JPS60145779A - Video signal regeneration circuit - Google Patents

Abstract

PURPOSE:To suppress occurrence of the inversion phenomenon without deteriorating the S/N by making variable equalizer characteristics which are added to a regeneration FM video signal linearly or nonlinearly in accordance with a demodulation video signal. CONSTITUTION:An output regeneration FM video signal of a preamplifier 9 is supplied to a dynamic equalizer circuit 21 through a delay circuit 17, and it is supplied to an equalizer circuit 16 inside a regeneration video signal level detection circuit 15. The level detection circuit 15 is connected to the equalizer circuit 16, a limiter 18, an FM demodulation circuit 19 and a low-band filter 20 longitudinally. The demodulation video signal of the regeneration FM video signal is supplied to the dynamic equalizer circuit 21 as the level detection signal from the low-band filter 20. Although the equalizer circuit 16 is the conventional type, the circuit 21 is a circuit which makes variable the ratio of the level strength for low-band frequency components for high-band frequency components of the input regeneration FM video signal linearly or nonlinearly.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video signal reproducing circuit, and particularly relates to a video signal reproducing circuit.
The present invention relates to a video signal reproducing circuit having an equalizer characteristic that relatively increases the level of high frequency components compared to low frequency components for a video signal of a frequency modulated wave.

PRIOR ART FIG. 1 shows a block system diagram of an example of a conventional video signal recording and reproducing device.
Here, after unnecessary high frequency components are removed, the signal is supplied to the pre-emphasis circuit 4.

The pre-emphasis circuit 4 is a circuit that provides a predetermined emphasis characteristic that converts high-frequency components into low-frequency components and relatively enhances them in order to improve the signal-to-noise ratio (S/N). As a result, the output signal waveform becomes a waveform with overshoots and undershoots in which the edge portions of the horizontal bright signals al and a2 are emphasized, as shown in FIG. 2, for example.

The output video signal of this pre-emphasis circuit 4 is supplied to a frequency modulation circuit 5. The frequency modulation circuit 5 is shown in FIG.
), and the black level of the human video signal as shown in (A) of the same figure is 3.4M Hi.
, for the white level, it is 4.4M11/a video signal (1-M
Generates and outputs a video signal).

The IM video signal is sent to the recording amplifier and rotary 1 to lance (
The rotating head 6
J is supplied to this and recorded on the magnetic deso 7.

FMll! supplied to this rotating head 6! l! Sono (No. 8's frequency spectrum is!! As shown in Figure 4 (Δ), the carrier wave shift band ■, upper sideband II LJ, and G sideband ■L
Consisting of

Next, to explain the operation of m raw silk, the weak video signal reproduced from the magnetic Chigua by the rotary head 8 is amplified to a required level by the preamplifier 9 and then supplied to the E1 riser circuit 10.

The rotary head 8 has an inductance characteristic with a low Q, and also has deso- ment and loss such as gap loss and spacing loss.
Due to the loss caused in the head system, it exhibits a high-frequency attenuation characteristic, and as a result, the frequency spectrum of the manually reproduced FM video signal of the preamplifier 9 becomes as shown in FIG. 4 (F3). Here, the high frequency component in the recorded video signal is S/N
Although this is emphasized for improvement, in addition to the above-mentioned high frequency reduction reproduction characteristics, the carrier wave level may be attenuated when comparing the side wave 41 to the level of the reproduction [M video signal], and in that case, the high frequency Some frequency components may exist within the upper and lower limiting levels of the limiter 11 at the subsequent stage and may not be limited.

Then, the output of limiter 11 is 1”lv+ll!l!
The Kl f-i signal is supplied to the M demodulation circuit 12.
Since the signal portions not subject to the above limits 1 to 1 are not supplied, this is 1: Since the M demodulation circuit '12 performs the C demodulation operation at a low frequency, the demodulated output video signal of the part A is black. The reproduced video @Mizuki waveform is outputted to the output terminal 14 through the low-pass filter 13. It is well known that the above-mentioned phenomenon of falling to black is a phenomenon that occurs at the rising portion from black to white and is called inversion, and the white image portion appears black, making the image extremely difficult to see.

Therefore, conventionally, the equalizer circuit 10
The sleeve i1? J
It was common practice to sing the equal Ir komatake, which enhances the high frequency components. J-su to this
Equalizer circuit 10 output horn reproduction FM1! Statue lti >
The frequency spectrum of No. 4 is as shown in FIG. This prevents the reversal phenomenon.

