JPS5937788A - Line correlation and dropout compensating 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 a line correlation, drop, and pullout supplementary circuit in a reproducing circuit of a Helica W scan type magnetic recording/reproducing apparatus (hereinafter abbreviated as VTR).

In order to improve the playback quality of VTRs, there are playback circuits equipped with line correlation circuits and video dropout circuits. A line correlation circuit is a 525-bit line that makes up a video signal.
This circuit improves the signal-to-noise ratio by taking advantage of the strong correlation between the signals between each horizontal scanning line (in the case of the NTSC system). In addition, the video dropout and pullout compensation circuit is used to compensate for the loss of video signal due to scratches on the video tape or poor contact with the video head, either before the line period (hereinafter abbreviated as 1H) or before nH (n is an integer). ) is a circuit that replaces missing signals in video signals and prevents image quality deterioration.

A block diagram of a general circuit that combines both circuits is shown in FIG. In the figure, 1 is a magnetic head, 2 is an amplifier equipped with a filter, a limiter, etc., and 3 and 4 are FM
A demodulator demodulates the modulated and recorded signal, 5 is a delay device that delays the line signal, 6 is a limiter, 7 and 8 are subtracters, 9 is an electronic switch, 10 is a dropout detection circuit, 11 is an output terminal It is.

The configuration and operation of the video dropout compensation circuit will be explained below. A video signal that has been FM modulated and recorded on a magnetic tape is demodulated into a video signal B by a demodulator 3 via a magnetic head 1 and an amplifier 2. At the same time, the reproduction FMM cell is delayed by a predetermined time by the delay device 5. The delay time is set equal to the line period (hereinafter abbreviated as 1H). 1H
The delayed FM signal is demodulated into a video signal C in a demodulator 4. The video signal +4B passes through a line correlation circuit, which will be described later, and becomes a video signal at the terminal α of the electronic switch 9.
connected to.

The video signal C is input to the line correlation circuit and is connected to the terminal β of the electronic switch 9. The electronic switch 9 is switched and controlled by a control signal from a dropout detection circuit 10. The dropout detection circuit 10 detects that the signal extracted from the tape is muddy.

This is to detect whether or not a dropout is included. Therefore, this can be a simple envelope detector.

When there is no dropout, the reproducing signal is supplied to the output terminal 11 via the demodulator 3, the line correlation circuit, and the terminal α of the electronic switch 9, as described above.

If a dropout is included, the dropout detection circuit 10 switches the terminals of the electronic switch 9. As a result, while the dropout occurred, the video signal was switched to signal C delayed by 1H, and the electronic switch 9
A signal C is outputted to the output terminal 11 via the terminal β of.

Next, the configuration and operation of the line correlation circuit will be explained. The demodulator 4 and the delay device 5 also serve as a dropout compensation circuit.

The demodulated video signal B contains noise components. Signal components have strong line-to-line correlation, but noise components have no line correlation. Then, in the subtracter 7, subtract the video signal C reproduced before 9IH from the video signal B.
The difference signal (B−C) becomes a noise component. The difference signal is passed through a limiter 6 to remove large amplitude signals, and is subtracted from the video signal B by a subtracter 8.

That is, for small amplitude signals that are not applied to the limiter, the video signal B and the signal 1H before are added by 1A. Therefore, the reproduced signal is restored to be the same as a signal with correlation between lines, but the noise has no correlation and is reduced to one piece of junk. From the above, the S/N improves by 3 dB.

There are two particularly important points in a circuit including such a line correlation circuit and video dropout compensation circuit.

First, the DC level and AC level of the two inputs of the subtracter 7 are made the same. The next step is to make the AC and DC levels of the demodulated signals supplied to the two input terminals α and β of the electronic switch the same. That is, by switching the electronic switch 9, the signal level suddenly changes,
It is important to ensure that these signal changes do not appear as interfering signals.

By the way, in the circuit format shown in FIG. 1, the signal passed through the #+ calculator 8 is connected to the terminal α of the electronic switch 9.
- A signal passed through the demodulator 4 is connected to the terminal β. In this type, even if the DC and AC signal levels are made the same in the subtracter 7 input to the line correlation circuit, since the electronic switches α and β have different circuit types, it is necessary to perform further appropriate level adjustment. For example, use the following method. Separates AC and DC signals,
By regenerating the DC level and adjusting the AC level,
We need to do two things: make the levels the same.

However, in a highly integrated IC circuit, the number of input/output bins is limited, and the above method has the disadvantage of increasing the number of elements and input/output pins.

