JPS6094585A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To decrease the noise bar caused at the time of the search in VTR by inserting the filter limiting the band to the rear of the limiter in order to remove the amplitude variation. CONSTITUTION:The luminance FM signal, which is reproduced from the magnetic tape and is processed by the reproducing equivalent circuit, AGC, etc., is inputted to the terminal 51. The filter 54 limiting the band is inserted to the rear of the inversion prevention circuit 15 connected to the terminal 51 and the limiter 52 removing the amplitude variation. The white jump of the noise bar caused at the time of the search is set to the gray level by inserting the filter 54. In this way, the reproduction picture, which is hard to see the noise visually, can be obtained. As such, the noise bar caused at the time of the search in VTR can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Subject of the Invention] The present invention relates to a magnetic recording/reproducing device that angle-modulates a video signal and records it on a magnetic medium, and particularly relates to a video signal processing circuit suitable for reducing noise bars during a search. .

[Background of the invention]

When performing double-speed playback on a VTRK, it is necessary to play across a guard band or a reverse azimuth recording track, and noise on the screen appears in proportion to the speed.

FIG. 1 is a diagram showing the configuration of a conventional V'l'H regeneration processing circuit. In Figure 1, 1 is a magnetic tape, 2 is a video head, and 3 is a rotary transformer.

4.5 is a preamplifier, and 6 and 7 are feedback resistors.

The resonance in the first stage of the preamplifier is sufficiently damped, and the amplitude characteristics are made approximately flat. 8 is the switch f7/amplifier, 9//i head switch pulse input terminal, 10 is the bass amplifier, 11 is the HPF for extracting the FM luminance signal (YFM), 12 is the reproduction FM equalizer, and 13 is the two head output signals. 14 is a YFM level detector, 15 is an inversion suppression circuit that defines the input level, 16 is a dropout detection circuit, and 17 is a signal 1H before dropout. Dropout compensation circuit replaced with 18 is a limiter, 1
9 is an FM demodulator, and 20 is an LPF for spurious removal.

21 is a main de-emphasis circuit, 22 is a dynamic de-emphasis circuit, and 23 is a noise cancellation circuit that suppresses high-frequency, small-amplitude signals.

24 is a circuit that mixes the luminance signal and chroma signal, and 25 is a circuit B that extracts only the chroma signal from the playback signal from the tape.
PF, 26u AGO amplifier for adjusting the levels of the color burst signals output from the two heads to a constant value, and 27 is a converter for returning the chroma subcarrier to 3.58MHz.

28 #i conversion carrier generating circuit, 29 BPF for spurious removal, 50 comb filter for crosstalk removal, 31 dynamic de-emphasis D path +
32 t=t + force 2-burst level A detector, 55
A burst de-emphasis circuit compresses only the fi burst signal by 6 dB, and 34 is a video signal output terminal. 1st
The configuration of the playback signal processing circuit shown in the figure is common, but the problem in Figure 1 is that the same playback processing is performed during normal playback and search (double speed playback), so a noise bar appears on the screen during search. It is to come. Noise during search is generated due to reproduction across the guard band or reverse azimuth recording track. Yes, Fi when searching
Amplitude fluctuations occur in the Mitsuield in proportion to the speed, and even if the amplitude fluctuations are removed with a limiter, the fluctuations are to such an extent that normal image quality cannot be obtained, resulting in noise. Furthermore, there is a lot of noise.

If the amplitude level is small, the effect of the inversion prevention circuit 15 is weakened, and an inversion phenomenon occurs, which together with noise degrades the image quality over a wide range on the screen.

Here, the reproduction equivalent circuit 12 normally has a peak of f4v+ at the white peak frequency in order to compensate for the drop in high frequency components that occur during the recording and reproduction process. Therefore, the noise component at the time of search also has the f characteristic of the reproduction equivalent circuit 12, and the noise bar becomes more noticeable on the screen as a blown-out image. By setting the noise bar to a gray level that causes overexposure, the noise bar becomes less noticeable on the screen. As one method, when searching, f% of the reproduction equivalent circuit 12 is set to the luminance FM to gray out the noise.
However, even if the noise bar can be grayed out by the above method, an inversion phenomenon occurs on the entire screen as a side effect, making it ineffective.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a video signal processing circuit that eliminates the drawbacks of the prior art, suppresses the inversion phenomenon that occurs during a search, and achieves a stable image with less visible noise using a very simple circuit.

[Summary of the Invention] In order to visually reduce search noise, which is a conventional problem, the present invention inserts a filter after a limiter for removing amplitude fluctuations, suppresses the inversion phenomenon caused by a decrease in the amplitude level, and Busy, set the noise bar's overexposure to gray level.

[Embodiment of the Invention] An embodiment of the present invention is shown in FIG. 51 in Figure 2
#i Equivalent circuit for playing back from magnetic tape.

Input terminal for luminance FM signal that has undergone multiple processing such as AGO,
52 and 53 are limiters that remove amplitude fluctuation components.

54 is a band-limiting filter, 55 is an output terminal for a demodulated luminance signal, and the other circuits are the same as those shown in FIG.

A feature of FIG. 2 is that a filter 54 is provided after the limiter 52. As mentioned above, if the same processing as during normal playback is performed during busy search, f of the playback equivalent circuit 12
The particular peak is at a slightly higher frequency than the white level (
For example, the allocageron of FM signal is 4.2 to 5.4 M.
If the frequency is about 6 MHz), the noise component also has the f characteristic of the reproduction equivalent circuit 12. Therefore, the noise bar during the search becomes more noticeable on the screen due to overexposure. In order to make this noise bar less noticeable, K should be set to a noise bar gray level. For this reason, the limiter 52
The filter 54 provided after the search ML/
Set the isband to gray level.