Problems to be Solved by the Invention However, the equalizer circuit 10 is designed to prevent the inversion phenomenon.
A high frequency enhancement characteristic that enhances the upper sideband components is added, but at the same time noise is also enhanced.
There is a problem in that the S/N of the demodulated video signal output from the FM demodulation circuit 12 is poor. 1, in order to improve the S/N, the amount of pre-emphasis in the pre-emphasis circuit 1 can be increased, but as the high frequency components are also enhanced and recorded accordingly, the inversion phenomenon becomes more likely to occur. On the other hand,
In order to prevent an inversion phenomenon from occurring, the equalizer characteristics of the equalizer circuit 10 are adjusted to enhance the high frequency range 4? I-sex take S/N
There was a problem that was contradictory to LL, which was that it made things worse.

Therefore, the present invention provides reproduction FMII! according to the demodulated video 4G level! l! To vary the equalizer characteristic that affects the image signal linearly or non-linearly, 1. The purpose of this invention is to promote a video signal reproducing circuit that solves the above problems.

Means for Solving the Problems The present invention provides a level detection circuit that demodulates a frequency modulated video signal reproduced from a recording medium to obtain the demodulated signal, and an output level detection signal of the level detection circuit. is supplied as a control signal, and the rate at which the level of the high frequency component of the reproduced Ic frequency modulated video signal is enhanced is varied linearly or non-linearly in accordance with the level of the level detection signal. It consists of an equalizer circuit that goes out to a limiter, and the fifth embodiment will be described below with reference to one embodiment.
This will be explained with reference to the drawings below.

Embodiment FIG. 5 shows a block diagram of an embodiment of the circuit of the present invention. In the figure, the same components as those in FIGS. In FIG. 5, the output reproduction FMIII of the C1 preamplifier 9! The image signal is supplied through the delay circuit 17 to the dynamic eye 15411 circuit 21 which constitutes the main part of the present invention, and is also supplied to the equalizer circuit 10 in the reproduced image signal level detection circuit 15. The level detection circuit 15 includes an equalizer circuit 16. Limiter 18. F
The M demodulation circuit 19 and the low-pass filter 20 are connected in cascade, respectively.
The demodulated video signal of the M video signal is supplied to the dynamic equalizer circuit 21 as a level detection signal.

Here, the 119411 circuit 16 has substantially the same fixed equalizer characteristics as the conventional equalizer circuit 10. .

On the other hand, the dynamic equalizer circuit 21 calculates the level enhancement ratio of the high frequency component to the low frequency component of the human-powered angle-accompanied FM video IS signal to the level of the level detection signal (the level of the demodulated video signal). This is a circuit that changes linearly or non-linearly according to 11 changes. In addition, crime circuit 17
J5 is provided to correct the delay time by the level detection circuit 15, and the level detection signal from the low-pass filter 2o is supplied to the dynamic equalizer circuit 21!
A delay time is selected such that the level information at time ζ exactly indicates the level of the reproduced FM video signal at the time when it is taken out by the delay circuit 17J. The cutoff frequency of low pass filter 20 may be different from that of low pass filter 13.

FIG. 6 shows a circuit diagram of a first embodiment of the dynamic equalizer circuit 21. In the same figure, the reproduced IM video signal from the delay circuit 17 that enters the input terminal 22 is supplied to the base of the NPNI transistor Q+. Ru.

The emitter of this transistor Q+ is resistor R+ and coil L
It is grounded via a series resonant circuit made up of a 1 and a 7-tube vc, and is also grounded via a resistor R2.

The capacitance value of the varicap VC is varied according to the level of the level detection signal from the input terminal 23. Here, when there is a white level on the level detection side (when the level is high), the capacitance value of the variable IX7 horn VC is controlled to be small. Lucta resistance 1<3 and 1
The high frequency component of the I/M video signal output to the output terminal 24 of the transistor Q1 is enhanced as shown by ■ in Fig. 7, and the frequency characteristics of the I/M video signal are enhanced.
will be removed.

Others/J, when the level detection signal is on the black level side and the small level is high, the capacity of the varicap vC is j: l l
ll'i is controlled by a person, and the I'-sizer circuit shown in FIG. 6 has a frequency characteristic in which the resonant frequency vlfo has shifted to the lower frequency side, as shown at 1v in FIG. As described above, according to this embodiment, the frequency characteristic as shown in FIG. J') and output to the output terminal 24.

FIG. ε3 shows a circuit diagram of a second embodiment of the dynamic equalizer circuit 21. In the figure, the same components as those in FIG. 6 are denoted by the same reference numerals, and the explanation thereof will be omitted. The emitter of the transistor Q2 is grounded through the capacitor C1 and the resistor R4 in series, and the connection point between the capacitor C+ and the resistor R4 is connected to the field effect transistor For example, the drain of T ) (:) 3 is connected. The level detection signal (demodulated video signal) that has entered the input terminal 23 is applied to the gate 1- of F E I-Q 3, which is grounded, via a resistor R5, and its internal resistance is variably controlled. , l"1FTQ3 has an internal resistance value that is controlled to be small when a large level input is made on the white side, and the coil l"
,,21 C+, resistance [(4) and the above-mentioned internal resistance, etc.The Q of the resonant circuit becomes large.As a result, the initializer circuit shown in Fig. 8 becomes like the curve VC shown in Fig. 9. ,
] (circular frequency near 0 (for example, 4.5M1-12A)) (exhibits human Q resonance characteristics, and as a result, the manually reproduced FM video signal from the input terminal 22 has its high frequency components enhanced and becomes 1 - Collector J of transistor Q2 is output to output terminal 25.

On the other hand, when the level detection signal is at a low level on the black level side, contrary to the explanation in ``-'', the small equalizer circuit shown in FIG. curve Vl
As shown in the figure, the resonance 'Rf! t indicates the C-1 black level of η, and the old 'LtM video signal is outputted to the output terminal 25) without being enhanced with high frequency components and CJ. In this way, according to the present embodiment, the damping resistor (N E T' Q
By changing the parallel combined resistance of internal resistance 3 and R4)+:ζj, the resonant frequency 0 is fixed,
Only Q imparts a frequency characteristic as shown in FIG. 9 to the input reproduced FM video signal and outputs it to the -C output 9μj 25.

In addition, FIG. 10 shows the third component of the divemic equalizer circuit 21.
With the frequency characteristics of the example, Baliki 17
The capacitance b1 value of the varicap is variably controlled by the level detection signal using a knob.When playing on the white level side, the cut-off frequency is controlled to a higher frequency as shown by the broken line ■ in the same figure. Also, when playing back on the black level side, the solid line in the figure
The dust shielding frequency is controlled to move toward the lower frequency side as shown in FIG.

Furthermore, FIG. 11 shows the fourth part of the dynamic equalizer circuit 21.
Frequency characteristics of the embodiment @C1 Direction: When the frequency of the dip in the C1 region frequency is reproduced at the own level, the broken line IX becomes smaller as shown by M, and as it goes from the own level to the black level, I gradually becomes smaller, and the black level becomes 9 again. At times t, ↓ as shown by the solid line X, the frequency characteristics become louder. According to FIGS. 10 and 11, the dynamic equalizer circuit with each frequency characteristic is similar to the dynomic equalizer circuit shown in FIGS. 6 and 8.
When the signal level is on the white side, the high frequencies are further enhanced,
When it is on the black side, it reproduces an equalizer characteristic that reduces or attenuates the level enhancement m of high frequencies F M l1lI! Output as added to the @ signal.

The output reproduced FM video signal of the dynamic equalizer circuit 21 is transmitted to the limiter 11. The demodulated image 11+ signal is outputted to the output terminal 14 through the FfV1 demodulation circuit 12 and the low-pass filter 13, respectively. Dynamitsukui” riser circuit 21 is installed (
By doing so, it is possible to prevent inversion when reproducing high-level video signals, and when reproducing black-level video signals, the high frequency components are not level-enhanced, so demodulated video (14! It is possible to improve the S/N of the tag.

A1 (Phase complement 1 of dynamic equalizer circuit 21)
If one circuit is set up (No, I), and the characteristics of the rise are varied, the phase characteristics of the I/O complementary (n) may also be varied continuously or stepwise. A circuit diagram of an example of a phase compensation circuit is shown in J0. The collector of transistor Q4 is
3. The output terminal J is connected to the output terminal 27 through the resistor R6 and the conductor C3 in series.
"Connected to 27.

The phase correction circuit of the mouth (in Fig. 13, the solid line
The resonant frequency is determined by the value of 2 [the phase characteristic of -180° with r]. This phase characteristic
By varying t fin according to the characteristics of EJ, high-quality images can be obtained because ringing etc. are greatly reduced. , or step by step? The selection depends on the IJ raw image quality.As shown in FIG. 12, the amplitude-frequency characteristics of the phase correction circuit exhibit a flat characteristic as shown by the solid line Xi in FIG. 13. 0 Application example Although emitter peaking is used in each embodiment C in FIGS. 6 and 8, a parallel 911 vibration circuit may be connected to the collector to perform the same operation as in -C. , the delay circuit 17 is unnecessary when there is almost no time delay in the level detection circuit 15, and the output video signal of the low-pass filter 12 can be fed back.Furthermore, the characteristics of the dynamic equalizer circuit 21 can be varied. Although it has been explained that the level of the demodulated video signal should be avoided in a linear manner, it is also possible to make a non-linear change such as only changing the level above the level (for example, above the white level). J, yes.

According to the present invention, the high frequency components of the internal FM video signal are increased or decreased linearly or by:11 according to the demodulated video signal level. i
f! Since I set up a 1F circuit,
Demodulated video ICS: High frequency components are enhanced when the signal level is high (white level or that level), and high frequency components are enhanced when the demodulated video signal level is low (black level or its fJ 31i level). It is possible to reduce the high-frequency components and prevent the level from being enhanced, and to prevent the inversion when reproducing a video signal at a level close to the white level IJ, zono (= J1). When a video signal at the black level or a level close to the black level is reduced by 1η, the noise on the 6th band side does not need to be enhanced, so the S/N of the demodulated video signal is not deteriorated, and this prevents inversion, which was conventionally possible. and S/I
'Ug4h1shi (itai) to balance with J improvement'
Compared to the Li+1 circuit, the S/ of the demodulated video signal on the black level side is
In addition to improving N, the probability of occurrence of the reversal phenomenon can be further reduced; The frequency component of the difference is F' M
The crosstalk level is taken out from the demodulation circuit, and its crosstalk level is determined by the carrier frequency and the register A of the crosstalk component, and since the present invention particularly emphasizes the high carrier wave frequency, 1-IVLt! The -1 stoke level at the output circuit of the control circuit can be relatively reduced, which is the reason for the many features of C.

[Brief explanation of the drawing]

Fig. 1 is a block system diagram showing an example of a conventional video signal recording iQ raw wave device, Fig. 2 is a diagram showing an example of the output video signal waveform of the pre-induction assist circuit, and Fig. 3 (△), (B) are the input video signal waveform and input level versus output frequency of the frequency modulation circuit, respectively. Figure 4 <A
) to (C) are diagrams showing the frequency vectors 1 to ul\ of the output signals of each part in FIG. 1, respectively, and FIG. Figures and Figure 8 are roughly 5th.
Examples of the dynamic equalizer circuit in the figure are shown below.
Figures 7 and 9 are schematic diagrams of Figures 6 and 8, respectively]
Figures 10 and 11 show the frequency characteristics of the 1st path.
The figure shows the frequency Q of another embodiment of the Riley circuit: If! Fig. 12 is a circuit diagram of the phase correction circuit with 191 reduced, and Fig. '13 is a diagram of the circuit shown in Fig. '12.
i19ru. 1...Video signal human power +2iJ', /I...Sirl shift 19f circuit,! 5...Frequency modulation circuit, 10.16
...Equal circuit, 11.18...Limiter,
12.19... [-N4 demodulation circuit, 14... Re-cow video 1'l (7i output terminal, 15]...111 cow video signal level detection circuit, 17... extension circuit, 21 ...
Dino Mitsukui, 1 Riley "Circuit, 22...11
g FM video signal input terminal, 23...Level detection 1
No. 5 input terminal, 24.25...output terminal. Koma, i' [Applicant: Japan Victor Co., Ltd. Agent]
Patent Attorney Tadahiko Ito Procedure Procedure Yama 1 JEffi (Method) 1. ! Display of Jifl 1981 Special revision request No. 1779 2 Name of the invention Video signal reproducing circuit 3.7 Yamasho wo Surusha Special J1 Applicant 11 Location 12fR 3 Old Moriyacho, Kanayō Ward, Yokohama City, Kanagawa Prefecture 221 Place name (432) Japan Victor Co., Ltd. Representative Director and President Michi Shishi - Department 4, 11 agents 〒102 Chiyo, Tokyo [5-7 Kojimachi, 0-ku] 5. Supplement 113 Date of Order A1 March 27, 1980 (shipping date) 6. Column for a brief explanation of the drawings in the specification subject to amendment. "Figure 3 (A>, <8)" is corrected as (Figure 3 ()).

Claims (1)

[Claims] The recorded edge frequency modulated video signal reproduced from the recording medium with attenuation of high frequencies is passed through a limiter to U F M
4! In the video signal reproducing circuit that supplies the demodulated video signal to the i modulation circuit and obtains the demodulated video signal output, the regenerated 1-open frequency modulated video signal is +7M demodulated and the demodulated signal is The output level detection signal of the level detection circuit is supplied as a control signal, and the ratio of level enhancement of the C high frequency component to the reproduced frequency modulated video signal is controlled linearly or A circuit in a video signal that is characterized by an irregular change in tIC and output to the limiter.