JPH0685574B2 - Signal processing circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit, and more particularly to reduction of waveform deterioration due to clipping in a signal system of a video signal recording / reproducing apparatus.

(Prior Art) FIG. 6 is a block diagram of a conventional luminance signal system of a video signal recording / reproducing apparatus.

As shown in the figure, on the recording side of the luminance signal system, the input luminance signal from the input terminal 1 is automatically adjusted to a predetermined signal level by the AGC 2 and supplied to the non-linear emphasis 4 via the low pass filter (LPF) 3. Together with AGC2
The signal, which is fed back to, and then emphasized in the high frequency range by the non-linear emphasis 4 is further emphasized in the high frequency range by the emphasis system 5, and then applied to the clip 6, where the spike tip that can rise and fall parts of the signal is applied. After being clipped, the signal is FM-modulated by the FM modulator 7, and the band for the low-pass conversion color signal is secured by the high-pass filter (HPF) 8. Then, the recording amplifier 9 adjusts the optimum recording current, and the video is adjusted. Supplied to the head 10, where the magnetic tape 11
Recorded in.

On the reproduction side of the luminance signal system, the reproduction signal reproduced from the magnetic tape 11 by the video head 12 is stored in the preamplifier 13
Is supplied to the high-pass filter (HPF) 14, where the low-pass conversion color signal is removed from the reproduced signal, FM demodulated by the FM demodulator 15, and demodulated by the low-pass filter (LPF) 16. The carrier component of the signal is removed, the high frequency attenuation of the signal is performed by de-emphasis 17, and the high frequency attenuation is further performed by the non-linear de-emphasis 18, and then noise reduction is performed by the noise suppression circuit 19 and reproduced from the output terminal 20. The luminance signal is output.

The configuration described above is for the long time mode.

The configuration in the standard mode is obtained by omitting the non-linear emphasis 4 and the non-linear de-emphasis 18 from the above-mentioned configuration in the long time mode.

The long-time mode is a mode in which recording / reproduction is performed at a speed slower than the recording / reproduction speed in the standard mode, and is, for example, about 1/3 of the speed in the standard mode.

FIG. 7 is a diagram showing an example of the non-linear emphasis characteristic of the non-linear emphasis 4, and FIG. 8 is a diagram showing an example of the emphasis characteristic of the emphasis 5.

FIG. 9 is a diagram showing an input waveform of the clip 6, where FIG. 9A shows the waveform in the standard mode and FIG. 9B shows the waveform in the long time mode.

In the long time mode, the high-frequency part of the output signal of LPF3 is raised with non-linear emphasis 4 as shown in FIG. 7, and the high-frequency part of this signal is further increased with emphasis 5 as shown in FIG. Therefore, in the case of the long time mode, compared to the case of the standard mode in which the high frequency part of the output signal of LPF3 is raised only by emphasis 5,
As the high frequency is emphasized by the non-linear emphasis 4, the whiskers of the waveform after passing through the emphasis 5 become large (portion A shown in FIG. 9B).

Therefore, since there are more signal portions (information) that exceed the clip level of the clip 6 in the long-time mode than in the standard mode, there is a disadvantage that more information is lost due to clipping.

The above-mentioned clip level is the white clip level, but the same applies to signals that exceed the dark clip level, so we will describe the loss of signals that exceed the white clip level below, and regarding signals that exceed the dark clip level. The description of is omitted.

(Problems to be Solved by the Invention) In the above-mentioned clipping of the luminance signal system of the video signal recording / reproducing apparatus, the signal portion (information) lost in the long time mode is clipped and lost than in the standard mode. Because of the large number of signals, the long-time mode has a drawback that a signal necessary for faithfully reproducing a fine pattern is missing in the long-time mode, and a good reproduced image cannot be obtained.

