JPS5946046B2 - Recording/playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pre-emphasis circuit used in a magnetic recording/reproducing device that converts a video signal into an angle modulation signal such as an FM signal and records the same.

A video tape recorder (hereinafter referred to as VTR) is a typical conventional recording and reproducing device, and in the pre-emphasis circuit type used in this, when the pre-emphasis amount is increased, the It is greatly clipped by the bright clip circuit,
Although the S/N of the reproduced image quality was improved, there was a drawback that the outline became blurred. Hereinafter, conventional problems will be explained using FIGS. 1 and 2.

FIG. 1 shows an example of a pre-emphasis circuit and a white peak clipping circuit of a VTR, and FIG. 2 shows waveforms of various parts of FIG. In FIG. 1, 1 is a pre-emphasis transistor, and 2 is a white peak clip diode.

Let the resistance values of the resistors R1 and R2 be R1 and R2, and the capacitance value of the capacitor Cl be Cl. The video signal A having the waveform shown in FIG. 2A (in the case of a home VTR, the band is limited to about 3 MH2) applied to the input terminal 8 of the pre-emphasis circuit has a pre-emphasis amount determined by R2/R1, C.
The high frequency band is emphasized with a time constant determined by l(R1+R2), and an overshoot waveform as shown in FIG. 2B is obtained at the output terminal 9.

Here, the overshoot on the white side is normally clipped at a level of 150 to 200%, assuming that the video signal is 100%. The reason for clipping is that if it is not clipped, the FM frequency will become too high in the overshoot area, causing the output level to drop in the playback circuit, resulting in a so-called inversion phenomenon (black pulse noise occurs at the contour where black changes to white).
This is because this causes a significant deterioration in the reproduced image quality. Therefore, white peak clipping must be performed, and if the amount of pre-emphasis is increased in an attempt to improve the S/N ratio, most of the overshoot will be clipped and the outline of the reproduced image will deteriorate.

Although the above-mentioned inversion phenomenon is eliminated by white peak clipping, another drawback arises in that the outline becomes blurred. Of course, this edge blurring causes less deterioration in image quality than the inversion phenomenon. The present invention eliminates the above-mentioned drawbacks of the prior art and provides a new type of pre-emphasis circuit that does not cause contour deterioration of reproduced images even when the amount of pre-emphasis is increased.

A pre-emphasis circuit according to the present invention includes a circuit that delays an input video signal, a low frequency wave circuit that passes a low frequency component of the input video signal, an output signal of the delay circuit, and an output signal of the low frequency wave circuit. and a subtraction circuit that outputs a difference signal between the two.

FIG. 3 shows a pre-emphasis circuit and a white peak clip circuit showing one embodiment of the present invention, and FIG. 4 shows waveforms of various parts of FIG. 3. In FIG. 3, 3 is a delay circuit, 4 is a low-frequency wave generator, and 5 is a subtracter consisting of a differential amplifier circuit, and these circuits constitute a pre-emphasis circuit. When the video signal shown in FIG. 4A is applied to the input terminal 8 of the pre-emphasis circuit, part of it passes through the delay circuit 3 and becomes a waveform C delayed by τ, and part of the input signal passes through the low-frequency wave generator 4. A waveform like ゜D is obtained.

These two signals C and D are connected to a differential amplification transistor Ql,
When amplified by Q2, a waveform like waveform E with print and overshoot is obtained at the collector of Q. Here, the printed overshoot exceeding the clip level is caused by diode 2 of the white peak clip circuit.
The signal is clipped and applied to the next stage FM modulator.
In this circuit, not only overshoot but also printate is added in this way, so even if the white peak side is clipped and the contour component decreases, the contour will be corrected by the printate or overshoot component immediately before or after it. Emphasis is placed. Here, the pre-emphasis amount is determined by the resistance value ratio R5/R4 of the resistors R5 and R4, and the pre-emphasis time constant is approximately determined by C2R3, and the delay time τ of the delay circuit 3 needs to be selected to a value close to the pre-emphasis time constant. In the case of a household TR, the pre-emphasis time constant C2R3 is approximately 0.6 to 1.0 μS, and the delay circuit 3 also requires 0.6 to 1.0 μS.

