JPS62289077A - Magnetic recoding and reproducing device - Google Patents

Abstract

PURPOSE:To maintain a well-balanced output from an FM equalizer by inserting a reference signal into a video signal so as to record it, detecting it at the time of reproduction and adjusting the frequency characteristic of an FM equalizer circuit. CONSTITUTION:At the time of recording, a gate circuit 10 gates the output of a reference signal generator circuit 9 with the aid of the output of a logic circuit 4, and an adder 13 inserts the reference signal into a video signal input 1. Upper and lower band level detection signals arise in the output spectrum of an FM modulator circuit 2. At the time of reproduction, a band-pass filter BPF 21 passes only an upper side band frequency, while a BPF 22 passes through only a lower side band frequency. A reproduction video signal is supplied to a logic circuit 4 from a demodulator circuit 20. A sample holding circuit 26 sample-holds the output of a level difference detection circuit 25 at a timing when the reference signal is inserted at the time of recording. The FM equalizer circuit 18 varies its frequency characteristic in accordance with a feedback level, and the output of a head amplifier 16 is well balanced.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Field of Industrial Application The present invention relates to a magnetic recording and reproducing apparatus that records and reproduces video signals using a recording medium such as a magnetic tape.

Conventional technology In recent years, there has been a demand for higher image quality in VTRs, and H
Technologies such as the Q system or the Iband system have been introduced, but the most important factor in achieving high image quality is improving the FM transmission characteristics of the tape head system.

The tape head system of a VTR can be viewed as a type of FM transmission path, and when recording and reproducing low-carrier FM signals, a ``sideband imbalance phenomenon'' occurs in which the lower sideband is generally emphasized and the upper sideband is suppressed. , when the level difference between the upper side band wave and the lower side band wave becomes large, an inversion phenomenon, so-called blurring phenomenon occurs. At this time, the FM regeneration force waste vector is as shown in FIG. 7, for example. In FIG. 7 f. is the carrier frequency in FM modulation, and f is the modulation frequency.

In VTRs, in order to solve the above-mentioned problems, an FM equalizer circuit is installed in the head amplifier circuit, which results in lowering the level of the lower sideband and achieving balance with the upper sideband. FIG. 8 shows a block diagram of a conventional FM signal transmission system. In FIG. 8, 101 is a video signal input, 102 is an FM modulation circuit, 103 is a recording amplifier circuit, 1
04 is the video head, 1o6 is the video tape, 106 is the head amplifier circuit, 107 is the first stage amplifier circuit, ios is F
M equalizer circuit, 109 limiter/demodulation circuit, 11
0 is the video signal output, and 111°, 112, and 113 are 7 during recording, playback, and sideband balance correction, respectively.
M spectrum.

As mentioned above, the unbalance 112 of the upper and lower sidebands generated in the tape head systems 104 and 105 is corrected by the head amplifier circuit 10.
The FM equalizer circuit 108 in 6 corrects the signal as shown in 113 so that it has the same characteristics as the FM spectrum 111 during recording.

(The characteristics of the first stage amplifier circuit 107 are flat.) FIG. 9 shows a detailed diagram of the FM equalizer circuit 108 in the conventional example, where 112 is the FM equalizer input, 113 is the 7M equalizer output, 114 is a transistor, 115 is an inductance, 116 is a capacitor, 11
7 is resistance. Figure 9 shows an emitter peaking circuit, and the FM equalizer output 113 has an inductance of 115t.
It has a characteristic that has a peak at the resonant frequency f determined by Ll and the capacitor 16 (C1."zrcJT2), and its level is adjusted by the resistor 117.
For MIJ VTRs, it is set around 6 to 7141z.

Problems to be Solved by the Invention However, in the above configuration, the frequency characteristics of the FM equalizer circuit are fixed, so the F of the tape head system
If the M transmission characteristics change for some reason, there is a problem in that the balance between the upper and lower side waves of the 7M spectrum of the 7M equalizer output is lost, causing an inversion phenomenon. Possible changes in the FM transmission characteristics of the tape head system include deterioration of the characteristics of the tape head itself due to long-term use and differences in the type and material of the tape used.

