JPS6262682A - Dynamic emphasis circuit - Google Patents

Abstract

PURPOSE:To obtain constantly a good reproducing signal having no waveform distortion with a simple circuit constitution by making common a high pass filter HPF and a limitter of a dynamic preemphasis circuit and a dynamic deemphasis circuit and making common an attenuator. CONSTITUTION:During recording, a video signal inputted from an input terminal 1 is inputted to an HPF2 and an adder 5 operating only during recording through a switch circuit 26. During reproducing, the video signal inputted from an input terminal 7 is inputted to a subtracter 7 operating only during reproducing. During the recording, a dynamic preemphasis characteristic is obtained, and during the reproducing, a dynamic deemphasis characteristic is obtained. During the recording and during the reproducing, the HPF2, a limitter 3 and attenuator 4 deciding both the characteristics are commonly used, thereby even when circuit elements are dispersed, the dynamic preemphasis characteristic and the deemphasis characteristic are constantly reverse characteristics. Accordingly, a deemphasis output having no waveform distortion is constantly obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a dynamic emphasis circuit that is used in a video signal processing system such as a magnetic recording/reproducing device, improves S/H, and is suitable for integration.

[Background of the invention]

Improving the image quality of video tape recorder playback 1
As one means, a pre-emphasis circuit is provided in the recording signal processing system, and a de-emphasis circuit is provided in the reproduction signal processing system. The pre-emphasis circuit emphasizes the high frequency components of the recording signal, and the de-emphasis circuit suppresses the emphasized high frequency components and returns them to the original level, improving the s7y of the high frequency components. It is something to do.

That is, in general, the video signal is frequency modulated (CFM) I
When recording and playing back, the demodulation noise of the played back and demodulated video signal increases linearly as the frequency increases (the pre-emphasis circuit emphasizes the high-frequency components of the video signal during recording and mixes it. The de-emphasis circuit suppresses the emphasized high-frequency components of the video signal and returns them to the original level during playback.As a result, the S/N is improved.

In this way, the emphasis circuit, which is a pair of pre-emphasis circuit and de-emphasis circuit, is very useful for improving the image quality of the reproduced image of a video tape recorder, but the characteristics of these pre-emphasis circuit and emphasis circuit are Since the level of the high-frequency component is constant regardless of the level, there is a drawback that when the level is high, a high 5/A' can be obtained, but when the level is low, sufficient s7s cannot be obtained.

On the other hand, the characteristics change depending on the level of the high frequency component of the video signal, and the S
A DYNAMITSUQUEN 7 assist circuit was proposed that was able to obtain /N. (Unexamined Japanese Patent Publication No. 53-106106,
(Japanese Unexamined Patent Publication No. 55-106109) Figure 4 is a block diagram showing a dynamic pre-emphasis circuit, in which 1 is an input terminal, 2 is a high-pass filter, 5 is a limiter, 4 is an attenuator, and 5 is an adder. , 6 are output terminals.

A video signal from an input terminal 1 is supplied to a high pass filter (hereinafter referred to as HPF) 2 and an adder 5. HPF
2 separates the high frequency component from the video signal, this high frequency component is amplitude limited by the IJ transmitter 3 and attenuated by the attenuator 4. The high frequency components from the attenuator 4 are added in the adder 5,
The video signal is added to the video signal from the input terminal 1, and a video signal with emphasized high-frequency components is obtained at the output terminal 6.

Limiter 3 limits the amplitude when the high frequency component has a large amplitude,
The amplitude is not limited when the amplitude is small.

For this reason, the high-frequency components of the video signal obtained at the output terminal 6 are greatly emphasized when the amplitude of the high-frequency components of the video signal from the input terminal 1 is small; The percentage is small.

FIG. 5 is a characteristic diagram of such a dynamic pre-emphasis circuit, in which the higher the frequency of the video signal, the more emphasized it is, and the emphasized 1* changes depending on the amplitude of the frequency component, and the characteristic curve α is It corresponds to a high-frequency component with a small amplitude, and the amplitude changes to a thick characteristic curve s b *'.

HpF2 in FIG. If G(I) is the transfer function of the transmission line due to the limiter 5 and attenuator 4, input terminal 1
．． The transfer function between the output terminals 6 is 1+G(S).

FIG. 6 is a block diagram showing a dynamic de-emphasis circuit for the dynamic pre-emphasis circuit of FIG. 4, where 2' is HpF.

3' is a limiter, 4 is a subtractor, 7 is an input terminal, 8 is a subtracter, and 9 is an output terminal.

In FIG. 6, HpF2', limiter 31. Attenuator 1 4' operates in the same way as gpp2, limiter 6, and attenuator 4 shown in FIG. 4, respectively.

