JPH03230371A - Fm modulated brightness signal processing circuit - Google Patents

Abstract

PURPOSE:To process an inversion preventing signal without deteriorating the SN ratio, waveform characteristic and frequency characteristic of a demodulated signal by switching two inversion preventing circuits in accordance with the level of an FM modulated brightness signal. CONSTITUTION:When the level of an FM modulated brightness signal applied from an HPF 4 is higher than -6dB, a dropout detector 5 switches the contact (c) of a change-over switch SW1 to the 1st inversion detecting circuit K1 side and switches the contact (f) of a change-over switch SW2 to the equalizer 17 side. When the signal level from the HPF 4 is -6 to -12dB, the detector 5 switches the contact (c) to the 2nd inversion preventing circuit K2 side and holds the contact (f) on the equalizer 17 side. In the case of less than -12dB, the detector 5 holds the contact (c) on the circuit K2 side and switches the contact (f) to the 1H delay circuit 11 side. Consequently, a reproducing signal can be prevented from being whitened without deteriorating the SN ratio or the like of a reproduced brightness signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an FM modulation luminance signal processing circuit that performs inversion prevention signal processing and is suitable for application to VTRs and the like.

:Summary of the Invention] The present invention is based on a first amplitude limiting circuit that receives an FM modulated luminance signal reproduced from a recording medium and limits an amplitude portion of the FM modulated luminance signal that is equal to or greater than a predetermined amplitude. Suppressing the low frequency component of the output signal of the amplitude limiting circuit No. 1,
The amplitude of the high frequency component of the FM modulated luminance signal reproduced from the recording medium is emphasized based on the first inversion prevention circuit having a high-pass filter fed back to the input end of the first amplitude limiting circuit. based on a second inversion prevention circuit having a second amplitude limiting circuit that limits a portion of the output signal of the high frequency enhancement circuit having a predetermined amplitude or more;
Based on the amplitude detection circuit that detects the amplitude of the FM modulated luminance signal, based on the output signal of the amplitude detection circuit, and based on the output signal of the first anti-inversion circuit, the output signal of the second anti-inversion circuit. and a demodulation circuit that selectively outputs the output signal of the switch circuit based on the switch circuit that selectively outputs the output signal of the switch circuit. The output signal of the first inversion prevention circuit is output, and the FM modulation luminance signal is output, and the output signal of the second inversion prevention circuit is output when the level of the F Ni modulated luminance signal is equal to or higher than a predetermined value C. It is possible to perform signal processing to prevent inversion, which would otherwise degrade the frequency characteristics of the brightness and brightness signal obtained by outputting the brightness signal and the waveform, as well as the frequency characteristics of the FM modulated brightness signal. This reduces noise generated on the screen.

[Background Art] In a conventional VTR, a luminance signal is FM modulated, a carrier chrominance signal is subjected to low frequency conversion, the FM modulated luminance signal and the low frequency converted carrier chrominance signal are combined, and an inclined trunk is recorded on a magnetic tape. Recording was performed using a rotating magnetic head so as to form a .

In this case, a high signal-to-noise ratio has been achieved by applying strong bias to the luminance signal to emphasize high frequencies and performing FM modulation with a high deviation range.

By the way, in the horizontal direction, it suddenly changes from black to white.
Based on multiplying the luminance signal of the image by the brightness factor 7.sup., over/neat occurs at the starting edge of the white signal at the boundary line between the black signal and the white signal.

Since the luminance signal subjected to such pre-ninphasis is subjected to FM modulation, the frequency of the open neat corresponding portion of the FM modulated luminance signal becomes extremely high.

However, when such an FM modulated luminance signal is recorded on a magnetic tape and then reproduced, the frequency of the reproduced FM modulated luminance signal becomes abnormally high due to the low frequency emphasis effect of the magnetic tape/magnetic head system. Since the level of this part is extremely low, when the reproduced FM modulated signal passes through the limiter, the part where the level is extremely low crosses zero and becomes 1; During demodulation, it is demodulated as a black level signal.

Therefore, based on FM demodulating the reproduced FM modulated luminance signal by FM demodulation, and then de-emphasizing it by de-emphasis, the obtained luminance signal is supplied to the monitor snow catcher. In the part where you move to Kamiyo □
, a large number of black streaks extending in the horizontal direction are formed. This is an inversion phenomenon (white peak inversion phenomenon).