The present invention has been developed in order to eliminate the drawbacks of the prior art as described above.Therefore, an object of the present invention is to increase the number of elements even in the case of a highly integrated IC circuit. An object of the present invention is to provide a line correlation and dropout compensation circuit that prevents signal level changes from occurring during signal switching without increasing the number of input/output pins.

In order to achieve the above object, the present invention minimizes the number of signal level adjustment points by devising the connection position of the signal changeover switch in a playback circuit equipped with a one-line correlation circuit and a video dropout compensation circuit. It is something.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a diagram showing an embodiment of the present invention. The circuit configuration shown in this figure differs from that in FIG. 1 in the position of the electronic switch 9, and other components are the same.

First, the operation of the video dropout compensation circuit will be explained.

A video signal that has been FM modulated and recorded on a magnetic tape is demodulated into a video signal BK through an amplifier 2 and a demodulator 6, and is delivered to a terminal α of an electronic switch 9. On the other hand, delay device 5 and demodulator 4
The video signal C from 1H before reaches the terminal β of the electronic switch 9. When there is no dropout, the video signal B is applied to the output terminal 11 via the electronic switch 9 and the subtractor 8.

If dropout or dropout is included, the dropout detection circuit 10 switches the terminal of the electronic switch 9 to the β side. Then, a video signal with line correlation from 1H before is supplied to the output terminal 11.

What should be noted about the present invention is that the terminals α and β of the electronic switch 9 are located after the demodulator 3 and the demodulator 4.

In the conventional system, as shown in FIG. 1, a subtracter 8 is inserted between the terminal α of the electronic switch 9 and the demodulator 3, so that the levels of the demodulated signals supplied to the two input terminals are different.

As a result, in order to make the AC voltage level and the DC voltage level the same, it was necessary to adjust the signal levels at the input of the subtracter 7 and at the inputs α and β of the electronic switch.

However, according to the present invention, each terminal of the electronic switch is located after the demodulator, so if the AC level and DC level are adjusted by the input of the subtracter 7, the adjustment by the input of the electronic switch can be done at the same time. can be done. In other words, common adjustments can be made. Furthermore, the conventional method has the disadvantage that the number of pins increases by two compared to the circuit type of the present invention.

Next, the operation of the line correlation circuit will be explained. The demodulator 6.4 and delay device 5 also serve as a dropout and pullout compensation circuit.

Video signal C delayed by 1H is subtracted from video signal B demodulated by subtracter 7, and the difference signal (B-C) becomes a noise component.

This difference signal is passed through a limiter 6. Then, the subtracter 8 subtracts it from the video signal. The video signal to be subtracted here is the B signal if there is no dropout or dropout, but it is the C signal if there is a dropout. In other words, mud.

When a pullout occurs, there is no effect of line correlation, and 3/1'
Degrades J.

However, the period during which dripping and dropout occur is on the order of 10 .mu.sec, and even if deterioration occurs during this period, there is no practical problem at all.

A part of an actual circuit diagram of the present invention is shown in FIG.

Figure 3 shows limiter 6, subtracters 7 and 8, and electronic switch 9.
, its input terminals α and β, its output terminal 11, and switching control terminals 12 and 16 of the electronic switch 9 are shown. Further, 14 and 15 are input pins of the integrated circuit, and 14 is inputted with a video signal from 1H ago, and 15 is inputted with a current video signal. 14
Needless to say, the AC input levels of and 15 are adjusted in advance.

As described above, according to the present invention, in a reproducing circuit equipped with a line correlation circuit, a video dropout compensation circuit, and a drop-out compensation circuit, the adjustment bm of the signal level is minimized, and the signal level does not change when switching signals. It is possible to switch. Furthermore, by integrating this circuit, it is possible to reduce the number of parts and the number of input/output pins.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional reproducing circuit equipped with a line correlation circuit and a video dropout compensation circuit, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. FIG. 2 is a specific circuit diagram showing an example.

Claims (1)

[Claims] 1. A first demodulation circuit that demodulates a regenerator, and a second demodulation circuit that inputs and demodulates the reproduced signal after delaying the reproduced signal by a predetermined time using a delay circuit. circuit, a detection circuit for detecting dropout in the reproduced signal, and an output terminal of the first demodulation circuit connected to one input terminal of the second demodulation circuit;
The output of the demodulation circuit is connected to the other input terminal K. switching means for selecting and outputting one of them based on the output of the detection circuit; and a first subtracter for extracting a difference component between the output of the first demodulation circuit and the output of the second demodulation circuit. and a second subtracter that limits the extracted difference component by limiting and then takes out the difference component between this and the output of the switching means. and dropout compensation circuit.