JPH03192571A - magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To eliminate erroneous detection by providing a circuit for expanding an amplitude during a period of synchronizing signal of a video signal, an FM modulating circuit having its enough linearity, an AM detecting circuit and a circuit for separating the synchronizing signal in comparison between its amplitude and a reference value. CONSTITUTION:The video signal with the synchronizing signal expanded in amplitude is obtained by the synchronizing signal expanding circuit 2, and is FM modulated by the FM modulating circuit 5 having enough linearity via a preemphasis circuit 4 and then recorded on a magnetic tape 8. The regenerative signal is sent to the deemphasis circuit 12, and simultaneously an envelope of the regenerative FM signal is detected by the AM detecting circuit 13, and is sent to the regenerative synchronization separating circuit 14 composed of a comparator, where the synchronizing signal at a larger envelope level than a reference value is detected. Now, if a drop-out is generated, the envelope level is diminished, and a comparator is not in excess of the reference value, so that the erroneous detection by taking the synchronizing signal for the regenerative signal does not take place at all.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for reducing the adverse effect on a reproduced signal caused by medium defects such as dropouts in a recording/reproducing apparatus.

[Conventional technology]

FIG. 17 is a block diagram of a video tape recorder, which is an example of a conventional recording/reproducing device, in which (1) is a clamp circuit that fixes the synchronization end of the video signal to a predetermined potential; (4)
is a pre-emphasis circuit that emphasizes the high range of the video signal (
5) is an FM modulation circuit that performs FM modulation on the video signal output from the pre-emphasis circuit; (6) is a recording amplifier that amplifies the output of the FM modulation circuit; (7) is a head that performs recording and reproduction;
(8) is a magnetic tape which is a recording medium.

(9) is a head amplifier that amplifies the reproduction voltage generated in the head (7) during reproduction, (10) is an FM demodulation circuit that demodulates the output of the head amplifier (9), and (11) is an FM demodulation circuit (10). ) is a low-pass filter that passes only the video signal from the output of the pre-emphasis circuit (Step 2).
This is a de-emphasis circuit that attenuates and restores the high frequencies emphasized in step 2).

Next, the operation will be explained using FIGS. 17 to 22. In Figure 17, the video signal manually input during recording is
As shown in FIG. 18, the clamp circuit (1) fixes the synchronization tip to a predetermined potential i:5y(v), and then the pre-emphasis circuit (4) emphasizes the high frequency range.

The next FM modulation circuit (5) has the input voltage vs. oscillation frequency characteristic shown in FIG. 19, so it oscillates at a frequency corresponding to the potential of the video signal, and f! lYI, black level oscillates fa1, white level fw oscillates. FM modulation circuit (
The output signal of 5) is amplified by the recording amplifier (6) and applied to the head (7) to become a recording current, which is then applied to the magnetic tape (8).
) the signal is recorded.

Next, the reproduced FM signal generated in the head (7) during reproduction is amplified by the head amplifier (9), and the FM demodulation circuit (1) is amplified by the head amplifier (9).
0). Since the FM demodulation circuit (10) has the frequency versus voltage characteristic shown in FIG. 1
Step 1) removes unnecessary signal components, and the de-emphasis circuit (step 2) attenuates high frequencies to obtain the original video signal.

[Problem to be solved by the invention]

Conventional recording and reproducing devices are configured as described above, so when dropout occurs due to scratches on the surface of the magnetic tape, the reproduced FM signal becomes constricted as shown in Figure 21, which makes it seem like the signal is low. This is the same as if the frequency signal were input to the FM demodulation circuit, and the reproduced video signal drops to a potential much lower than the synchronization tip as shown in FIG.

On the other hand, a video tape recorder, which is a magnetic recording and reproducing device, detects the synchronization signal interval, corrects the time axis, and re-attachs the synchronization signal to the correct position. Some devices have a time base corrector, but in the case of this device, if the playback video signal when a dropout occurs is mistakenly detected as a synchronization signal, the time base correction operation cannot be performed normally, and the playback image The problem was that it became unstable.

