JPH03250459A - Magnetic recording and reproducing device - 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 (Field of Industrial Application) The present invention relates to a magnetic recording/reproducing device that performs FM modulation on a video signal to record/reproduce it, and more particularly to a circuit for suppressing an inversion phenomenon that occurs during reproduction.

(Prior Art) FIG. 8 is a block circuit diagram showing the recording and reproducing system configuration of a conventional magnetic recording and reproducing device, such as a video tape recorder. , (2) is the FM modulation circuit, (3) is the F
a recording amplifier that amplifies the output signal of the M modulation circuit (2);
(4) is a recording/reproducing head, (5) is a magnetic tape,
(6) is a regenerative amplifier that amplifies the reproduced FM signal; (7)
is a reproduction equalizer circuit that corrects the frequency characteristics of the reproduction FM signal output from the reproduction amplifier (6), and (8) is the FM
Demodulation circuit (9) is a de-emphasis circuit that attenuates the high-frequency components of the video signal emphasized during recording (lO)
1 is a dropout detection circuit that detects dropouts from the output reproduction FM signal of the reproduction equalizer circuit (7);
1) I delays the reproduced video signal by one horizontal period (IH)
H delay circuit (12) is a switch circuit.

FIG. 9 is a circuit diagram showing an example of the configuration of the dropout detection circuit (10), which includes a diode D1, a capacitor C1, and a resistor R.
1. It is composed of a variable resistor VRI and a comparator (17), and an envelope detection circuit (16) is composed of a diode D1, a capacitor C1, and a resistor R1.

Next, the operation will be explained.

During recording, the high-frequency components of the input video signal are emphasized by the brilliance emphasis circuit (1) (see Figure 10 (a)), FM modulated by the FM modulation circuit (2), and then sent to the recording amplifier (
3), and the magnetic tape (5) is amplified by the head (4).
) recorded above.

During reproduction, the FM modulated video signal read from the magnetic tape (5) by the head (4) is amplified by the reproduction amplifier (6). At this time, the lower sideband of the reproduced FM signal is emphasized and the upper sideband is suppressed, causing the modulation index to change. At the same time, an imbalance of sidebands occurs, and the high-frequency components are emphasized by the pre-emphasis circuit (1). The part corresponding to the rising edge of the video signal (see Figure 10(a)) is 's10.
As shown in Figure (b), there is a large constriction, and an inversion phenomenon occurs in which the zero-crossing point of the FM signal disappears. Therefore, the reproduction equalizer circuit (7) reduces the constriction of the reproduced FM signal by suppressing the lower sideband and emphasizing the upper sideband at the same time with the frequency characteristics shown in Fig. 11 (Fig. 10).
See C).

Next, this reproduced FM signal is passed through a limiter circuit provided at the first stage in the FM demodulation circuit (8), as shown in FIG. 10(d).
After becoming a reproduced FM signal with amplitude fluctuation components removed as shown in Figure 1, it is FM demodulated, and then the high-frequency components emphasized during recording are attenuated by the de-emphasis circuit (9), and high-frequency noise is removed. An attenuated playback video signal is obtained.

The output of the reproduction equalizer circuit (7) is also supplied to the dropout detection circuit (10), as shown in FIG. 12(a).
If a dropout occurs as shown in the playback F
The amplitude of the M signal becomes smaller and its envelope detection signal becomes the 12th signal.
The result will be as shown in figure (b). Then, the envelope detection circuit (16
) is applied to the human power X of the comparator (17), and a voltage equivalent to the normal envelope detection signal station is applied to the reference human power Y of the comparator (17), the comparator (
17), a dropout detection signal as shown in FIG. 12(C) is obtained. This dropout detection signal switches the switch circuit (12) and replaces the FM demodulated video signal output from the IH delay circuit (11) one horizontal period ago, so that dropouts are not noticeable on the screen. It is designed to compensate for

[Problems to be Solved by the Invention] Since the conventional magnetic recording/reproducing device was configured as described above, in order to further improve the S/N ratio of the video signal by suppressing noise near the upper and lower sidebands. If the characteristics of the reproduction equalizer circuit (7) are made symmetrical with respect to the carrier wave as shown in Figure 13, an imbalance between the upper and lower sidebands will remain, so the video signal as shown in Figure 10(c) will be The constriction of the reproduced FM signal in the part corresponding to the rising part is the first
As shown in Figure 4(a), it becomes even stronger and no longer crosses the slice level of the limiter circuit, so Figure 14(b)
As shown in , the limiter output of that part becomes a low frequency signal. Therefore, there is a problem in that a so-called inversion phenomenon occurs in which the video signal, which was originally at the white level, drops to the black level as shown in FIG. 14(c).

