JPS5870407A - Aperture correction circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aperture correction circuit suitable for a television signal reproducing device, particularly a video disc system.

In general, recording and reproducing devices have certain frequency characteristics, and in particular,
High-frequency components of the reproduced signal are attenuated due to aperture characteristics caused by the relationship between the recording medium and the reproduction head. In television signal reproducing devices such as video tape recorders and video disk systems, video signals are frequency modulated signals (hereinafter referred to as F
FM signal).
The high-frequency components of the signal are significantly attenuated, and this is one of the causes of the deterioration of the reproduced image. Therefore, in television signal reproducing equipment, an equalization circuit is installed to reduce the high-frequency components of the reproduced FM video signal. It compensates for attenuation and improves the quality of the reproduced image.

FIG. 1 is a circuit diagram showing a conventional example of an equalization circuit, in which 1 is an input terminal, 2 is a band wave generator 3 is an equalization circuit, 4 is an FM demodulation circuit, and 5 is an output terminal.

Next, the operation of this conventional example will be explained.

The reproduced F'M signal is supplied to an input terminal 1, unnecessary noise components are removed by a bandpass generator 2, and the signal is supplied to an equalization circuit 3. The equalizing circuit 3 is a resonant circuit having a resonant frequency and Q determined by a resistor R, an inductance L, and a capacitor C provided in parallel with the transistor Tr, and a resistor R provided in series between the collector of the transistor Tr and the power supply. , the attenuation of high-frequency components of the supplied FM signal is compensated for by appropriately determining the resonance frequency and Q. The FM signal compensated for high frequencies by the equalization circuit 6 is demodulated by the FM demodulation circuit 4 including a limiter circuit, and a video signal is obtained at the output terminal 5. Here, the video signal is a signal that includes a synchronization signal (the same applies hereinafter) and is in the range of 4.3 MHz white peak to 6.3 MHz, and the resonant frequency of the equalization circuit B is approximately 91 VI Hz. as 5.3M
The width is increased by approximately 3d13 at t(z).

In this way, the high-frequency attenuation of the reproduced FM signal is compensated for, and a good effect is produced for a device such as a video tape recorder in which the high-frequency attenuation characteristic can be considered to be constant.

However, since the equalizer circuit 6 is a resonant circuit with fixed characteristics because the resistor R, inductance L, and capacitor C are fixed, it provides sufficient high-frequency compensation for FM signals whose attenuation characteristics change. I can't.

In particular, when a change in amplitude occurs in the high-frequency components of the FM signal due to the attenuation characteristics, when the frequency shift of the FM signal is determined as described above, this amplitude change appears in the white level part of the video signal, and the white part of the image An inversion phenomenon occurs in which the color changes to black, degrading the image quality. Therefore, if the resonance characteristics of the equalizer circuit 6 completely compensate for the high-frequency attenuation characteristics of the playback device, no change in the amplitude of the high-frequency components of the FM signal will occur, but in reality, compensation is performed in this way. It is difficult to achieve perfection, and even in video tape recorders, a so-called double limiter circuit is used to eliminate amplitude changes in the high frequency components of the FM signal.

On the other hand, in a video disc system, the playback head moves on the recording medium (disk) while playing back, so the aperture characteristics change and the attenuation characteristics of the high-frequency components of the reproduced FM signal change. do. In other words,
The attenuation of high frequency components is greater when the reproducing head scans the inner circumference of the disk than when it reproduces the outer circumference of the disk. If the attenuation characteristics of the high frequency components of the FM signal change in this way, it is not possible to compensate for this with the conventional equalization circuit shown in Figure 1, and the attenuation towards the inner periphery of the disc changes. The change in amplitude of the high-frequency component of the FM signal due to the characteristics becomes large, making it difficult to remove with a double limiter circuit.

In contrast, the characteristics of the equalization circuit are changed by the control signal representing the playback scanning position of the playback head using address signals recorded for each track on the disk and potentiometers linked to the movement of the playback head. FM
Techniques have been developed to compensate for the attenuation of high-frequency components of signals.