(Means for Solving Problems) The present invention provides a signal processing circuit having the following configuration in order to solve the problems described above. That is, the signal processing circuit of the present invention is a signal processing circuit in a luminance signal system of a video signal recording / reproducing apparatus for recording / reproducing in a standard mode or a long-time mode having a recording / reproducing speed lower than the recording / reproducing speed in this standard mode. On the recording side, the luminance signal to be recorded is supplied to one input terminal of the differential amplifier section, the clip section for suppressing the amplitude of the output signal of the differential amplifier section at a predetermined level, and the clip section. The output signal of the section is output to the non-linear emphasis circuit and the de-emphasis section which supplies the signal to the other input terminal of the differential amplifier section. A first clip circuit for setting a clip level in the standard mode, and the de-emphasis unit that constitutes the first clip circuit A non-linear emphasis circuit that emphasizes high-frequency components according to the signal level of the output signal, an emphasis circuit that further emphasizes high-frequency components of the output signal of this non-linear emphasis circuit, and the amplitude of the output signal of this emphasis circuit to a predetermined level. And a second clip circuit that suppresses the second clip circuit, and the reproduction side is configured to be complementary to the second clip circuit.
Clip compensating circuit for expanding the reproduced signal by the amount of the signal amplitude suppressed by the clipping circuit, and a de-emphasis circuit which is configured complementarily to the emphasis circuit and complementarily attenuates the high frequency component of the output signal of the clip compensating circuit. And configured to be complementary to the non-linear emphasis circuit,
A non-linear de-emphasis circuit that complementarily attenuates a high frequency component according to a signal level of an output signal of the de-emphasis circuit, in a long time mode, on the recording side, the first clipping circuit and The non-linear emphasis circuit, the emphasis circuit,
The second clip circuit is provided, and the reproducing side is provided with the clip compensating circuit, the de-emphasis circuit, and the non-linear de-emphasis circuit. Is configured such that the first clipping circuit and the emphasis circuit are not provided but the non-linear emphasis circuit and the second clipping circuit are provided, and the clip compensation circuit and the nonlinear circuit are provided on the reproducing side. It is a signal processing circuit characterized by being configured so as to intervene through the de-emphasis circuit without passing through the de-emphasis circuit.

(Embodiment) FIG. 1 is a diagram best representing the features of the present invention.

FIG. 2 is a block diagram of an embodiment of the signal processing circuit according to the present invention.

The same components as those described above are designated by the same reference numerals,
The description is omitted.

The signal processing circuit according to the present invention is in the luminance signal system. The recording side of the luminance signal system is AGC2, low-pass filter (LPF)
3, the first clip 21, the non-linear emphasis 4, the emphasis 5, the second clip 22, the FM modulation 7, the high-pass filter (HPF) 8, the recording amplifier 9, the video head 10, and the playback side of the luminance signal system , Video head 12,
Preamplifier 13, high-pass filter (HPF) 14, FM demodulation 1
5, low pass filter (LPF) 16, clip compensation 23, de-emphasis 17, non-linear de-emphasis 18, noise suppression circuit 19.

The configuration described above is for the long time mode.

The configuration in the standard mode is obtained by omitting the second clip 22, the non-linear emphasis 4, the clip compensation 23 and the non-linear de-emphasis 18 from the configuration in the long time mode described above.

The reason why the non-linear emphasis 4 and the second clip 22 can be omitted on the recording side in the standard mode is that the clip amount of the clip 25 constituting the first clip 21 is set to the clip level in the standard mode. This is because the leading edge of the output waveform of the emphasis 5 falls within a predetermined level.

Next, the operation of the signal processing circuit configured as described above will be described.

The input luminance signal from the input terminal 1 is supplied to AGC2, LPF3, the first clip 21, the non-linear emphasis 4, the emphasis 5, the second clip 22, the FM modulation 7, the HPF 8, the recording amplifier 9, and the video head 10. It is recorded on the magnetic tape 11.

The signal reproduced from the magnetic tape 11 is supplied to the video head 12,
Preamplifier 13, HPF14, FM demodulation 15, LPF16, clip compensation
23, de-emphasis 17, non-linear day emphasis
18 and a noise suppression circuit 19 to output from the output terminal 20 as an output luminance signal.

The first clip 21 mentioned above is a differential amplifier 24, a clip
It consists of 25 and 26 de-emphasis.

The + input terminal of the differential amplifier 24 is connected to the output terminal of the LPF3, the output terminal thereof is connected to the input terminal of the clip 25, and the output terminal of the clip 25 is connected to the − input terminal of the differential amplifier 24 via the de-emphasis 26. It is connected. Differential amplifier 24
-Input terminal and output terminal of de-emphasis 26 are
It is connected to the input terminal of nonlinear emphasis 4.