Hereinafter, a conventional FM demodulation signal processing circuit provided with an inversion prevention circuit will be explained with reference to FIG. (
1) is a magnetic tape that is wound at a predetermined winding angle around a tape guide drum equipped with a rotating magnetic head and guided. The color video signal reproduced by the rotating magnetic head (2) from the inclined track of the magnetic tape (1) is supplied to the no.1 pass filter (4) via the reproduction amplifier (3), and the reproduced luminance signal is extracted. be done. The reproduced color video signal from the reproduction amplifier (3) is supplied to a low-pass filter (not shown) to extract a low-pass converted carrier color signal.

The reproduced luminance signal from this bypass filter (4) is sent to a dropout detector (5) and a limiter (7), which will be described later.
is supplied to

This limiter (7) is connected to the subsequent bypass filter (
19) together form an inversion prevention circuit. Rimi Tsuta (7)
) and the bypass filter (19), the reproduced luminance signal is demodulated by the FM demodulator (14), and the obtained luminance signal is passed through the de-emphasis circuit (15) and the low-pass filter (16) to the equalizer (bi-channel). is supplied to The reproduced brightness signal of this equalizer (17) is output to the output terminal T via the switch SW2.

is output to.

The dropout detector (5) includes a bypass filter (4).
) When the level of the reproduced brightness signal exceeds a predetermined level, the movable contact f of switch SW2 is switched to the fixed contact d side, which is connected to the output side of the equalizer (17), and when it is below the predetermined level, , switches the movable contact f of the switch SW2 to the fixed contact e side.

(18) is IH (H is horizontal period) delay device (IH memory)
And output terminal T. The luminance signal output from the bypass filter (4) is delayed by lH and supplied to the fixed contact e of the changeover switch SW2, and when the level of the luminance signal from the bypass filter (4) is below a predetermined level, the dropout detector (5) detects the luminance signal. Based on the signal that causes the movable contact f of the switch SW2 to switch to the fixed contact e, the output terminal T is output. I of the reproduced luminance signal
The reproduced luminance signal before H is output.

In the inversion prevention circuit shown in FIG. 3, which consists of a limiter (7) and a bypass filter (19), the limiter (7)
) Bypass filter (
19) emphasizes the high range and restores the zero cross in the part where the level is extremely low, thereby preventing the reversal phenomenon.

However, for example, high band 8 mi IJ V T
In R, the frequency of the overshoot corresponding part of the FM modulated luminance signal is 8 MHz or more, which is 8 MHz or higher than the normal 8 MHz! JVTR
This is significantly higher than the 5.5 MHz of that of .

Therefore, the bypass filter (19) emphasizes the high frequency range of the FM modulated luminance signal from the limiter (7) to prevent the inversion phenomenon. /N decreases or waveform characteristics deteriorate.

Reversal prevention circuits that eliminate such drawbacks have been proposed in the past. That is, as shown in FIG. 4, the C-regenerated FM modulated luminance signal from the bypass filter (I) similar to that in FIG. A bypass filter (4) similar to that in FIG. It is added to the FM modulated luminance signal. Incidentally, a reversal prevention circuit similar to this is described in Japanese Patent Application No. 311582 (1982).

The inversion prevention circuit shown in FIG. 4 exhibits a flat frequency characteristic when the level of the FM modulated luminance signal is higher than a predetermined level, so that the S/N of the luminance signal may decrease or
There is no risk that the waveform characteristics will deteriorate, and the lower the level of the FM variable xi luminance signal, the higher the
In the case of TR, the frequency characteristic is such that high-frequency components around 10 MHz are emphasized, so that the inversion phenomenon can be prevented.

Next, with reference to FIG. 5, another conventional inversion prevention circuit (see Japanese Patent Application Laid-open No. Sho E6-61010) will be described.

3'
After boosting the high frequency range by supplying it to the high frequency amplification circuit (l) as a booster through a soft limiter (!0) of approximately and its output is supplied to an FM demodulator (14) similar to that shown in FIG.

According to such an inversion prevention circuit, a soft limiter (13)
Since the high S/N upper sideband of the reproduced FM modulated luminance signal is reproduced, there are parts in the reproduced FM luminance signal from the bypass filter (4) where the level is small and there is no zero crossing. However, even if the zero cross is restored and supplied to the booster (11), there is no risk that the S/N will decrease. And the high S obtained in this way
/N (7) Hard limiter for FM modulated luminance signal (13)
Even if the pre-emphasized luminance signal is supplied to the FM demodulator (14) through the FM demodulator (14), there is no possibility that the overshoot portion of the pre-emphasized luminance signal transition from the black signal to the white signal during recording will be FM demodulated as a black signal during playback. One, N.