This invention was made in order to solve the above-mentioned problems, and its purpose is to provide a magnetic recording and reproducing device that can accurately separate only the synchronization signal and that can obtain stable reproduced video signals. do.

[Means and operations for solving the problem] The magnetic recording/reproducing device according to the invention of claim 1 includes a synchronization signal expansion circuit that expands the amplitude of the synchronization signal, and sufficient linearity at least up to the tip of the expanded synchronization signal. The present invention is characterized in that it is provided with an FM modulation circuit having the following: and a reproduction synchronization separation circuit that compares the reproduction FM signal amplitude obtained during reproduction with a reference value and separates a synchronization signal.

In the invention of claim 1, a signal of a frequency that can be reproduced with a relatively large amplitude during reproduction is recorded during the synchronization period, and the reproduction F
Since only the case where the M signal amplitude is larger than the reference value is detected as a synchronization signal, there is no possibility that a case where the reproduced FM signal amplitude becomes small at the time of dropout is mistakenly detected as a synchronization signal.

The magnetic recording and reproducing device according to the invention of claim 2 includes an offset voltage applying circuit that applies an offset voltage to the FM modulation circuit during a synchronization period to shift the oscillation frequency to a lower frequency range, and a reproduction FM signal amplitude obtained during reproduction that is set to a reference value. This is characterized by the provision of a reproduction synchronization separation circuit that separates the synchronization signal.

In the invention of claim 2, a signal of a frequency that can be reproduced with a relatively large amplitude during reproduction is recorded during the synchronization period, and the reproduction F
Since only the case where the M signal amplitude is larger than the reference value is detected as a synchronization signal, there is no possibility that a case where the reproduced FM signal amplitude becomes small at the time of dropout is mistakenly detected as a synchronization signal.

The magnetic recording and reproducing device according to the invention of claim 3 includes: an oscillation circuit that oscillates at at least two different frequencies in a synchronization period and other periods; a multiplier that multiplies an FM modulation circuit output and an oscillation circuit output; This device is characterized in that it includes a reproduction synchronization separation circuit that compares the signal amplitude with a reference value and separates the synchronization signal.

In the invention according to claim 3, a signal of a frequency that can be reproduced with a relatively large amplitude during reproduction is recorded during the synchronization period, and the reproduction F.
Since only the case where the M signal amplitude is larger than the reference value is detected as a synchronization signal, there is no possibility that a case where the reproduced FM signal amplitude becomes small at the time of dropout is mistakenly detected as a synchronization signal.

The magnetic recording and reproducing device according to the invention of claim 4 includes an oscillation circuit that oscillates at a frequency lower than the carrier frequency of the FM signal corresponding to the synchronization tip, and a switch circuit that switches the FM signal to the output signal of the oscillation circuit during the synchronization period. The present invention is characterized in that it includes a reproduction synchronization separation circuit that compares the reproduction FM signal amplitude obtained during reproduction with a reference value and separates a synchronization signal.

In the invention of claim 4, a signal of a frequency that can be reproduced with a relatively large amplitude during reproduction is recorded during the synchronization period, and the reproduction F.
Since only the case where the M signal amplitude is larger than the reference value is detected as a synchronization signal, there is no possibility that a case where the reproduced FM signal amplitude becomes small at the time of dropout is mistakenly detected as a synchronization signal.

[Embodiments of the invention]

An embodiment of the invention according to claim 1 will be described below with reference to FIGS. 1 to 7. FIG. 1 is a block circuit diagram of this embodiment, and the differences from the conventional example will be explained below.

(2) is a synchronization signal expansion circuit, and recording synchronization separation circuit (3)
The amplitude of the synchronization signal is expanded based on the output signal of. (
13) is an AM detection circuit that detects the envelope of the reproduced FM signal obtained during reproduction, and (14) is a reproduction synchronization separation circuit that compares the output of the AM detection circuit (13) with a reference value and separates the synchronization signal.

Next, the operation will be explained. Figure 2 is a block circuit diagram showing an example of the configuration of the synchronization signal expansion circuit (2).
is an A/D converter, (2B) is an I'LOM, (27) is a data selector, and (28) is a D/A converter.

