JPH0884318A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE: To prevent inversion without causing deteriorated S/N regardless of a frequency of a reproduced modulation (FM) carrier. CONSTITUTION: While a reproduction carrier outputted from an AGC circuit 5 is received by a feedback limiter circuit 7 via a delay circuit 6, simultaneously a demodulated luminance signal Yb ' demodulated via an equalizer 15 and a demodulator 17 or the like based on the reproduced modulation carrier whose voltage is adjusted by a DC voltage adjustment device 21 is given to the feedback limiter circuit 7, a time constant of an LPF 10 is controlled based on the demodulated luminance signal Yb ' to make the resonance frequency of the feedback limiter circuit 7 in matching with the frequency of the reproduced modulation carrier, and then the reproduced modulation carrier is amplified and undesired amplification of undesired noise is avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus, and is particularly useful when applied to a reproducing system of a video tape recorder (VTR).

[0002]

2. Description of the Related Art In a VTR (mainly 8 mm VTR), a modulated carrier frequency-modulated (FM) by a luminance signal (hereinafter referred to as "modulation carrier") is magnetically recorded and reproduced from the modulated carrier. In order to prevent a so-called inversion phenomenon that may occur when the operation is performed, there is a device including a feedback type limiter circuit before the demodulator.

FIG. 4 is a block diagram showing an example of a reproducing system of a VTR equipped with such a feedback type limiter circuit, FIG. 5 is a block diagram showing a concrete example of the feedback type limiter circuit shown in FIG. 4, and FIG. 4 is an explanatory diagram showing the frequency characteristics of the feedback type limiter circuit, and FIG. 7 is an explanatory diagram for explaining the inversion prevention operation of the feedback type limiter circuit shown in FIG. 4 and 5, 1 is a video tape on which a video signal including the modulated carrier is magnetically recorded, 2 is a magnetic head, 3 is a reproduction amplifier, 4 is a TRAP circuit, 5 is an AGC circuit, and 8 is an adder. , 9 is a limiter, 10 'is a low-pass filter (LP
F), 11 is a high-pass filter (HPF), 12 is a limiter, 13 is a demodulator, and 14 is a low-pass filter (LP).
F) and 15 are feedback circuits.

As shown in FIG. 4, the reproduction signal reproduced from the video tape 1 by the magnetic head 2 is amplified by the reproduction amplifier 3 and then output to the TRAP circuit 4. TR
The AP circuit 4 is a filter that cuts other signals such as color signals from the reproduction signal input from the reproduction amplifier 3 and extracts a luminance signal (modulation carrier FM-modulated by the luminance signal). Modulation carrier is AGC circuit 5
Output to.

The AGC circuit 5 is a circuit which automatically adjusts the level of the reproduction modulation carrier input from the TRAP circuit 4 to a predetermined value when the level of the reproduced modulation carrier does not meet the predetermined value. The subsequent reproduction modulation carrier is output to the feedback type limiter circuit 7 '.

The feedback type limiter circuit 7'includes an adder 8 and
The feedback circuit includes a high-gain limiter 9 connected to the adder 8 and a feedback circuit 15 for positively feeding back the output of the limiter 9 to the input side (adder 8) of the limiter 9. It operates as a non-linear amplifier that resonates at the resonance frequency determined by the feedback coefficient of 15. A concrete example of such a feedback type limiter circuit 7'is shown in FIG. That is, the LPF 1 is connected to the output side of the limiter 9.
0'is connected, and the output of this LPF 10 'is limited by the limiter 9
A feedback circuit is formed by the HPF 11 that feeds back to the input side (adder 8) of the LPF, and the time constant of the LPF 10 'and H
The resonance frequency is determined by the time constant of the PF 11.

This resonance frequency is, as shown in FIG. 6, a frequency above the white peak, that is, the tip of the rising portion (A portion in FIG. 6) to the white peak where sharp overshoot occurs due to pre-emphasis ( The frequency is set to correspond to the (right end in the figure), and when a reproduction modulation carrier having a frequency near the resonance frequency is input to the feedback type limiter circuit 7 ', it resonates and returns to the feedback type limiter circuit 7'.
Gain increases. The reproduced modulated carrier thus amplified is output to the limiter 12. As shown in FIG. 6, the increase in the gain of the feedback type limiter circuit 7'becomes larger as the level of the reproduced modulation carrier is lower due to its characteristic.