2. Problems to be Solved by the Invention 2. By the way, based on the use of the inversion prevention circuit shown in FIG. 4 in place of the limiter (7) and bypass filter (19) in the conventional example shown in FIG. A problem arises. That is, at the time of dropout, the bypass filter (4
) Since the level of the FM brightness signal reproduced by the color decreases significantly, the frequency of the FM modulated brightness signal supplied to the FM demodulator (14) is 8.7M in the case of a high band 8mm VTR.
Hz (the frequency of the FM modulated luminance signal corresponding to the white level is 7.7 MHz), so based on the Threslenjord level at the dropout detector (5) being lowered to, for example, -6.5 dB. Immediately before the movable contact f of the switch SW2 in FIG. 3 switches to the fixed contact e, the image of the transition part of the dropout temporarily appears white.

Therefore, it is common practice to set the Threnjord level in the dropout detector (5) higher. Since the signal is switched to the C side, interpolation is performed using the vertically uncorrelated mouth luminance signal at the time of dropout.

On the other hand, in the conventional example on the third surface, the limiter (7)
The following problems arise based on the use of the fifth inversion prevention circuit instead of the bypass filter (8).

When the inversion prevention circuit shown in Fig. 4 is replaced with the limiter (7) and bypass filter (19) shown in Fig. 3, when the level of the reproduced FM modulated luminance signal from the bypass filter (4) is sufficiently high, the bypass filter (9) is almost non-existent, so there is no deterioration of the frequency characteristics of the FM modulated luminance signal.
and bypass filter (19), even if the level of the reproduced FM modulated luminance signal from the bypass filter (4) is sufficiently high, the high frequency emphasis function of the booster (11) is working, so the FM modulation Deterioration of the frequency characteristics of the luminance signal cannot be avoided.

However, if the limiter (7) and bypass filter (19) in Figure 3 are replaced with the inversion prevention circuit in Figure 5, even if the level of the dropout detector (5) is considerably lowered. , there is no possibility that the image of the transition part of the dropout will temporarily appear white immediately before the movable contact f of the switching switch SW2 switches to the fixed contact e).

In view of this point, the present invention provides an F that performs inversion prevention signal processing.
In the M-modulated luminance signal processing circuit, signal processing is performed to prevent inversion, which degrades the S/N and waveform characteristics of the luminance signal obtained by selectively outputting the FM-modulated luminance signal, as well as the frequency characteristics of the FM-modulated luminance signal. The purpose of this paper is to propose a method that can perform the same operations as possible, and that also generates less noise on the playback screen during dropout.

:Means for Solving the Problems] The present invention: Recording medium (1) A partially reproduced FM modulated luminance signal is input, and when the FM modulated luminance signal exceeds a predetermined value ○
Based on the first amplitude limiting circuit (7) that limits the amplitude part, the first amplitude limiting circuit (7) suppresses the low frequency human wave number component of the output signal of the first amplitude limiting circuit (7). 7), which has a high-pass single wave generator 19) that returns four signals.
In order to prevent 0 reversal, based on the high frequency emphasis circuit (11) that emphasizes the amplitude of the high frequency component of the FXi variant 11 luminance 1 word reproduced from the recording medium, and a second amplitude limiting circuit (13) that limits a portion of the output signal of the area emphasizing circuit (11) having a predetermined amplitude or more. Based on the output signal of the amplitude detection circuit (5), the output signal of 1 is sent to the first inversion prevention circuit, and the output of 2 is sent to the second inversion prevention circuit, based on the output signal of the amplitude detection circuit (5). A switch circuit SW1 selectively outputs a signal and a demodulation circuit (14) that selectively outputs an output signal of the switch circuit SW based on the switch circuit SW1. When is above a predetermined value, an output signal of 2 is output to the first inversion prevention circuit, and when the level of the FM modulated luminance signal is below a predetermined value, an output signal of 2 is output to the second inversion prevention circuit. It was designed to do so.

[Two effects] According to the present invention described above, when the level of the FM modulated luminance signal is equal to or higher than a predetermined value, the switch circuit S'vV outputs an output signal of 1 to the first inversion prevention circuit, and the FM modulated luminance signal When the level of is equal to or higher than a predetermined value, an output signal of 2 is output to the second inversion prevention circuit.