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a magnetic recording/reproducing device that does not cause the reversal phenomenon even at the rising edge of the video signal where the reproduced FM signal is constricted.

(Means and operations for solving the problem) A magnetic recording and reproducing apparatus according to the invention of claim 1 includes a first reproduction equalizer circuit that compensates a reproduction FM signal with a frequency characteristic symmetric with respect to a carrier wave, and a reproduction FM signal. a second reproduction equalizer circuit that compensates for a portion of the signal corresponding to a rising portion of the video signal with a frequency characteristic that is not constricted; a first dropout detection circuit that detects a dropout in the output of the first reproduction equalizer circuit; A second dropout detection circuit detects dropout in the output of the second reproduction equalizer circuit, and a logical operation is performed on the output of the first dropout detection circuit and the output of the second dropout detection circuit to detect the inversion phenomenon. An inversion phenomenon detection circuit that detects the period in which the inversion phenomenon occurs, and an FM demodulation circuit that replaces the output signal of the second reproduction equalizer circuit with the output signal of the first reproduction equalizer circuit only during the period when this inversion phenomenon detection signal is significant. The switch circuit according to the invention according to claim 1 is characterized in that the switch circuit according to the invention of claim 1 is characterized in that the output of the first reproduction equalizer circuit in which the S/N ratio of the demodulated FM signal is good during the period in which the inversion phenomenon does not occur. During the period in which the inversion phenomenon occurs, the output of the second reproduction equalizer circuit is applied to the FM demodulation circuit, so that a reproduction FM demodulated video signal without the inversion phenomenon and with a good S/N ratio can be obtained.

The magnetic recording/reproducing device according to the invention of claim 2 is the invention of claim 1, which includes an oscillator that generates a compensation signal of a frequency corresponding to the gray level or white level of the video signal, and only during a period when the inversion phenomenon detection signal is significant. In the invention of claim 2, the addition means includes an addition means for adding the compensation signal to the output of the first reproduction equalizer circuit and inputting the result to the FM demodulation circuit. , the output of the first reproducing equalizer circuit in which the S/N ratio of the demodulated FM signal is good is added to the output signal of the first reproducing equalizer circuit during the period in which the inversion phenomenon occurs, and the compensation signal is added to the output signal of the first reproducing equalizer circuit. , the same effect as the invention of claim 1 can be obtained.

〔Example〕

An embodiment of the invention according to claim 1 will be described below with reference to the drawings.

FIG. 1 is a block circuit diagram showing the configuration of the playback part of this embodiment, and (78) is a first playback equalizer circuit. The frequency characteristics of the reproduced FM signal received from the regenerative amplifier (6) are corrected using the characteristics shown. (7b) is the second
The reproduction equalizer circuit reproduces FM with frequency characteristics that do not constrict the part corresponding to the rising part of the video signal.
Correct the signal. (10a) is a first dropout detection circuit that detects a period in which an inversion phenomenon and a dropout occur from the amplitude of the reproduced FM signal output from the first reproduction equalizer circuit (7a). (10b) is the second dropout detection circuit, and the second reproduction equalizer circuit (7b)
) Detect the period in which dropout occurs from the amplitude of the output reproduced FM signal. (12) is a first switch circuit that performs dropout compensation; (19) is an inverter that inverts the polarity of the output of the second dropout detection circuit (10b);
(20) is an AND gate which inputs the pressure of the inverter (19) and the output of the first dropout detection circuit (LOA) and outputs an inversion phenomenon detection signal with a pulse width corresponding to the period in which the inversion phenomenon occurs; (21) FM by switching the outputs of the first and second reproduction equalizer circuits (7a) and (7b).
The second switch circuit supplies the signal to the demodulation circuit (8), and the inverter (19) and AND gate (20) constitute an inversion phenomenon detection circuit (30).

Next, the operation of this embodiment will be explained.