In view of the above-mentioned problems, the present invention has been developed so that the upper and lower sideband levels of the 7M spectrum obtained in the output of the 7M equalizer are set to the upper and lower sideband levels when the reference signal inserted at a predetermined position of the V blanking of the video signal during recording is reproduced. Magnetic recording and playback system that uses comparative detection to utilize the phenomenon occurring in the 7M equalizer to maintain a stable 7M equalizer output with a well-balanced upper and lower sideband even if the FM transmission characteristics of the tape head system change. It provides equipment.

Means for Solving the Problems In order to solve the above problems, the magnetic recording and reproducing apparatus of the present invention uses a reference signal for detecting the upper sideband and lower sideband levels in a predetermined vertical blanking section of the video signal. means for inserting into the horizontal period of the recording medium to record on the recording medium, and a first . The device includes a second filter, a detection circuit that detects a level difference between output signals of the first and second filters, and an FM equalizer circuit that can vary frequency characteristics using the output of the detection circuit. .

Effect of the present invention With the above-described configuration, the present invention detects the level difference between the signals generated in the upper and lower sidebands in the FM spectrum obtained from the output of the FM equalizer circuit, and uses a control signal corresponding to this level difference to By adjusting the frequency characteristics of the FM equalizer circuit, changes in FM transmission characteristics due to the tape head system can be absorbed, and as a result, the 7M equalizer output can be maintained in a well-balanced manner.

EXAMPLES Below, a magnetic recording/reproducing apparatus of the present invention will be explained with reference to the drawings. FIG. 1 shows a block diagram of a first embodiment of the present invention. In FIG. 1, 1 is a video signal input, 2 is an FM modulation circuit, 3 is a recording amplifier circuit, 4 is a logic circuit, 6 is a horizontal synchronization signal separation circuit, 6 is a vertical synchronization signal separation circuit, 7 is a counter circuit, and 8 1 is a mono multi circuit, 9 is a reference signal generation circuit, 10 is a gate circuit, 11° 12 is a switch, 13 is an adder, 14 is a magnetic hesode, 1
6 is a magnetic tape, 16 is a head amplifier circuit, 17 is a first stage amplifier circuit, 18 is an FM equalizer circuit, 19 is a limiter circuit, 2o is a demodulation circuit, 21 is a band pass filter for detecting one sideband, 23U lower sideband A band pass filter for detection, 22 and 24 a level detection circuit, 26 a level difference detection circuit, 26 a sample hold circuit, 27 a low pass filter, and 28 a video signal output.

The operation of the magnetic recording/reproducing apparatus configured as described above will be described below.

During recording, the video signal 1 is FM'd by the FM modulation circuit 2, amplified by the recording amplification circuit 3, and then recorded from the magnetic head 14 onto the magnetic tape 16.
Signals for detecting the upper and lower sideband levels of the M spectrum are inserted by circuits 4 to 13 into predetermined horizontal periods of the V blanking section of the video signal before FM modulation. FIG. 2 is a diagram for explaining the operation of circuits 4 to 13, and a to n are input and output waveforms of each circuit. Video signal human power 1
is input to the horizontal synchronizing signal separation circuit 6 through the switch 11 connected to the R side during recording (FIG. 2a), and the composite synchronizing signal pulses are separated. (FIG. 2b) 6 is a vertical synchronization signal separation circuit which extracts a vertical synchronization pulse from the composite synchronization signal. (Fig. 2 g) The counter circuit is configured to count the number of composite synchronous pulses (Fig. 2 b) after being reset by the vertical synchronizing pulse (Fig. 2 g).
Make sure that a pulse is generated at a predetermined position of the horizontal synchronization pulse as shown in . Reference numeral 8 is a mono multi-circuit that generates a gate pulse between horizontal synchronizing pulses from the output of the counter circuit 7 (Fig. 2 d) as shown in Fig. 2 e. Although the color burst is omitted in the diagram, it is actually It is necessary to set e at a position that does not affect the color burst.

The gate pulse is applied to the switch 12 connected to H during recording.
is supplied to the gate circuit 10 with a diameter of .

9 is a reference signal generating circuit for generating signals for detecting the upper and lower side band levels of the reproduced FM spectrum, and generates a single wave as shown in FIG. 2(f). (The appropriate frequency is 1 to 2 MHz.) The gate circuit 10 gates the output of the detection signal generation circuit 9 (FIG. 2 f) with the output of the monomulti circuit 7 (FIG. 2 e). Function: Outputs the signal shown in Figure 2g. The adder 13 receives the video signal manually (Fig. 2a) and the output of the gate circuit 1o (Fig. 2g)
is minxed and a signal in which a reference signal is inserted in a predetermined horizontal period of the V blanking section of the video signal as shown in the second figure is supplied to the FM modulation circuit 2.