The solid line in FIG. 3 shows the specific frequency characteristics of the filter 54 in FIG. 2. The f characteristic in FIG. 3 has a peak near the gray level frequency of the luminance FM signal. Here, it is important to determine the f% of the filter 54. For example, F
M signal allocageron is 4.2MHz with sync step
, If the white peak is 5.4MHz, then the f characteristic of the reproduction equivalent circuit 12 is.

It is set to have a peak point at 6 MHz as shown by the dotted line. Therefore, the peaking frequency of the filter 54 is selected to be lower than the peaking frequency of the regenerative equivalent circuit 12. Tsuma, 9. FM signal allocation range is 4.2-5
．． If the frequency is 4 MHz, the frequency corresponding to the gray level of the luminance signal will be 5 MHz, and if the characteristics of the filter 54 are set as shown in FIG.

The noise bar when searching can be set to gray level 1
The noise bar on the screen becomes difficult to see.

The position of the filter 54 is also important. The filter 54 is connected to the inversion prevention circuit 1 in order to obtain a noise bar gray level.
5, the level of the lower sideband of the reproduced FM signal is raised, causing a loop inversion phenomenon and degrading the image quality. therefore.

The position of the filter 54 is the inversion prevention circuit 15. It must be provided after the limiter 52.

Furthermore, it is also effective in suppressing an inversion phenomenon caused by a decrease in signal level during the filter 54#'i search. When searching, the amplitude of the signal fluctuates in proportion to the search speed.
If the level drops significantly, the noise bar will appear as described above, but even if it is a noise bar, the amplitude level will drop and there will be places where inversion is likely to occur. Therefore, the effect of the inversion prevention circuit 15 cannot be exerted, and the limiter 52 restores the high-frequency sideband even for low-level signals, and the filter 54 is provided afterwards to prevent inversion from occurring.

In addition, in FIG. 2, the dropout compensation circuit 17 includes a limiter 52. Although it is installed after the filter 54, %
It is not limited to IC.

FIG. 4 shows nine embodiments of the present invention using a specific circuit. Fourth
In the figure, 101 is the input terminal of the limiter, 1o2 is the output terminal of the limiter, and 6. It is an rc pin terminal. 1
Q5Fi is the input terminal to the dropout compensation circuit after the filter, and fi is the pin terminal of the IC. 104 is resistance,
1o5 is an inductor, 1o6 is a capacitor, hb, 10
4.105.1015 constitutes a filter. 10
7 is a transistor that turns the filter into 011110FF, 1
08 is an input terminal for a signal that controls the dropout compensation circuit, 1o9 is an output terminal of the dropout compensation circuit, 11
0 is an input terminal for a dropout compensation signal delayed by 1H, and 111 is an input terminal for a signal that controls the transistor 107.

The constants shown in FIG. 4 are a specific example for realizing the filter characteristics shown in FIG. 3. tg4 diagram busy, transistor 10
When 7 is OFF, the filter does not operate and signals are directly transferred from terminal 102 to terminal 103.

When a signal is input from the K11III control signal input terminal 111 during a search, the transistor 107 is turned on and the resistor 104.
Inductor 105. A filter such as the capacitor IQ6 is turned on, filters the limited signal output from the output terminal 102, and inputs it to the 9th order dropout compensation circuit.

As described above, by performing the filtering after the limiter, it is possible to make the noise at the time of Rusate less visible on the screen.

Here, R#i provided in the L and GK differential rows has an important meaning. A transistor is used to turn on and off the filter 54.
Using switch flQ7 is also a method with good cost performance. however.

The use of transistor switches poses problems during normal playback. Jamari 9 Busy Tran during normal playback') y, fi
107 OFF I However, there is a stray capacitance between the collector and emitter of the transistor, which causes some traps near the peaking frequency of the filter during normal reproduction. R, which is provided with parallel tabs to L and CK, suppresses the occurrence of this trap. If R is small, the amount of traps that occur during normal reproduction is large, and when the signal is played back, the peaking OQ becomes small and the noise reduction effect is weakened. If R is too large, Q is too large and the band is limited, degrading the image quality. Therefore, the magnitude of R is selected based on the ratio to the load impedance, and for example, if RL=I KΩ, it is best to select it to be about 5.6Ω.

〔Effect of the invention〕

According to the present invention, by setting the noise bar generated during a search to a gray level, it is possible to realize a reproduced image in which the noise visually appears. Furthermore, the 5 reversal phenomenon that is particularly likely to occur in the search is greatly reduced.

The present invention can realize the above effects with a very simple circuit, and can provide a high-temperature noise bar suppression circuit with good cost performance.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of a conventional example, and Figure 2 is a block diagram showing the configuration of a conventional example.
FIG. 3 is a block diagram showing an embodiment of the present invention, FIG. 3 is a diagram showing specific frequency characteristics of the present invention, and FIG. 4 is a diagram showing a specific circuit in the present invention. Explanation of symbols 1...Magnetic tape, 2...Magnetic head. 15... Inversion prevention circuit, 17... Dropout compensation circuit. 19... Demodulation circuit, 52... Limiter, 54... Filter. 104...Resistor, 105...Inductor, 106...
・Capacitor, 107 ・Transistor, 111・
...Search control signal input terminal Fig. 2/6 Fig. 3 Fig. 4

Claims (1)

[Claims] 1. Equipped with a video head for reading video signals recorded on a magnetic medium and a preamplifier connected to the video head,
In a magnetic recording/reproducing apparatus, the signal read out by the video head is a re-modulated video signal, and the magnetic recording/reproducing device includes at least an amplitude limiter for removing an amplitude fluctuation component of the angle-modulated video signal. A video signal processing circuit characterized in that it is later equipped with a band limiting circuit.