First, the video signal input during recording is sent to an A/D converter (2
5) A/D conversion is performed. The synchronization signal is then switched by the data selector (27) to the output data of the ROM (26), which stores the data of the synchronization signal with a large amplitude, and is D/A converted by the D/A converter (28). A video signal in which the amplitude of the synchronizing signal is expanded as shown in FIG. 3 is obtained. This video signal passes through a pre-emphasis circuit (4) and then passes through an FM modulation circuit (5) with sufficient linearity.
is FM modulated. The spectrum of this FM modulation wave is
As shown in Figure 4, the frequencies corresponding to the black level and white level are the same as in the conventional example, but the frequency corresponding to the synchronization tip is lower than in the conventional example, and the pre-emphasis circuit (
f lY2, which is a lower frequency than the tip of the undershoot caused by 4). This FM signal is amplified by a recording amplifier (6) and recorded on a magnetic tape (8).

On the other hand, the frequency characteristic of the reproduction output of the head (7) is 145
As shown in the figure, the differential characteristic increases with frequency, but above a certain frequency it decreases due to various loss factors such as spacing loss.Therefore, the gain in the output of the head amplifier (9) increases. As shown in FIG. 6(b), the reproduced FM signal has the highest synchronization tip level with the lowest frequency, and then decreases in the order of black level and white level. The reproduced FM signal is sent to an FM demodulation circuit (10), a low-pass filter (11), and a de-emphasis circuit (12), as well as to an AM detection circuit (13), as in the conventional example.

The AM detection circuit (13) detects the envelope of the reproduced FM signal (Fig. 6 (C)), and then sends it to the reproduction synchronization separation circuit (14) consisting of a comparator, where the envelope level is determined. A sync signal portion larger than the reference value E*** (V) is detected (FIG. 6(d)). Here, if a dropout as shown in Figure 7(b) occurs, the envelope level becomes small as shown in Figure 7(C), and the reference value of the comparator E REIP (V
), there is no possibility that it will be mistakenly detected as a synchronization signal.

In the above embodiment, the output of the head amplifier (9) is directly input to the AM detection circuit (13), but as shown in FIG. AM
If the configuration is such that it is provided before the detection circuit (13) and strengthens the difference in amplitude #N depending on the frequency of the reproduced FM signal, the synchronization signal detection accuracy can be further improved.

Next, an embodiment of the invention of claim 2 is shown in FIGS. 11 to 13.
This will be explained using figures. FIG. 11 is a block circuit diagram of this embodiment, and the differences from the embodiment shown in FIG. 1 will be explained below.

(15) is an offset voltage application circuit that generates an offset voltage based on the output signal of the recording synchronization separation circuit (3), and the offset voltage output is connected to the offset voltage input terminal of the FM modulation circuit (5).

Next, the operation will be explained. The video signal input during recording is passed through the clamp circuit (1), pre-emphasis circuit (
2) and is input to the FM modulation circuit (3).

FIG. 12 is a circuit diagram showing a specific example of the offset voltage application circuit (16). Power supply voltage +V with resistor R1 and resistor R2
cc is divided into voltages, and its contact point a is connected to resistor R5 and transistor T.
11 to ground, and the transistor Trl
A base resistor R4 is connected to the base of . When a recording synchronization signal (FIG. 13(a)) is applied to the base of the transistor Trl through the base resistor R4, the transistor T becomes conductive only during the synchronization signal period, and the resistor R3 is connected to the resistor R2.
are connected in parallel, so the voltage at contact a decreases.

This voltage is applied to the offset voltage input terminal of the FM modulation circuit (5). As a result, the spectrum of the FM signal output from the FM modulation circuit (5) becomes similar to that shown in FIG.

Therefore, the same effect as the embodiment of the invention of claim 1 shown in FIG. 1 can be obtained.

Next, an embodiment of the invention according to claim 3 will be described using FIG. 14 and FIG. 15. FIG. 14 is a block diagram of this embodiment, and the differences from the embodiment shown in FIG. 1 will be explained below.