FIG. 3 is an example of the output vector of the FM modulation circuit 2 when the video signal input is a video sweep signal and the frequency of the reference signal is f.
Signals for detecting the levels of the upper and lower sidebands can be generated at the point fP. In the case of constant current recording, since the spectrum of the recording current is the same as the spectrum of the FM modulation output, a signal having the spectrum shown in FIG. 3 is recorded on the magnetic tape 15.

During reproduction, the reproduction signal extracted by the magnetic head 14 is supplied to the head amplifier circuit 16. Head amplifier circuit 16
consists of a first-stage amplifier circuit 17 and an FM equalizer circuit 18. After correcting the distortion of FM transmission characteristics in the tape head system, it is limited by an IJ emitter circuit 19, demodulated by a demodulator circuit 2o, and reproduced to an output 28. Outputs a video signal. Circuits 21 to 27.4 and 11.12 are circuits for keeping the output power vector of the FM equalizer circuit 18 stable, and their operation will be explained below. The output of the FM equalizer circuit 18 is supplied to the limiter circuit 19 and also to the BPF 21.23. The BPF is the third
The BPF 21 passes the signal generated at f±f shown in the figure, and the BPF 21 passes the upper side band wave (f + f), and the BPF 22 passes the lower side band wave CP (f − f). 22.24
CP is a level detection circuit that generates a level according to the signals obtained by BPF21 and BPF23, and the output of the level difference detection circuit 25 has an upper sideband wave (fo+fP) and a lower sideband wave (f0+fP).
A C P voltage corresponding to the level difference of -f) is generated. 26 is a sample hold circuit, and the sample timing is the same as that in FIG. 2e in which a detection signal is inserted during recording. This sample pulse can be obtained by sharing the logic circuit 4 used during recording. During reproduction, the switch 11 is connected to the P side, and the logic circuit 4 is supplied with the reproduced video signal obtained by the demodulation circuit 2o.

The logic circuit 4 undergoes the same process as in the case of recording described above, and the pulse shown in FIG. 2e is obtained at its output in the same manner as in the case of recording. Since the switch 12 is connected to the P side during reproduction, the sample and hold circuit 26 samples and holds the output of the level difference detection circuit 25 at the timing when the reference signal is inserted during recording (FIG. 2e). The output of the sample and hold circuit 26 passes through a low-pass filter 27 for slowing down the response, and then passes through the FM in the head amplifier circuit 16.
The signal is fed back to the equalizer circuit 18, and the FM equalizer circuit is configured to change its frequency characteristics according to the feedback level. This situation will be explained using FIG. 4. In Figure 4, (input is a state where the upper and lower sidebands are balanced,
(B) shows a state where the upper and lower sidebands are unbalanced, (1) is the output loss vector of the head amplifier circuit 16, (2) is the output voltage of the halo pass filter 27, and (3) is the FM equalizer circuit. 18 frequency characteristics are shown. Also f. is the carrier frequency and f is the detected signal frequency.

The upper and lower sidebands are balanced (in the N state, the output loss vector of the head amplifier circuit 16 is (At - (1
1, and since +fP and -f are at the same level, the output of the low-pass filter 27 is 0, like (Al-(2+), and the frequency characteristic of the FM equalizer circuit 18 is (
Al - (31 is the basic frequency characteristic. Now, if for some reason the balance between the upper and lower sidebands is lost, the output loss vector of the head amplifier circuit 16 is, for example (Bl - (11, and if this continues, there is a possibility that an inversion phenomenon will occur due to the balance insertion of the upper and lower sideband waves. However, at this time, the low-pass filter 27
Since the output of is a3+-(2+, this voltage is used to change the frequency characteristics of the FM equalizer circuit 18 to (Al
-(31 to (B)-(If you change it so that the upper and lower sidebands are balanced as shown in 31, the head amplifier circuit 1
The output vector of 6 is maintained in a balanced state as shown in (A)-(11).