Note that the operations of the same parts as those in the conventional example shown in FIG. 8 are the same as those in the conventional example, so explanations thereof will be omitted.

The reproduced FM signal read from the magnetic tape (5) and amplified by the reproduction amplifier (6) is input to first and second reproduction equalizer circuits (7a) and (7b). 1st
The reproduction equalizer circuit (7a) makes the modulation index equal to that during recording by compensating with the frequency characteristics shown in FIG.
In addition, the upper and lower sidebands are suppressed to improve the S/N ratio, and the constriction of the reproduced FM signal is slightly reduced (first
(See Figure 0 (C)).

In addition, the second reproduction equalizer circuit (7b) is configured such that the spectrum of the manually inputted reproduction FM signal is, for example, as shown in FIG. 2(a).
As shown in Fig. 2(b), if the lower sideband amplitude is three times that of recording and the upper sideband amplitude is twice that of the station.
As shown in Figure 2, the frequency characteristics are such that the amplitude is doubled at the lower sideband frequency and doubled at the upper sideband frequency, and the output of the second reproduction equalizer circuit (7b) is as shown in Figure 2. As shown in FIG. 3(C), the amplitudes of the upper and lower sidebands are the same as those during recording, and compensation is made so that the portion corresponding to the rising edge of the video signal does not become constricted as shown in FIG. 3(b). Therefore, the second dropout detection circuit (1
0b) cannot detect the period during which the reversal phenomenon occurs, but only detects dropouts.

The dropout detection signal output from the second dropout detection circuit (10b) switches the first switch circuit (12) to output the video signal of one horizontal period before the IH delay circuit (11). By replacing it with , it is possible to accurately compensate for dropouts so that they are not noticeable on the screen.

Next, for example, the characteristics of the head (4) change and the imbalance between the upper and lower sidebands becomes even stronger, and the output of the first reproduction equalizer circuit (7a) becomes significantly constricted as shown in FIG. 4(C). When an inversion phenomenon occurs, the first dropout detection circuit (LOA) outputs an inversion phenomenon detection signal and a dropout detection signal (see Fig. 4(e)) of the reproduced FM signal.
) is output and manually input to the AND gate (20). On the other hand, the second dropout detection signal is connected to the inverter (
After the polarity is reversed in 19), AND game) (20)
is manually powered.

Therefore, the output of the AND gate (20) is a reversal phenomenon detection signal (see FIG. 4(g)) which detects only the period during which the reversal phenomenon occurs and does not include the dropout detection signal.

The second switch circuit (21) selects the output of the second reproduction equalizer circuit (7b) only during the period in which the inversion phenomenon occurs based on this inversion phenomenon detection signal, and the FM demodulation circuit (8) selects the output of the second reproduction equalizer circuit (7b).
, an FM demodulated video signal without an inversion phenomenon can be obtained.

Note that in the above embodiment, the second reproduction equalizer circuit (7
As shown in Fig. 2(b), the frequency characteristic of b) is suppressed while emphasizing the upper sideband while suppressing the lower sideband, but the same effect can be obtained by using the bandpass characteristic as shown in Fig. 5. .

Next, an embodiment of the invention according to claim 2 will be described with reference to the drawings.

FIG. 6 is a block circuit diagram of this embodiment, where (24) is an oscillator that generates a compensation signal with a frequency corresponding to the gray level of the video signal, and (22) is controlled by the output of an AND gate (20). The third switch circuit (23) adds the output of the first reproduction equalizer circuit (7a) and the output of the third switch circuit (22) to form an FM demodulation circuit (8).
This is an adder that inputs to

Next, the operation of this embodiment will be explained with respect to the differences from the embodiment shown in FIG.

FIG. 7 is a signal waveform diagram of each part of this embodiment, and the third switch circuit (22) receives an inversion phenomenon detection signal (see FIG. 7(C)) from the inversion phenomenon detection circuit (30). It turns on only when the signal is turned on, and a compensation signal is manually input to the adder (23). The adder (23) adds a compensation signal to the constricted portion of the output signal of the first equalizer circuit (7a), and inputs this signal to the FM demodulation circuit (8).

Therefore, a portion of the FM demodulated video signal where an inversion phenomenon has occurred becomes a gray level, and the inversion phenomenon is reduced.