Therefore, since the transfer function of the transmission line consisting of BPF 2', limiter 3', and attenuator 4' is G(,9), the transfer function between input terminal 7 and output terminal 9 has the inverse characteristics of the phasic circuit. .

FIG. 7 is a characteristic diagram of the dynamic de-emphasis circuit shown in FIG. 6, in which high-frequency components that have a large amount of pre-emphasis in the dynamic pre-emphasis circuit shown in FIG. 4 have a large amount of de-emphasis.

In this way, the smaller the amplitude of the high-frequency component of the video signal to be recorded, the more the amplitude is emphasized, and as a result, the S/N of the high-frequency component is uniformly improved for all amplitudes.

FIG. 8 is a diagram showing a specific example in which the dynamic pre-emphasis circuit of FIG. 4 is integrated into an integrated circuit (IC), and FIG. 9 is a diagram showing a specific example in which the dynamic de-emphasis circuit in FIG. 6 is integrated into an IC. . In Figures 8 and 9, 10
, 11 are input/output bins of the IC, and parts that are equivalent or the same as those in FIGS. 4 and 6 are designated by the same reference numerals.

In such a configuration, the characteristics of HPF2 are that the external capacity is 1.
2 and integrated resistor 13, +) Mitsutaro's characteristics are mainly due to transistors 14°, 15, and integrated resistor 16,
The characteristics of the attenuator 4 are determined by the integrated resistors 17 and 18, resulting in the dynamic pre-emphasis characteristics shown in FIG.

On the other hand, the characteristics of the HPF 2' are determined by the external capacitor 19 and the integrated resistor 20, and the characteristics of the limiter 3' are mainly determined by the transistor 2.
1, 22, and integrated resistor 23, the characteristics of the attenuator 4' are determined by the integrated resistors 24, 25, and the dynamic de-emphasis characteristics shown in FIG. 7 are obtained.

In such a conventional configuration, the external capacity is 12,1
9 and integrated elements 16 to 18, 20 to 25 vary (
Then, the dynamic pre-emphasis characteristic and the dynamic de-emphasis characteristic vary, and the two characteristics are no longer completely opposite characteristics, resulting in waveform distortion in the reproduced signal.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to overcome the above-mentioned drawbacks of the conventional technology, it is an object of the present invention to provide a dynamic The purpose of this invention is to provide an emphasis circuit.

[Summary of the invention]

In order to achieve the above object, in the present invention, HPF2 and H
PF 2' and limiter 3 and limiter 3' are made common. Furthermore, the attenuator 4 and the attenuator 4' may be used in common, or the integrated elements that determine the attenuation degree of the attenuator 4.4' may be connected to each other in such a way that the ratio accuracy of the integrated elements is high and the two attenuation degrees are approximately equal. This constitutes an emphasis circuit.

In this way, the dynamic pre-emphasis characteristic and the dynamic de-emphasis characteristic are always reversed.

[Embodiments of the invention]

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

FIG. 1 and FIG. 2 are block diagrams each showing an embodiment of the present invention. In FIGS. 1 and 2, reference numeral 26 denotes a switch circuit for switching the two-man power between recording and reproducing, and parts that are the same or equivalent to those shown in the conventional example are given the same reference numerals.

In FIG. 1, during recording, a video signal input from input terminal 1 is passed through HPF 2 through switch circuit 26.
and an adder 5 which operates only during recording. HPF
The video signal input to EpF2, limiter 3,
Only the high frequency components are extracted via the attenuator 4 and input to the adder 5. In the adder 5, the above-mentioned two-person power is added, and a video signal with emphasized high-frequency components is output to an output terminal 6.
is output to. On the other hand, during playback, the video signal input from the input terminal 7 is input to the subtracter 7, which operates only during playback. The output of the subtracter 7 is input to the switch circuit 26, and the signal via the switch circuit 26 that is output to the terminal 9 as an output signal is Hpp 2IJ
The signal is input to the subtracter 8 via the transmitter 3 and attenuator 4. Thus, a dynamic pre-emphasis characteristic can be obtained during recording, and a dynamic de-emphasis characteristic can be obtained during reproduction. Moreover, HPF2 and IJ, which determine both characteristics,
By sharing the emitter 3 and attenuator 4 during recording and playback, even if the circuit elements that make up the HPF 2, limiter 3, and attenuator 4 vary, the dynamic pre-emphasis characteristics and dynamic de-emphasis characteristics are always opposite to each other. Becomes a characteristic. In other words, the circuit elements of HPF 2, limiter 3, and attenuator 4 vary, and the transmission function of this transmission path is G'Cr)
Then, the transfer function between input terminal 1 and output terminal 60 (at the time of recording) is 1-1-G'(,?)...(1), but the transfer function between input terminal 7 and output terminal 9 is The transfer function between (during playback) is as follows, & in equations (1) and (21) is always 1, and de-emphasis output without waveform distortion can be obtained.Moreover, Ep
By using F, limiter, and attenuator in common during recording and playback, the number of circuit elements can be significantly reduced, and when integrating, the external HpF can also be used as a capacitor, which has the effect of reducing the number of IC pins. .