Now, the operation of the first clip 21 having the above-described configuration is the third
As shown in the figure, the output signal of the differential amplifier 24, to which the output signal of the LPF3 (waveform shown in FIG. 7A) is applied to its + input terminal, is clipped to a predetermined clip level (clip 6). (The same as the clip level of),
By de-emphasising the clipped signal (waveform shown in FIG. 7B) with de-emphasis 26, the signal applied to the negative input terminal of differential amplifier 24 and the input terminal of non-linear emphasis 4 is Compared with the waveform shown in FIG. 7A, the waveform shown in FIG. 7C is obtained by removing the rising portion a of the pulse.

And the de-emphasis that makes up the first clip 21
The output signal of 26 (waveform shown in FIG. 3 (C)) is passed through the non-linear emphasis 4 and further passed through the emphasis 5, so that only the high-frequency emphasized signal according to the signal level is applied in the non-linear emphasis 4. , Beyond a certain level.

Therefore, the second clip 22 suppresses the amplitude component of the signal exceeding a predetermined level.

Thus, on the recording side of the luminance signal system, the input luminance signal from the input terminal 1 can be recorded at the same amplitude level as in the standard mode even in the long time mode.

On the playback side of the luminance signal system, with clip compensation 23,
Magnetic tape 11 whose amplitude is suppressed by the second clip 22
By expanding the reproduction signal from the signal A, and compensating the signal by the amount suppressed, it is possible to reproduce a signal of good quality similar to the standard mode even in the long time mode.

The first clip 21 described above can be easily configured by using, for example, an IC of AN6306 manufactured by Matsushita Electronics Industrial.

Specific circuit examples of the second clip 22 are shown in FIGS. 4 (A) and 5 (A).

In the circuit shown in FIG. 4 (A), when a large-amplitude signal exceeding a predetermined level comes in from the input terminal in, the diode D ₁ in the circuit portion A becomes conductive, so that the input-output terminal The gain is reduced, and the amplitude of the large-amplitude input signal can be made an output signal having a predetermined amplitude or less. For this purpose, the value of the variable resistor R for setting the clip level may be set appropriately.

In the circuit shown in FIG. 5 (A), the high frequency component of the signal applied to the input terminal in is taken out at the connection point between the diode D ₂ and the diode D ₃ via the capacitor C in the circuit portion B. Therefore, even if a large-amplitude signal comes in from the input terminal, an output signal having a predetermined amplitude or less can be obtained. For this purpose, the variable resistor R for setting the level of the output signal may be adjusted appropriately. The circuit shown in FIG. 5 (A) has an advantage over the circuit shown in FIG. 4 (A) in that the output signal thereof has no second-order distortion.

As a concrete circuit example of the clip compensation 23, FIG.
And FIG. 5 (B).

The circuit shown in FIG. 4 (B) is obtained by connecting the circuit portion A shown in FIG. 4 (A) to the feedback loop of the differential amplifier D. With this structure, the second clip 22 compensates for the amplitude of the signal whose amplitude is limited.

The circuit shown in FIG. 5 (B) is obtained by connecting the circuit portion B shown in FIG. 5 (A) to the feedback loop of the differential amplifier D. Also in the circuit shown in FIG.
Compared with the circuit shown in FIG. 1B, there is an advantage that the output signal has no second-order distortion.

The clip compensation 23 shown in FIG. 4 (B) (FIG. 5 (B)) is always used as a pair with the second clip 22 shown in FIG. 4 (A) (FIG. 5 (A)). Of course, it is done.

In the block diagram of the signal processing circuit described above, the first
A case will be described below in which the purpose of the clip is achieved only by the second clip 22 without using the clip 21 of FIG.

When the clip level of the second clip 22 is lower than the emphasis amount of the emphasis 5, for example, the emphasis characteristic of the emphasis 5 is as shown in FIG. 8, and the clip level of the second clip 22 is white from the sync tip. On the side
When it is 180%, the amount of suppression of the amplitude of the signal by the second clip 22 becomes large. Therefore, in order to satisfactorily compensate this signal with the clip compensation 23 for extending the amplitude of this suppressed signal. If the compensation amount is not large as compared with the normal case, the reproducibility of the signal portion exceeding the clip level becomes poor.

Therefore, if the amount of compensation is increased, noise is also greatly expanded, so that the SN ratio at the rising and falling edges of the reproduction signal is deteriorated.

However, with the circuit according to the invention, the second clip
22 is suppressed only by the extra lifting due to nonlinear emphasis 4, so the amount of compensation is also the second
Much less than when using only clip 22.