However, in these techniques, the obtained control signal is
It is difficult to accurately correspond to the attenuation characteristics of the high-frequency components of the M signal, and the configuration becomes complicated.In addition, when the playback head is replaced, the attenuation characteristics also change depending on the playback head. Adjustments must be made every time the playback head is replaced.

It is an object of the present invention to eliminate the drawbacks of the above-mentioned prior art and accurately attenuate the high-frequency components of the reproduced FM signal with a simple configuration even if the attenuation characteristics of the high-frequency components of the reproduced FM signal change. An object of the present invention is to provide an aperture correction circuit capable of compensation.

In order to achieve this object, the present invention provides a variable equalization circuit, detects a control signal directly from the reproduced signal, and changes the characteristics of the variable equalization circuit using the control signal to improve the FM signal in the reproduced signal. The feature is that it compensates for the attenuation of high frequency components.

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

FIG. 2 is a block diagram showing an embodiment of the aperture correction circuit according to the present invention, in which 6 is a trap circuit, 7 is a bandpass waveform generator, 8 is a variable equalizer circuit, 9 is a limiter circuit,
10 is an FM demodulation circuit 11 is a frequency conversion circuit, 12 is an amplifier circuit, 13a and 13b are envelope detection circuits, and 14 is a differential amplifier.The same parts as in FIG. 1 are designated by the same reference numerals.

FIG. 3 is a circuit diagram showing an embodiment of the variable equalizer circuit 8 in FIG.
is a coil, and 21 is a resistor.

Next, the operation of this embodiment will be explained.

In FIG. 2, a reproduction signal from a video disk (not shown) is supplied to an input terminal 1, consisting of an F'M video signal of 2 to 10 Mllz and an FM audio signal of a carrier frequency of approximately 7R+N11z. This playback signal is approximately 716kll
The signal is supplied to the track circuit B of Z, the FM audio signal is removed, and the signal is supplied to the band transducer 2 to obtain the FM video signal.

As mentioned above, the high-frequency components of the FM video signal have different attenuation depending on the playback scanning position of the playback head (not shown), but the characteristics change depending on the control signal from the differential amplifier 14. The signal is supplied to a variable equalizer circuit 8, which compensates for the attenuation of high-frequency components. FM with compensated high-frequency component attenuation
The video signal is amplitude-limited by the limiter circuit 9 and supplied to the FM demodulation circuit 4, where the video signal is demodulated and supplied to the output terminal 5.

Well, the playback signal of input terminal 1 has a center frequency of about 716.
The FM demodulation circuit 1o demodulates the audio signal.

A control signal for changing the characteristics of the variable equalizer circuit 8 is generated as follows.

The FM video signal separated by the band transducer 2 is detected by the envelope detection circuit 13a, and the detection output signal is supplied to the negative input terminal of the differential amplifier 14.

On the other hand, the FM audio signal separated by the band transducer 7 is converted to the same frequency as the carrier frequency of the FM video signal by the frequency conversion circuit 11, amplified by the amplifier 12, and then the envelope detection circuit 1
3b, and the detected output signal is supplied to the positive input terminal of the differential amplifier 14. The differential amplifier 14 compares the amplitudes of the two input signals, and subtracts the amplitude of the detection output signal of the envelope detection circuit 13a from the amplitude of the detection output signal of the envelope detection circuit 13b, and the difference signal is variable as the above-mentioned control signal. The signal is supplied to the equalization circuit 8.

Incidentally, in a video disc system, as the reproducing head changes the reproducing scanning position, the aperture characteristic changes and the attenuation characteristic of high frequency components changes, but the aperture characteristic has no effect on low frequency signals. Therefore, in a high frequency FM video signal, due to a change in the aperture characteristic due to a change in the reproduction scanning position of the reproduction head, the attenuation characteristic of the high frequency component changes and a change appears in the envelope.
On the other hand, since the low frequency FM audio signal is not affected by the aperture characteristics and has a constant envelope, the control signal obtained from the differential amplifier 14 represents the attenuation of high frequency components due to the aperture characteristics. It becomes a signal.