It goes without saying that the input level to the HPF 2 or limiter 3 should be made equal during recording and reproduction to obtain the same limiter effect.

In FIG. 2, an attenuator 4 for recording and an attenuator 4' for reproduction are provided, and each attenuator 4.4' The ratio accuracy of the integrated element that determines the degree of attenuation of both attenuators 4.
This is a case where the attenuation degrees of 4' are made almost equal, and it is clear that the same effect as the present invention shown in FIG. 1 can be obtained. In this case, the phase can be inverted by the separate attenuators 4 and 4' by simply adding one integrated element to the present invention shown in FIG. 8 has the advantage that it can be easily configured using a differential amplifier suitable for integration.

FIG. 3 is a diagram showing a specific embodiment of the present invention shown in FIG. 2, and the same or equivalent parts as in FIG. 2 are designated by the same reference numerals. In Fig. 5, 27 is an IC pin;
28 is a shared external capacity, 29 is an extra high voltage level for recording (approximately 1V or more), and a low voltage level (approximately 0.3V) for reproduction.
The recording mode signal 3o is at a high voltage level (approximately 1 V or more) during reproduction and is at a low voltage level (approximately 1 V or less) during reproduction (approx.
V or less).

In the embodiment shown in FIG. 3, the output of the switch circuit 26 is switched by the recording mode signal 29 and the reproduction mode signal 3o, the adder 5 is activated only during recording, and the subtracter 8 is activated for reproduction. Controlled only when in operation. Also, during both recording and playback, the characteristics of gpp2 are the integrated resistor 31.
The characteristics of the IJ transmitter 3 are determined by the integrated resistor 62 and the integrated transistors 33 and 34, and the characteristics are completely the same during recording and reproducing.

The attenuation degree of the attenuator 4 is determined by the integrated resistors 35 and 56, and the attenuation degree of the attenuator 4' is determined by the ratio of the integrated resistors 37.38 and 39.40. Therefore, if the specific accuracy of these integrated resistors is made sufficiently high, both attenuation degrees will be approximately equal, and as mentioned above, HPF2 and limiter 3
Since they are shared, the dynamic pre-emphasis characteristics and dynamic de-emphasis characteristics can be made almost completely opposite, and a signal with the same waveform as the dynamic pre-emphasis input can be obtained as the dynamic de-emphasis output. In addition, by sharing, the number of external parts and integrated elements can be reduced and costs can be reduced.
Needless to say, the number of IC pins can be reduced and the unnecessary IC pins can further increase the degree of integration.

〔Effect of the invention〕

According to the present invention, even if the circuit elements constituting the dynamic emphasis characteristic vary, a good emphasis output without waveform distortion can always be obtained, and the number of circuit elements can be reduced.
A dynamic emphasis circuit that enables a reduction in the number of C bins can be realized.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing one embodiment of the present invention,
FIG. 5 is a diagram showing an example of a specific circuit configuration of the present invention,
Fig. 4 is a diagram showing a conventional dynamic pre-emphasis circuit, Fig. 5 is a characteristic diagram of the circuit shown in Fig. 4, Fig. 6 is a diagram showing a conventional dynamic de-emphasis circuit, and Fig. 7 is a diagram showing the characteristics of the circuit shown in Fig. 4. 6 shows a characteristic diagram of the circuit shown in FIG. 8. FIG. 9 is a diagram showing a specific circuit configuration of a conventional dynamic pre-emphasis circuit and a dynamic de-emphasis circuit. 1.7...Input terminal 6.9...Output terminal 2
, 2'...HPFs
, s'... Limiter 4, 4'-...
- Attenuator 5-710 n unit 6... Subtractor 10.11.27... IC pin 12.18.28... External capacitor 26... Switch circuit 29... Recording mode signal 30 ...Playback mode signal
−ゝ“・□I・・Yono Menghito Patent Attorney Katsuo Ogawa ~ 1 1 times + Figure 15 (sha) True Mu Koshumoori 9 Oni 9 Figure

Claims (1)

[Claims] A dynamic pre-emphasis circuit consisting of a first high-pass filter, a first limiter, a first attenuator, and an adder, and a second high-pass filter, a second limiter, and a second
In a dynamic emphasis circuit having a dynamic de-emphasis circuit comprising an attenuator and a subtracter, the first high-pass filter and the second high-pass filter are shared, and the first limiter and the second
In addition to making the limiter common, the first attenuator and the second attenuator may be made common, or the resistor group that determines the attenuation degree of the first and second attenuators may have high ratio accuracy. A dynamic emphasis circuit that is characterized by