The limiter 12 is a feedback type limiter circuit 7 '.
After removing the level fluctuation of the reproduction modulation carrier input from the above, it is output to the demodulator 13. The demodulator 13 demodulates the modulated carrier input from the limiter 13 to restore the original luminance signal, and outputs this to the LPF 14. LP
F14 mainly removes the carrier component from the luminance signal demodulated by the demodulator 13 and then outputs it to a de-emphasis circuit (not shown).

Therefore, according to the reproducing system of the VTR having the above structure, when the amplitude of the reproduced modulation carrier output from the AGC circuit 5 becomes small at the rising to the white peak as shown in FIG. , The gain of the feedback type limiter circuit 7'increases, and as a result, the amplitude of the reproduction modulation carrier is greatly amplified as shown in FIG. 7B (see section B). Therefore, when the reproduced modulated carrier is demodulated by the demodulator 13, as shown by the solid line in FIG. 7C, the rising portion of the luminance signal to the white peak is surely reproduced without causing the inversion phenomenon. On the other hand, when the feedback type limiter circuit 7'is not provided, the signal shown in FIG. 7A is directly input to the demodulator 13 via the limiter 12, so that the zero crossing is performed in the B section. The dots are missing, and the inversion phenomenon as shown by the alternate long and short dash line in FIG. 7C occurs.

[0010]

However, in the feedback type limiter circuit 7'of the VTR according to the above-mentioned prior art, when the frequency of the reproduction modulation carrier input to the feedback type limiter circuit 7'is low, that is, the level of the luminance signal. Is close to the black level, noise having a frequency near the resonance frequency set above the white peak is unnecessarily amplified.
/ N will be deteriorated.

Therefore, in view of the above-mentioned prior art, the present invention provides a magnetic recording / reproducing device provided with a circuit capable of preventing the reversal phenomenon regardless of the frequency of the reproduction modulation carrier without causing deterioration of S / N. The purpose is to provide a device.

[0012]

The first structure of the present invention for achieving the above object is to reproduce the modulated carrier from a magnetic recording medium on which a modulated carrier frequency-modulated by a recording signal is magnetically recorded. Section, an auxiliary demodulation section for demodulating the reproduced modulated carrier reproduced by the reproducing section without causing an inversion phenomenon, a limiter, and positive feedback of the output of the limiter to the input side of the limiter and the auxiliary demodulating section. And a feedback circuit whose feedback coefficient changes according to the demodulated recording signal demodulated in 1., and the resonance frequency determined by the feedback coefficient matches the frequency of the reproduction modulation carrier, and the gain is obtained only for signals near this frequency. Feedback limiter circuit that operates as a non-linear amplifier with increasing noise, and the playback modulation carrier amplified by this feedback limiter circuit. Characterized by comprising a main demodulation unit for demodulating a.

A second configuration of the present invention that achieves the above object is the same as the first configuration, in which the feedback circuit of the feedback type limiter circuit is connected to the output side of the limiter, and a low-pass filter of this low-pass filter. And a high-pass filter for returning the output to the input side of the limiter, wherein the time constant of the low-pass filter or the high-pass filter changes according to the demodulation recording signal demodulated by the auxiliary demodulation unit. And

A third structure of the present invention which achieves the above object is the above-mentioned first or second structure, wherein the lower demodulation wave level is lowered in the preceding stage in the auxiliary demodulation section to lower and upper side band waves. It is characterized by being provided with an equalizer for balancing.

A fourth structure of the present invention which achieves the above object is the reproduction modulation carrier according to the first, second or third structure, wherein the voltage value of the demodulated recording signal demodulated by the auxiliary demodulation unit is reproduced. In order to adjust to the optimum voltage value for matching the resonance frequency of the feedback type limiter circuit with the frequency of, a DC voltage adjuster capable of arbitrarily adjusting the value of the DC voltage added to the demodulation recording signal is provided. Characterize.

A fifth structure of the present invention which achieves the above object is the above-mentioned first, second, third or fourth structure.
It is characterized in that the input side of the feedback type limiter circuit is provided with a delay circuit for correcting the time shift between the reproduction modulation carrier and the demodulated recording signal input to the feedback type limiter circuit.