(17) is an inverting amplifier that inverts the polarity of the video signal, (!
Reference numeral 9) is an oscillation circuit that oscillates at at least two different frequencies between the synchronization signal period and other periods based on the output signal of the recording synchronization separation circuit (3). (18) is a multiplier that multiplies the output of the FM modulation circuit (5) and the output of the oscillation circuit (19). The output of the multiplier (18) is input to the recording amplifier (6) via a low-pass filter (20).

Next, the operation will be explained. The video signal input during recording is passed through the clamp circuit (1), pre-emphasis circuit (
4) and inverse amplification! ! ! (17) and is input to the FM modulation circuit (5). The modulation sensitivity of this FM modulation circuit (5) is similar to that of the conventional example, but the center frequency is selected to be high. Furthermore, since the polarity of the input video signal is inverted, the spectrum of the output FM signal has a high synchronization tip level frequency fWY, as shown in Figure 15.
The next lowest level is the black level fa and the white level fw'.

The oscillation circuit (19) sends out a signal with a frequency of Δf-d during the synchronization signal period and Δf during periods other than the synchronization signal period. Here, Δf is Δf=fa”+fa or Δf=fw”+
It is fw.

Next, the multiplier (18) multiplies the output of the FM modulation circuit (5) and the output of the oscillation circuit (19), and the frequency difference and sum components are output. The FM signal component shifted to the lower frequency range of this signal is extracted by a low-pass filter (20). The spectrum of this FM signal is similar to that shown in FIG. Therefore, the same effect as the embodiment of the invention of claim 1 shown in FIG. 1 can be obtained.

Next, an embodiment of the invention according to claim 4 will be described using the block circuit diagram of FIG. 16. Hereinafter, points different from the embodiment shown in FIG. 1 will be explained.

(21) is an oscillation circuit, and the carrier wave frequency f of the FM signal corresponding to the synchronization tip is f! Frequency f lower than Yl ff1Y2
oscillates. (22) is a switch circuit which switches the output of the FM modulation circuit (5) and the output of the oscillation circuit (21) based on the output signal of the recording synchronization separation circuit (3), and supplies it to the recording amplifier (6).

Next, the operation will be explained. The video signal input during recording is passed through the clamp circuit (1), pre-emphasis circuit (
4), the FM modulation circuit (5) converts F as in the conventional example.
M modulated. The switch circuit (22) switches the output of the FM modulation circuit (5) to the output of the oscillation circuit (21) only during the synchronization signal period. As a result, the spectrum becomes similar to that shown in FIG. Therefore, the same effect as the embodiment of the invention of claim 1 shown in FIG. 1 can be obtained.