13...- FIG. 5 is a block diagram of the FM equalizer circuit in the first embodiment of the present invention. Figure 6 shows a method of varying the gain of the FM equalizer circuit by changing the amount of damping; 29 beams are a peaking circuit created using C resonance, etc., and 3o is a damping circuit that adjusts the gain of the FM equalizer circuit. , 31 is a control signal input, 32 is F
This is the M equalizer circuit output. FM equalizer circuit 18
The output of the first stage amplifier circuit 17 of FIG. 1 is supplied to the input of , and the output of the low-pass filter 27 of FIG. 1 is supplied to the input of . In the FM equalizer circuit 18, the amount of damping of the damping circuit 3o changes according to the voltage input to 31, so that as a result, the frequency characteristics (gain) of the FM equalizer circuit 18 can be changed by the voltage 31, and the FM equalizer circuit 18 The spectrum of the output 32 of is always kept stable.

FIG. 6 is a configuration diagram of a second embodiment of the FM equalizer circuit according to the present invention. Figure 6 shows FM equalizer circuit 1
8 is used to vary the peak frequency, 33 is a transistor, 34 is an inductance, 36 is a capacitor,
36 is a resistor, 37 is a variable capacitance diode, 38 is a control signal input, and 39 is an FM equalizer circuit output. 38 is supplied with a control signal that detects the balance difference between the upper and lower sidebands as described above, and the variable capacitance diode 3 can change its capacitance depending on the control signal voltage.As a result, the FM equalizer circuit is controlled by the voltage of 38. 18 frequency characteristics (peak frequency) can be changed, and the FM equalizer circuit output 39 can be kept in a stable state.

In the above embodiment, on the reproduced FM spectrum,
The signal for detecting the lower sideband level was obtained by inserting a reference signal into a predetermined horizontal period of the V blanking section of the video signal during recording and FM modulating this signal, but other means are available. After FM modulating the video signal as (f.

It is also conceivable to provide two signal sources, 10f, ) and (fc-fP), and create this signal by superimposing it on the FM luminance signal.

Furthermore, when a compatible tape is played back, no detection signal is detected, so the frequency characteristics of the FM equalizer circuit operate in a fixed state.

Effects of the Invention As described above, according to the present invention, in order to obtain signals for detecting the upper sideband and lower sideband levels of the FM spectrum during reproduction, the reference signal is set at a predetermined interval in the V blanking section of the video signal. FM in the head amplifier circuit is inserted into the horizontal period and recorded, and during playback, the level difference between the signals generated in the upper side band and lower side band of the cass vector for the head amplifier circuit is detected.
By controlling the frequency characteristics of the equalizer circuit using the level difference signal, it is possible to maintain the FM spectrum at the head amplifier output in a balanced state at all times. It is possible to correct the unbalance of the FM spectrum and obtain a stable reproduction output that is resistant to inversion phenomena.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the first embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the main circuit operation during recording in FIG. 1, and FIG. 3 is an FM modulation spectrum diagram in the present invention. , FIG. 4 is an explanatory diagram of the main circuit operation during reproduction of FIG. 1, FIG. 6 is a block diagram of the FM equalizer circuit in the first embodiment of the present invention, and FIG. 6 is the FM equalizer circuit in the present invention. 7 is an FM spectrum diagram when an inversion phenomenon occurs, FIG. 8 is a block diagram of a conventional FM signal transmission system, and FIG. 9 is a detailed diagram of a conventional FM equalizer circuit. It is. 4...Logic circuit, 9...Reference signal generation circuit, 1o...Gate circuit, 16...
...Head amplifier circuit, 21...BPFl, 23
・River...LPF2.22...Level detection circuit,
26... Level difference detection circuit, 26... Sample hold circuit, 27... LPF.

Claims (1)

[Claims] Means for inserting a reference signal for detecting an upper side band level and a lower side band level in an occupied band of a reproduced video signal into a predetermined horizontal period of a vertical blanking section of the video signal, frequency modulating the signal, and recording the frequency modulated signal on a recording medium. and first and second channels that respectively pass signals generated in the upper sideband and lower sideband in the occupied band of the video signal generated by frequency modulation recording and reproduction of the reference signal from the reproduced video signal. a filter means, a detection circuit for detecting a level difference between the output signals of the first and second filters, and an output of the detection circuit to maintain the frequency characteristic in the occupied band of the reproduced video signal to a desired characteristic. A magnetic recording/reproducing device comprising an FM equalizer circuit that can vary its frequency characteristics.