According to a sixth aspect of the present invention which achieves the above object, in the first, second, third, fourth or fifth configuration, the recording signal is a luminance signal and the magnetic recording medium is It is a video tape.

[0018]

According to the present invention having the above-mentioned first to sixth structures, the demodulation recording signal (demodulation luminance signal, etc.) output from the auxiliary demodulation section.
The feedback coefficient (time constant of the low-pass filter or high-pass filter) changes due to the change of the resonance frequency of the feedback type limiter circuit, and this resonance frequency and the frequency of the reproduction modulation carrier input to the feedback type limiter circuit are changed. Match. For this reason, the gain of the feedback type limiter circuit is increased to amplify the reproduction modulation carrier, while the noise of the frequency apart from the frequency of the reproduction modulation carrier is not unnecessarily increased.

Further, by providing the equalizer as in the third configuration, it is possible to easily prevent the inversion phenomenon at the time of demodulation in the auxiliary demodulation section, and by providing the DC voltage adjuster as in the fourth configuration, demodulation recording By adjusting the voltage value of the signal arbitrarily, the resonance frequency of the feedback type limiter circuit and the frequency of the reproduction modulation carrier are surely made to coincide with each other, and further, by providing the delay circuit as in the fifth configuration, the feedback type limiter circuit is provided. It is possible to surely match the timings of the input reproduction modulation carrier and the demodulation recording signal.

[0020]

Embodiments of the present invention will now be described in detail with reference to the drawings. The same parts as those of the conventional technology (FIGS. 4 and 5) are designated by the same reference numerals, and the detailed description thereof will be omitted.

FIG. 1 is a block diagram showing a reproducing system of a VTR according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing details of a low-pass filter provided in the feedback type limiter circuit shown in FIG. 1, and FIG. It is explanatory drawing which shows the frequency characteristic of the feedback type limiter circuit shown in FIG. 1 and 2, 6 is a delay circuit, 7 is a feedback type limiter circuit, 10 is a low pass filter (LPF), 10a is a resistor, 10b is a capacitor, 1
0c is a varicap, 15 is an equalizer, 16 is a limiter, 17 is a demodulator, and 18 is a low-pass filter (LP).
F), 19 are amplifiers, 20 is an adder, 21 is a DC voltage regulator, and others are the same as those shown in FIGS. 4 and 5.

That is, the VTR reproducing system according to the present embodiment is the LPF1 in the conventional VTR reproducing system (FIGS. 4 and 5).
The LPF 10 is provided instead of 0 ', and the delay circuit 6, the equalizer 15, the limiter 16, the demodulator 17, and the LPF 1 are provided.
8, an amplifier 19, an adder 20, and a DC voltage regulator 21 are additionally provided.

Among them, the LPF 10 is an RC filter composed of a resistor 10a and a capacitor 10b as shown in FIG.
0c is provided. Varicap 10c is adder 2
It is connected to the positive side of the DC voltage regulator 21 via 0, and the negative side of the DC voltage regulator 21 is grounded. Further, the demodulation luminance signal Y _b (described later in detail) output from the amplifier 19 is input to the adder 20, and the output voltage of the DC voltage regulator 21 is added to the demodulation luminance signal Y _b .

[0024] Therefore burr cap 10c 'are applied, the demodulated luminance signal Y _b' demodulated luminance signal Y _b obtained by adding the output voltage of the DC voltage regulator in the demodulated luminance signal Y _b capacitance of the varicap 10c by Changes. As a result, the time constant of the LPF 10 changes, and the feedback type limiter circuit 7
The resonance frequency of changes.

On the other hand, the equalizer 15 inputs the reproduction modulation carrier output from the AGC circuit 5, balances the upper sideband and the lower sideband of the reproduction modulation carrier, and then outputs this to the limiter 16. . That is, the AGC circuit 5
When the modulation index (ratio of frequency shift and luminance signal frequency) is small, such as the rising part to the white peak, the reproduced modulated carrier output from the low sideband is emphasized and the upper sideband is suppressed. Since it is in a balanced state, the level of the lower sideband is lowered to balance it with the upper sideband, thereby preventing the inversion phenomenon when the reproduced modulated carrier is demodulated in the demodulator 17 described later. .

Limiter 16, demodulator 17 and LPF 18
Is similar to the limiter 12, demodulator 13 and LPF 14 described above, and demodulates the reproduced modulated carrier output from the equalizer 15 to obtain a demodulated luminance signal.
The demodulated luminance signal is output to the amplifier 19. Amplifier 19
Amplifies the demodulated luminance signal input from the LPF 18 and outputs it to the adder 20 (demodulated luminance signal Y _b ) as described above.

The delay circuit 6 is provided in front of the adder 8,
The time lag between the reproduced modulated carrier and demodulating the luminance signal Y _b ', which is input to the feedback limiter circuit 7 corrects timing the two. Specifically, the delay time of the LPF 18 is set as the delay time of the delay circuit 6.

Therefore, according to the present embodiment, when the reproduction modulation carrier output from the AGC circuit 5 is input to the feedback type limiter circuit 7 via the delay circuit 6, at the same time, the equalizer is based on the reproduction modulation carrier at this time. The demodulated luminance signal Y _b ′, which is demodulated through 15, the limiter 16, the demodulator 17, the LPF 18 and the amplifier 19 and whose voltage value is adjusted by the DC voltage adjuster 21, is also input to the feedback limiter circuit 7. As a result, the time constant of the LPF 10 is controlled on the basis of the reproduction luminance signal Y _b ′ at this time, and the resonance frequency of the feedback limiter circuit 7 determined by this time constant,
The frequency of the reproduction-modulated carrier matches, and only the signal in the vicinity of this frequency is greatly amplified by the increase in gain.

That is, as shown in FIG. 3, when the frequency of the re-modulated carrier is a frequency corresponding to the level of the white peak or higher, the gain is increased only for a signal near this frequency as in the conventional case (in the figure, Y ₃ reference) to one, for example in the case of a frequency frequency of the reproduced modulated carrier is equivalent to the gray level in this frequency becomes the resonance point of the feedback type limiter circuit 7 gain increases only for the signal of the frequency neighborhood (FIG. Y ₂ reference) and in, also the gain only for signals of the frequency near the frequency becomes the resonance point of the feedback type limiter circuit 7 in the case of a frequency frequency of the reproduced modulated carrier is equivalent to the black level To increase. Thus, unnecessary noise other than the reproduction modulation carrier is not increased unnecessarily, and no matter what frequency the reproduction modulation carrier is, the inversion phenomenon is prevented and the luminance signal Y _a is not deteriorated without deteriorating the S / N. Therefore, good image quality can be obtained.

Further, by providing the equalizer 15, the inversion phenomenon at the time of demodulation in the demodulator 17 can be easily prevented, and the voltage value of the demodulation luminance signal Y _b ′ by providing the DC voltage regulator 2 can be arbitrarily set. The resonance frequency of the feedback type limiter circuit 7 and the frequency of the reproduction modulation carrier can be surely adjusted by adjusting so that the reproduction modulation carrier and demodulation input to the feedback type limiter circuit 7 are demodulated by providing the delay circuit 6. it can be allowed to coincide reliably the timing of the luminance signal Y _b '.

In order to control the resonance frequency of the feedback type limiter circuit 7 at low cost by controlling the time constant, the time constant of the LPF 10 is set to the demodulation luminance signal Y _b ′ as in the above embodiment rather than the time constant of the HPF 11. Although the control is more suitable, the time constant of the HPF 11 may be controlled without being limited to this.

In the above embodiment, as shown in FIG.
Feedback type limiter circuit 7 including PF10 and HPF11
However, the feedback limiter circuit 7 is not limited to the feedback limiter circuit 7. In short, the feedback coefficient of the feedback circuit in the feedback limiter circuit is demodulated luminance signal Y.
controlled by _b ', as long as the resonance frequency of the feedback limiter circuit can be matched to the frequency of the reproduction modulated carrier.

[0033]

According to the present invention as specifically described above with reference to the embodiments, since the resonance frequency of the feedback type limiter circuit and the frequency of the reproduction modulation carrier input to the feedback type limiter circuit match. It is possible to prevent the inversion phenomenon without deteriorating the S / N regardless of the frequency of the reproduction modulation carrier. Further, by providing the equalizer, it is possible to easily prevent the inversion phenomenon at the time of demodulation in the auxiliary demodulation unit, and by providing the DC voltage adjuster, the voltage value of the demodulated recording signal can be arbitrarily adjusted and the feedback limiter circuit The resonance frequency and the frequency of the reproduction modulation carrier can be matched with certainty, and the timing of the reproduction modulation carrier and the demodulation recording signal input to the feedback type limiter circuit can be surely matched by providing the delay circuit. You can

[Brief description of drawings]

FIG. 1 is a block diagram showing a reproduction system of a VTR according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing details of a low-pass filter provided in the feedback type limiter circuit shown in FIG.

FIG. 3 is an explanatory diagram showing frequency characteristics of the feedback type limiter circuit shown in FIG.

FIG. 4 is a block diagram showing a reproduction system of a VTR according to a conventional technique.

5 is a block diagram showing a concrete example of the feedback type limiter circuit shown in FIG.

FIG. 6 is an explanatory diagram showing frequency characteristics of the feedback type limiter circuit shown in FIG.

FIG. 7 is an explanatory diagram explaining an operation of the feedback type limiter circuit shown in FIG.

[Explanation of symbols]

1 Video Tape 2 Magnetic Head 3 Playback Amplifier 4 TRAP Circuit 5 AGC Circuit 6 Delay Circuit 7 Feedback Type Limiter Circuit 8, 20 Adder 9, 12, 16 Limiter 10, 14, 18 Low Pass Filter 10a Resistor 10b Capacitor 10c Varicap 11 High Pass filter 13 and 17 demodulator 15 equalizer 19 amplifier 21 DC voltage regulator _{Y a, Y b, Y b} ' demodulated luminance signal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04N 5/93

Claims (6)

[Claims] 1. A reproducing unit for reproducing the modulated carrier from a magnetic recording medium on which a modulated carrier frequency-modulated by a recording signal is magnetically recorded, and an inversion phenomenon occurs in the reproduced modulated carrier reproduced by the reproducing unit. Auxiliary demodulator without performing the demodulation, a limiter for inputting the reproduction modulation carrier, an output of the limiter is positively fed back to the input side of the limiter, and according to a demodulation record signal demodulated by the auxiliary demodulator. A feedback type limiter operating as a non-linear amplifier having a feedback circuit in which the feedback coefficient changes, and the resonance frequency determined by the feedback coefficient matches the frequency of the reproduction modulation carrier and the gain increases only for signals in the vicinity of this frequency. Circuit and a main demodulation unit for demodulating the reproduction modulation carrier amplified by this feedback type limiter circuit. A magnetic recording / reproducing apparatus characterized by the above. 2. The magnetic recording / reproducing apparatus according to claim 1, wherein the feedback circuit of the feedback-type limiter circuit is a low-pass filter connected to the output side of the limiter, and the output of the low-pass filter is connected to the input side of the limiter. A magnetic recording / reproducing apparatus, comprising: a high-pass filter for feedback, wherein a time constant of the low-pass filter or the high-pass filter changes according to a demodulated recording signal demodulated by the auxiliary demodulation unit. 3. The magnetic recording / reproducing apparatus according to claim 1 or 2, wherein an equalizer is provided in a front stage of the auxiliary demodulation section for lowering the level of the lower band wave to balance the upper and lower band waves. A magnetic recording / reproducing apparatus characterized in that 4. The magnetic recording / reproducing apparatus according to claim 1, 2 or 3, wherein the voltage value of the demodulated recording signal demodulated by the auxiliary demodulation unit is set to the frequency of the reproduction modulation carrier and the resonance frequency of the feedback type limiter circuit. The magnetic recording / reproducing apparatus is provided with a DC voltage adjuster capable of arbitrarily adjusting the value of the DC voltage added to the demodulated recording signal in order to adjust the voltage value to the optimum value. 5. The magnetic recording / reproducing apparatus according to claim 1, 2, 3 or 4, wherein a reproduction modulation carrier and a demodulation recording signal which are input to the feedback type limiter circuit are input to the input side of the feedback type limiter circuit. A magnetic recording / reproducing apparatus having a delay circuit for correcting a time lag. 6. The magnetic recording / reproducing apparatus according to claim 1, 2, 3, 4 or 5, wherein the recording signal is a luminance signal and the magnetic recording medium is a video tape. apparatus.