On the other hand, in home VTRs, as is well known, a color image signal is separated into a video signal and a color signal, each processed separately and then recorded. and,
The recording low frequency wave generator used to separate this video signal limits the band of the input video signal to approximately 3 MHz, and also to match the time relationship between the video signal and color signal on the tape. It has the function of delaying the video signal by .0μS. Therefore, it is possible to use this recording low-frequency wave generator or a part thereof in the delay circuit 3 used in the pre-emphasis circuit of the present invention.

That is, since the recording low-frequency wave generator is placed before the pre-emphasis circuit, the input of the low-frequency wave generator 4 shown in Fig. 3 is connected to the input terminal of this recording low-frequency wave generator or in the middle thereof. Then, the delay circuit 3 can be omitted since it can also be used as a delay means for applying printate and overshoot. In this case, the cost increase over the conventional pre-emphasis circuit can be extremely reduced. FIG. 5 shows a de-emphasis circuit used in the reproduction system for FIG. 3. The input terminal 10 in Fig. 5 has an FM
The output signal of the demodulator is applied, and a video signal is obtained at the output terminal 11 in FIG.

Delay time of delay circuit 6 that determines de-emphasis characteristics,
Time constant C3R6 of low frequency wave generator 7, de-emphasis amount R
8/R7 are τ, C2R3, and C2R3 of the pre-emphasis circuit, respectively.
It is necessary to choose approximately equal to R5/R4.

The delay circuit 6 used in the de-emphasis circuit can also use a low-frequency r wave filter or a part thereof to match the time relationship between the reproduced video signal and the color signal and to remove unnecessary signals from the output of the FM demodulation circuit. .

Even when the pre-emphasis circuit according to the present invention is used in the recording system of a recording/reproducing apparatus, it is not necessarily necessary to use the de-emphasis circuit according to the present invention having the configuration shown in FIG. 5 in the reproduction system, and other configurations may be used. It is clear that the effects of the pre-emphasis circuit according to the present invention can be exhibited even with the de-emphasis circuit of the present invention.

By using the pre-emphasis circuit of the present invention, contour enhancement by printate is added, which compensates for the blurring of the contour due to white peak clipping, making it possible to increase pre-emphasis by approximately 6 dB compared to the conventional method.
Therefore, the S/N of the reproduced image can be improved by about 6 dB.

Although the pre-emphasis circuit of the present invention is more complex than the conventional one, the present invention can be used because the delay circuit used therein can also be used as a low-frequency wave generator or a part of this which originally exists in the VTR. The resulting cost increase is extremely small.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional pre-emphasis circuit and a white peak clip circuit, FIG. 2 is a diagram showing waveforms of each part in FIG. 1, and FIG. 3 is a diagram showing an embodiment of the pre-emphasis circuit of the present invention. FIG. 4 is a diagram showing waveforms at various parts in FIG. 3, and FIG. 5 is a diagram showing an embodiment of the de-emphasis circuit of the present invention. 3...delay circuit, 4...low frequency wave generator,
7... Subtraction circuit.

Claims (1)

[Claims] 1. A circuit for pre-emphasizing the video signal that has passed through the recording low-pass filter in order to match the time relationship between the video signal and the color signal on the recording medium, a clip circuit for limiting the amplitude of the pre-emphasized video signal, and a clip. In an apparatus for converting an output signal of a circuit into an angle modulation signal and recording this angle modulation signal on the same recording medium as a separately processed color signal, the pre-emphasis circuit is combined with a delay means for delaying a video signal and a video signal. A subtraction circuit that outputs a difference signal between the output signal of the delay means and the output signal of the low-pass filter circuit, and a preshoot circuit that outputs a difference signal between the output signal of the delay means and the output signal of the low-pass filter circuit. What is claimed is: 1. A recording/reproducing apparatus characterized in that the recording/reproducing apparatus obtains a video signal with an overshoot added thereto, and utilizes at least a part of the recording low-pass filter as the delay means.