Well, even if the aperture characteristics change as a result of replacing the playback head, the envelope of the FM audio signal will not change, only the amplitude of the FM video signal will change, so the control signal will change the aperture characteristics due to the change of the playback head. It will also represent

In this way, the variable equalizer circuit 8 compensates for the attenuation of the high frequency components of the FM video signal even if the aperture characteristics change. Of course, even when the playback head is scanning a certain track, there is an attenuation characteristic of high-frequency components due to the aperture characteristic, which can be considered constant during that period.As a result, the high-frequency components of the playback signal Although fluctuations in amplitude occur as in a video tape recorder, fluctuations in the amplitude of the high frequency component cause a change in the envelope of the FM video signal, and this can also be compensated for by the variable equalizer circuit 8.

In FIG. 6, the input terminal 15 of the variable equalizer circuit 8
An FM video signal is supplied from the band p-wave generator 2 (FIG. 2), and an input terminal 16 is supplied with a control signal from the differential amplifier 14 (FIG. 2). The variable capacitor 18, the coil 20, and the resistor 21 constitute the variable equalization circuit 8, which constitutes a resonant circuit, and includes envelope detection circuits 13a and 13 in FIG.
When the detection output signals of b are equal, the resonance frequency is approximately 5M.
The inductance of the coil 20, the resistance value of the resistor 21, and the DC voltage supplied to the variable capacitor 18 are determined so that IIz.

When the high-frequency component is attenuated due to the aperture characteristic, the amplitude of the control signal from the input terminal 16 increases, which causes the capacitance of the variable capacitor 18 to decrease, and as a result, the resonant frequency increases. changes and lifts high frequency components.

Note that the capacitor 19 is for blocking the control signal from the input terminal 16.

Although the explanation here relates to video discs, the invention is not limited to this. The present invention can also be applied to playback devices.

As explained above, according to the present invention, the attenuation characteristic of the high frequency component due to the aperture characteristic is directly detected from the reproduced signal,
This performs high-frequency compensation by changing the characteristics of the equalization circuit, so the aperture characteristics can be detected accurately with a simple configuration, and as a result, a high-quality reproduced image without white level inversion can be obtained. It is possible to provide an aperture correction circuit with excellent functionality except for the technical drawbacks.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional example of an aperture circuit, Figure 2 is a circuit diagram showing a conventional example of an aperture circuit.
3 is a block diagram showing an embodiment of the aperture circuit according to the present invention, and FIG. 3 is a circuit diagram showing an embodiment of the variable equalization circuit of FIG. 2. 2.7...Band filter 8...Variable equalization circuit 13a, 13b...Envelope detection circuit 14...Differential amplifier 2 Figure 2

Claims (1)

[Scope of Claims] (1) A composite signal consisting of a low frequency signal and a high frequency signal reproduced from a recording medium is supplied, and high frequency components of the high frequency signal are attenuated due to aperture characteristics during reproduction from the recording medium. The aperture correction circuit for compensating for this includes a circuit for separating a low frequency signal and a high frequency signal from the composite signal, and a circuit for detecting and comparing the amplitudes of the low frequency signal and the high frequency signal to generate a control signal. and a circuit for compensating the attenuation of the high-frequency component of the high-frequency signal that is controlled by the control signal, and also compensates for the change in the attenuation of the high-frequency component of the high-frequency signal that accompanies a change in the aperture characteristic. An aperture correction circuit characterized in that it is configured to be capable of compensation. (2. Claim 1, wherein the aperture correction circuit is characterized in that the low frequency signal is an FM audio signal, and the high frequency signal is an FM video signal. (3) Claim 1. 2. The aperture correction circuit according to item 1, wherein the recording medium is a disk-shaped recording medium.