG. 6 is a block diagram showing a specific example of the nonlinear emphasis circuit in FIG. FIG. 4 is a circuit diagram showing an example of a de-emphasis circuit; FIG. 4 is a waveform diagram showing emphasis and white clipping operations in FIG. 1; FIG. 5 is a waveform chart showing emphasis and white clipping operations in the prior art. 3... Nonlinear emphasis circuit, 4... White clip circuit, 5... FM modulation circuit, 10... F
M circuit, 11...Nonlinear de-emphasis circuit Patent attorney Katsuo Ogawa, Figure 1, Figure 2, Figure 3

Claims (1)

[Claims] 1. After pre-emphasizing the input video signal with the pre-emphasis circuit and processing it with the white clip circuit,
In a video signal recording and reproducing apparatus which performs FM modulation for recording, FM demodulates and de-emphasis a reproduced video signal, the pre-emphasis circuit is configured to control the amount of emphasis when the wave height of the input video signal is at a high level. A video signal recording and reproducing device characterized in that the video signal recording and reproducing device is configured such that the video signal decreases.