In the above embodiment, the frequency of the compensation signal is set to be a frequency corresponding to the gray level of the video signal, but it may be set to a frequency corresponding to the white level.

(Effects of the Invention) The invention of claim 1 includes a first reproduction equalizer circuit that compensates the reproduction FM signal so that the S/N of the FM demodulated video signal is the best; a second equalizer circuit that compensates for the occurrence of constriction in the portion corresponding to the rising portion; an inversion phenomenon detection circuit that detects a period in which an inversion phenomenon occurs from the outputs of the first and second equalizer circuits; means for replacing the output signal of the second equalizer circuit with the output signal of the first equalizer circuit only during a period when the inversion phenomenon detection signal is significant; means for detecting a period during which the dropout detection signal is significant;
Since the apparatus is equipped with means for replacing the previous FM demodulated signal with the previous FM demodulated signal, a reproduced FM demodulated video signal with a good S/N ratio can be obtained without an inversion phenomenon or dropout.

Further, the invention of claim 2 is the invention of claim 1, which further comprises: an oscillator that generates a compensation signal of a frequency corresponding to the gray level or white level of the video signal; Since the present invention includes means for adding the above-mentioned compensation signal to the output signal of the reproduction equalizer and inputting the result to the FM demodulation circuit, the same effect as the invention of claim 1 can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing the configuration of a reproducing system of a magnetic recording/reproducing apparatus according to an embodiment of the invention of claim 1, and FIGS. 2, 3, and 4 are diagrams for explaining the operation of this embodiment. 5 is a diagram showing another frequency characteristic example of the second equalizer circuit of this embodiment, FIG. 6 is a block circuit diagram of one embodiment of the invention of claim 2, and FIG. 7 is a diagram showing its operation. A waveform diagram for explanation, FIG. 8 is a block circuit diagram showing the configuration of a recording system and a reproducing system of a conventional magnetic recording/reproducing device, FIG. 9 is a diagram showing a dropout detection circuit of this conventional example, and FIG. A signal waveform diagram to explain the operation of the limiter in the conventional reproduction equalizer circuit and FM demodulation circuit, FIG. 11 is a characteristic diagram of the conventional reproduction equalizer circuit, and FIG. 12 explains the operation of the dropout detection circuit. FIG. 13 is a diagram showing an example of the characteristics of a conventional reproduction equalizer circuit, and FIG. 14 is a signal waveform diagram for explaining the reason why an inversion phenomenon occurs. (7a)...first reproduction equalizer, (7b)...
second reproduction equalizer, (8)...FM demodulation circuit,
(9)... day emphasis circuit, (10a)...
...First dropout detection circuit, (10b)...
・Second dropout detection circuit, (11)...IH
Delay circuit, (12), (21), (22)...
・Switch circuit, (23)... Adder, (24)...
- Oscillator, (30)...inversion phenomenon detection circuit. Note that the same symbols in each figure indicate the same or equivalent parts.

Claims (2)

[Claims] (1) a first reproduction equalizer circuit that compensates the frequency characteristics of the reproduction FM signal with characteristics symmetrical to the carrier wave;
a second reproduction equalizer circuit that compensates for a portion of the reproduction FM signal corresponding to the rising portion of the video signal with a frequency characteristic that is not constricted; and a first dropout that detects a dropout of the output of the first reproduction equalizer circuit. a detection circuit; a second dropout detection circuit that detects dropout of the output of the second reproduction equalizer circuit;
an inversion phenomenon detection circuit that performs a logical operation on the output of the first dropout detection circuit and the output of the second dropout detection circuit to detect a period in which an inversion phenomenon occurs; and the inversion phenomenon detection signal is significant. A magnetic recording/reproducing apparatus comprising: means for replacing the output signal of the second reproduction equalizer circuit with the output signal of the first reproduction equalizer circuit for a period and inputting the signal to an FM demodulation circuit. (2) In claim 1, an oscillator that generates a compensation signal with a frequency corresponding to the gray level or white level of the video signal, and the compensation signal that is controlled by the detection signal of the inversion phenomenon detection circuit to output the compensation signal to the output of the first equalizer circuit. 1. A magnetic recording and reproducing apparatus, comprising: means for adding signals, and inputs the reproduced FM signal to which the compensation signal has been added to an FM demodulation circuit only during a period when the inversion phenomenon detection signal is significant.