〔Effect of the invention〕

As described above, the inventions of claims 1 to 4 provide for, at the time of recording,
If the frequency corresponding to the synchronization tip of the FM modulated video signal is lower than the preshoot tip of the video signal generated by the pre-emphasis circuit, and the reproduced FM signal amplitude is larger than the reference value during playback. Since it is configured to detect only the small amplitude of the reproduced FM signal as a synchronization signal, there is no possibility that the lid part where the amplitude of the reproduced FM signal is small will be mistakenly detected as a synchronization signal at the time of dropout, and a stable reproduced video signal can be obtained. effective.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing an embodiment of the invention of claim 1, FIG. 2 is a block circuit diagram of a synchronization signal expansion circuit in this embodiment, and FIG. 3 explains the operation of this synchronization signal expansion circuit. Figure 4 is a spectrum diagram for explaining the operation of this embodiment, Figure 5 is a characteristic diagram of the head of this embodiment, and Figures 6 and 7 are reproduction diagrams of this embodiment. A signal waveform diagram for explaining the operation of the synchronization separation circuit, FIG. 8 is a block circuit diagram of a reproduction system of another embodiment of the invention of claim 1, and FIG. 9 is a characteristic of the synchronization signal emphasizing circuit in this embodiment. Similarly, FIG. 10 is a characteristic diagram of another example of this synchronization signal emphasizing circuit, FIG. 11 is a block circuit diagram of an embodiment of the invention according to claim 2, and FIG. 12 is an offset voltage application circuit of this embodiment. FIG. 13 is a signal waveform diagram for explaining the operation of this offset voltage application circuit, FIG. 14 is a block circuit diagram of an embodiment of the invention according to claim 3, and FIG. FIG. 16 is a block circuit diagram of an embodiment of the invention of claim 4, FIG. 17 is a block circuit diagram of a conventional magnetic recording/reproducing device, and FIG. 18 is a diagram of the output signal spectrum of the multiplier of the embodiment. A signal waveform diagram for explaining the operation of the clamp circuit in the example, FIG. 19 is a modulation characteristic diagram of the FM modulation circuit of this conventional example, FIG. 20 is a demodulation characteristic diagram of the FM demodulation circuit of this conventional example, and FIG. 21 and the 22nd
The figure is a signal waveform diagram for explaining the problems of the conventional example. (1)... Clamp circuit, (2)... Synchronization signal expansion circuit, (3)... Recording synchronization signal separation circuit, (4
)...Pre-emphasis circuit, (5)...FM modulation circuit, (7)...head, (8)...magnetic tape, (10)...FM demodulation circuit, (rt),
(20)...Low pass filter, (12)...De-emphasis circuit, (13)...AM detection circuit, (1
4)... Regeneration synchronization separation circuit, (15)... Synchronization emphasis circuit, (1B)... Offset voltage application circuit, (17
)--inverting amplifier, (18)... multiplier, (19
), (21)...Oscillation circuit, (22)...Switch circuit. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (4)

[Claims] (1) In a magnetic recording and reproducing device that FM modulates a video signal having a negative polarity synchronization signal, records it on a recording medium, demodulates it, and reproduces it, a synchronization signal expansion circuit that extends the amplitude of the synchronization signal period of the FM video signal. , an FM modulation circuit that has sufficient linearity up to the tip of this expanded synchronization signal, an AM detection circuit that performs AM detection on the reproduced FM video signal, and a synchronization signal that is separated by comparing the amplitude of this AM detection signal with a reference value. What is claimed is: 1. A magnetic recording/reproducing device comprising: a reproduction synchronization separation circuit. (2) In a magnetic recording/reproducing device that FM-modulates a video signal with a negative polarity synchronization signal, records it on a recording medium, demodulates it, and reproduces it, an offset voltage is applied to the FM modulation circuit only during the synchronization signal period to change the oscillation frequency. It is equipped with an offset voltage application circuit that shifts to the reduction side, an AM detection circuit that performs AM detection on the reproduced FM video signal, and a reproduction synchronization separation circuit that compares the amplitude of this AM detection signal with a reference value and separates the synchronization signal. A magnetic recording/reproducing device characterized by: (3) In a magnetic recording and reproducing device that FM-modulates a video signal with a negative polarity synchronization signal, records it on a recording medium, demodulates it, and reproduces it, the synchronization signal period of the FM video signal and the other periods have different frequencies. an oscillation circuit that generates a signal; a multiplier that multiplies the output of this oscillation circuit and an FM video signal;
A magnetic recording/reproducing device comprising: an AM detection circuit that performs AM detection on a reproduced FM video signal; and a reproduction synchronization separation circuit that compares the amplitude of the AM detection signal with a reference value and separates a synchronization signal. (4) In a magnetic recording and reproducing device that FM-modulates a video signal with a negative polarity synchronization signal, records it on a recording medium, demodulates it, and reproduces it, a video signal with a frequency lower than the carrier frequency corresponding to the synchronization tip of the FM video signal is used. an oscillation circuit that generates a signal;
A switch circuit that replaces the output signal of this oscillation circuit with the synchronization signal period of the FM video signal, an AM detection circuit that performs AM detection on the reproduced FM video signal, and a synchronization signal that compares the amplitude of this AM detection signal with a reference value. A magnetic recording/reproducing device comprising: a reproduction synchronization separation circuit for separating.