〔Example〕

Referring to FIG. 1 below, the present invention will be described with reference to FIG.
An example applied to the TR will be explained in detail, but FIGS.
Portions corresponding to those in FIG. 5 are designated by the same reference numerals, and redundant explanation thereof will be omitted. A color video signal recorded on the magnetic r-plane (1) is reproduced by a rotating magnetic head (2). This reproduced color video signal is passed through a reproduction amplifier (3) to a bypass filter (4) 4J'[4], and the bypass filter (4) extracts an FM modulated luminance signal from the reproduced color video signal and sends it to a dropout detector. (5), an adder (6), and a soft limiter (10) to be described later.

K1 is a first anti-inversion circuit, which is composed of an adder (6), a limiter (7), a low-pass filter (8), and a bypass filter (9), as in FIG.

When this first inversion prevention circuit has a frequency of 1, as shown in Figure 2, when the human power level is large, the feedback gain is limited by the limiter (7), so it exhibits flat characteristics, and the input level increases. As it becomes smaller, it has peaking characteristics and the peaking frequency is high band 8mm VT.
In the case of R, it is approximately 10 MHz. Furthermore, since this inversion prevention circuit Kl is a positive feedback circuit, it oscillates when the input level is quite small. The low-pass filtered reproduced FM modulated luminance signal from the low-pass filter (8) is transferred to the switch S
The signal is supplied to the FMti modulation signal circuit (14) via W1 and demodulated.

The demodulated luminance signal from this FM demodulation circuit (14) is de-emphasized! (15), low pass filter (16),
Output terminal T via equalizer (17) and switch SW2. is supplied to K2 is the second inversion prevention circuit, and as in Fig. 5, it includes a soft limiter (10), a booster (high frequency amplifier circuit) (11) and a hard limiter (13).
). This soft limiter (10) lightly limits the level of the reproduced FM modulated luminance signal when it is large, for example.The booster (11) is a linear phase booster with a delay amount of 35 nS (12
), whereby the peak frequency is 13M2, and when the input signal level is above a predetermined level, no boost is performed.)4. A soft limiter (10) boosts the low-level reproduced luminance signal. limiter(
13) strongly limits the level of the reproduced luminance signal from the booster (11).

The reproduced FM modulated luminance signal from the limiter (13) is supplied to the FM demodulator (14) via the switch SW.
demodulated. Demodulation from this FM demodulator (14)! J
The frequency signal is processed by a deninphasis circuit (15), a low-pass filter (16), an equalizer (17):! The output terminal T is output via the optical switch SW2. is supplied to

The dropout detector (;5) is a bypass filter (
For example, −6
6B11 and 2 for 12dB dropout detection
There are two levels. When the level of the FM modulated brightness signal from the bypass filter (4) is higher than 15jB, the movable contact C of the changeover switch SW1 is connected to the 1 constant contact a side, that is, to the first inversion prevention circuit. At the same time, the movable contact f of the changeover switch SW is switched to the constant contact d side, that is, the equalizer (17) side.

Also, when the level of the FM modulated luminance signal from the bypass filter (4) is below -66.B and higher than -12 dB, the movable contact C of the changeover switch SW1 is switched to the fixed contact side,
That is, the second reversal prevention circuit switches to the 2 side, but the movable contact f of the changeover switch SW2 remains switched to the fixed contact d1, that is, the equalizer (17) side.

Furthermore, when the level of the FM modulated luminance signal from the bypass filter (4) is 112 dB or less, selector switch SW
The movable contact C of changeover switch SW2 remains switched to the fixed contact side, that is, the second reversal prevention circuit, but the movable contact f of changeover switch SW2 remains switched to the fixed contact e side, that is, the IH delay device ( 18) remains switched off.

This FM modulated luminance signal processing circuit has the following effects. When the level of the FM modulated luminance signal of the bypass filter (4) is low enough, the 10th inversion prevention circuit
function, the inversion prevention signal processing can be performed without deteriorating the S/N and waveform characteristics of the reproduced luminance signal and the frequency characteristics of the FM modulated luminance signal.

If the level of the FM modulated luminance signal from the bypass filter (4) is quite low, the second inversion prevention circuit functions to further reduce the level of the FM modulated luminance signal and perform dropout compensation. Even when the second
In the reversal prevention circuit 2, the level of the FM modulated luminance signal is too high and is not fixed at the white level, so the movable contact f of the changeover switch SW2 is switched to the fixed contact e, and dropout compensation is performed. The reproduced image of the reproduced luminance signal on the monitor receiver becomes white (
There is no possibility that white noise will occur.