Therefore, there is little deterioration in the above SN ratio and there is no problem in practical use, and the signal processing circuit according to the present invention has the above-mentioned inconvenience (fabricating a fine pattern in the long mode than in the standard mode). It is possible to eliminate the problem that a signal necessary for reproducing is lost and a good reproduced image cannot be obtained).

In the above description, in the long time mode, the first
The clip level of clip 25 of clip 21 is set to the clip level in the standard mode (that is, the same as the clip level of clip 6), and the high frequency part of the signal after passing through nonlinear emphasis 4 and emphasis 5 is the clip of clip 25. Although it has been stated that the second clip 22 suppresses the signal portion exceeding the level, in order to obtain the optimum clip level of the clip 25, the rising portion (edge portion) of the output signal of the emphasis 5 and the first clip 21 are configured. The level may be set according to the comparison with the rising portion (edge portion) of the output signal of the de-emphasis 26.

(Effects of the Invention) As described above, in the signal processing circuit according to the present invention, the signal can be recorded and reproduced well even in the long-time mode, as in the standard mode. It can be reproduced and a good reproduced image can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram best representing the features of the present invention, and FIG. 2 is a block diagram of an embodiment of a signal processing circuit according to the present invention.
FIG. 3 is a diagram showing the input / output waveform of each part of the first clip 21. FIG. 3 (A) shows the output signal of LPF3, FIG. 3 (B) shows the output signal of clip 25, and FIG. Is de-emphasis
26 shows output signals of 26, FIGS. 4 and 5 show circuit examples of a second clip and clip compensation 23, and FIG. 6 shows a block diagram of a conventional luminance signal system.
The figure shows a non-linear emphasis characteristic example of the non-linear emphasis 4, FIG. 8 shows the emphasis characteristic example of the emphasis 5, FIG. 9 shows the input waveform of the clip 6, and FIG. Waveform in mode,
FIG. 3B is a diagram showing waveforms in the long time mode. 4 ... Non-linear emphasis, 5 ... Emphasis, 21,2
2 ... First and second clips, 23 ... Clip compensation.

Claims (1)

[Claims] 1. A signal processing circuit in a luminance signal system of a video signal recording / reproducing apparatus for recording / reproducing in a standard mode or in a long-time mode having a recording / reproducing speed lower than the recording / reproducing speed in the standard mode, wherein the recording side , The luminance signal to be recorded is supplied to one input terminal, the differential amplifier section, the clip section for suppressing the amplitude of the output signal of the differential amplifier section at a predetermined level, and the output signal of the clip section. A de-emphasis section that outputs a signal obtained by de-emphasis to a non-linear emphasis circuit and supplies it to the other input terminal of the differential amplifier section, and clips the predetermined level of the clip section in the standard mode. A first clip circuit that is set to a level and a signal level of the output signal of the de-emphasis section that constitutes the first clip circuit. A non-linear emphasis circuit that emphasizes the high-frequency components according to the noise level, an emphasis circuit that further emphasizes the high-frequency components of the output signal of this non-linear emphasis circuit, and a first circuit that suppresses the amplitude of the output signal of this emphasis circuit at a predetermined level. A second clip circuit, and the reproduction side is configured to be complementary to the second clip circuit.
Clip compensating circuit for expanding the reproduction signal by the amount of the signal amplitude suppressed by the clipping circuit, and a de-emphasis circuit configured to complement the emphasis circuit and complementarily attenuate the high frequency component of the output signal of the clip compensating circuit. And configured to be complementary to the non-linear emphasis circuit,
A non-linear de-emphasis circuit that complementarily attenuates a high frequency component according to a signal level of an output signal of the de-emphasis circuit, in a long time mode, on the recording side, the first clipping circuit and The non-linear emphasis circuit, the emphasis circuit,
The second clip circuit is provided, and the reproducing side is provided with the clip compensating circuit, the de-emphasis circuit, and the non-linear de-emphasis circuit. Is configured such that the first clipping circuit and the emphasis circuit are not provided but the non-linear emphasis circuit and the second clipping circuit are provided, and the clip compensation circuit and the nonlinear circuit are provided on the reproducing side. A signal processing circuit, characterized in that the signal processing circuit is configured so as to pass through the de-emphasis circuit without passing through the de-emphasis circuit.