Furthermore, even when the second inversion prevention circuit is functioning, there is almost no deterioration in the S/X or waveform characteristics of the reproduced luminance signal).

The level of the FM modulated luminance signal from the bypass filter (4) is quite low, less than 12 days...
Since mepout compensation is performed, the frequency of dropout compensation is reduced, and the vertical direction of the screen is reduced.
) Compensation can be performed using the video signal.

Thus, according to the above-mentioned FM modulated luminance signal processing circuit, the FM that performs inversion prevention signal processing and dropout compensation
In an M-modulated luminance signal processing circuit, inversion prevention signal processing is performed without deteriorating the S/N and waveform characteristics of the luminance signal obtained by selectively outputting the FM-modulated luminance signal and the frequency characteristics of the FM-modulated luminance signal. At the same time, it is possible to perform dropout compensation using a brightness signal with good correlation, and it is possible to obtain a device with less noise generated on the playback screen during the dropout compensation operation.

2. Effects of the Invention: According to the present invention described above, an FM modulated luminance signal reproduced from a recording medium is inputted, and based on the first amplitude limiting circuit that limits the amplitude portion of the FM modulated luminance signal above a predetermined value, A high-pass i! which suppresses the low frequency component of the output signal of the first amplitude limiting circuit and sweeps it to the input terminal of the first amplitude limiting circuit. a high frequency emphasizing circuit that emphasizes the amplitude of a high frequency component of an FM modulated luminance signal reproduced from a recording medium; an amplitude detection circuit that detects the amplitude of the FM modulated luminance signal based on a second inversion prevention circuit having a second amplitude limiting circuit that limits a portion of the output signal having a predetermined amplitude or more; Based on the output signal of the first inversion prevention circuit,
and a demodulation circuit that selectively outputs the output signal of the switch circuit based on the switch circuit that selectively outputs the output signal of the second inversion prevention circuit, and the switch circuit selectively outputs the output signal of the second inversion prevention circuit. The output signal of the first inversion prevention circuit is output when the level is above a predetermined value, and the output signal of the second inversion prevention circuit is output when the level of the FM modulated luminance signal is below a predetermined value. Therefore, inversion prevention signal processing is performed.
~=1 It is possible to selectively output the modulated luminance signal and custom-order the S/N or waveform of the luminance signal, as well as perform signal processing to prevent inversion that would otherwise degrade the frequency characteristics of the FM modulated luminance signal. In addition to this, it is also possible to obtain less noise on the playback screen during dropouts.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing frequency characteristics of an inversion prevention circuit used to explain the embodiment, and FIGS. 3 to 5 are diagrams showing conventional examples. FIG. K1. 2 is the first and second inversion prevention circuit, (5) is the dropout detector, (6) is the adder, (7) is the limiter, (8) is the low-pass filter, (9) is the bypass filter, ( 10) is a soft limiter, (11) is a booster, (12) is a delay device, (13) is a limiter, (14)
is FM demodulation N, (15) t! f enhancement circuit, (16) halo pass filter, (17) equalizer, (18) IH delay device, SW, and S Vv' 2
are each a switch.

Claims (1)

[Claims] An FM modulated luminance signal reproduced from a recording medium is input,
a first amplitude limiting circuit that limits an amplitude portion of the FM modulated luminance signal above a predetermined value; and a first amplitude limiting circuit that suppresses a low frequency component of an output signal of the first amplitude limiting circuit. a high-pass filter feeding back to the input end;
an inversion prevention circuit; a high-frequency emphasis circuit that emphasizes the amplitude of high-frequency components of the FM modulated luminance signal reproduced from the recording medium; and a portion of the output signal of the high-frequency emphasis circuit that exceeds a predetermined amplitude. Second to do
a second inversion prevention circuit having an amplitude limiting circuit; an amplitude detection circuit for detecting the amplitude of the FM modulated luminance signal; and an output of the first inversion prevention circuit based on the output signal of the amplitude detection circuit. and a switch circuit that selectively outputs the signal and the output signal of the second inversion prevention circuit, and a demodulation circuit that demodulates the output signal of the switch circuit, and the switch circuit is configured to control the level of the FM modulated luminance signal. outputs the output signal of the first inversion prevention circuit when is above a predetermined value, and outputs the output signal of the second inversion prevention circuit when the level of the FM modulated luminance signal is below a predetermined value. An FM modulation luminance signal processing circuit characterized by: