JPH0691664B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording / reproducing apparatus (hereinafter abbreviated as VTR) capable of making adjustment of a recording current of a video signal in a helical scan type video tape recorder. is there.

(Background of the Invention) FIG. 8 shows a video signal recording circuit for home use, for example, a VHS system VTR. In the figure, the video signal a is separated into a luminance signal b and a color signal c by a low pass filter (hereinafter abbreviated as LPF1) and a band pass filter (hereinafter abbreviated as BPF2).

The luminance signal b is FM-modulated by the FM modulation circuit 3 and then input to the mixing circuit 5 via the level adjuster 4. Further, the color signal c is low-pass converted by the low-pass conversion circuit 6 and then input to the mixing circuit 5 via the level adjuster 7.

These signals are mixed by the mixing circuit 5, and then input to the gain switching circuit 14 whose gain is switched by the mode switching signal 15 described later. Further, the output of the gain switching circuit 14 is supplied to the rotary transformer 11 via the recording / amplifying circuit 8 and recorded on the magnetic tape by the magnetic heads 9 and 10 alternately tracing the magnetic tape. The output of the recording amplifier circuit 8 is supplied to the resistor 13 and output from the output terminal 12. The output terminal 12 is used as a terminal for taking out a monitor signal during the level adjustment of the level adjusters 4 and 7.

By the way, in recent years, magnetic recording / reproducing characteristics of video signals have been improved with the improvement of magnetic heads and magnetic tapes. For this reason, the tape running speed is slowed down, for example, VHS system V
In TR, the original standard mode (tape running speed 33.35mm / se
In comparison with c), the 1/3 speed triple mode has been established and popularized.
As is well known, according to the triple mode, it has been confirmed that the required tape amount is small and a desired S / N can be obtained.

In a VTR that can be used by switching between the standard mode and the triple mode, the video track width of the recording pattern differs in each mode. However, if a magnetic head pair having a track width corresponding to the video track width of each mode is provided for each mode, the best reproduced image quality can be obtained in both modes. The above gain switching circuit
In 14, the gains are switched so that the optimum recording current is obtained for different magnetic head pairs in both modes.

Further, in the insert mode in which the once recorded tape is recorded while being erased by the magnetic heads 9 and 10, a method of increasing the recording current as compared with the normal recording state is used. In this case, the gain switching circuit 14 increases the recording current.

Note that reference numeral 15 is an external mode switching signal for switching the gain of the gain switching circuit according to the use mode.

FIG. 9 is a specific example of the recording current characteristics of the magnetic heads 9 and 10. ("VTR" by Kenichi Sawasaki, Sho 46.10.Corona Publishing, P49, Figure 4.
See 12). In FIG. 9, the horizontal axis represents the recording current and the vertical axis represents the reproduction output level. It can be seen from FIG. 9 that the recording current affects the reproduction output level and frequency characteristics of the magnetic heads 9 and 10. Therefore, if the recording current deviates from the optimum recording current, the S / N of the recorded / reproduced image of the VTR deteriorates. The characteristics shown in FIG. 9 differ depending on the standard mode, the triple mode, and the insert mode as described above.

As described above, when the recording current deviates from the optimum recording current,
Since the S / N of the recorded / reproduced image of the VTR deteriorates,
In R, the recording currents of the magnetic heads 9 and 10 are adjusted by the level adjusters 4 and 7, so that the FM modulation circuit 3, the mixing circuit 5, the low frequency conversion circuit 6, the gain switching circuit 14 and the recording operation. Variations in the gain of the amplifier circuit 8 and variations in the recording current caused by variations in the level of the input video signal a are absorbed.

This adjustment adjusts the level adjuster 4 so that the voltage drop across the resistor 13 at the output terminal 12 becomes the optimum value for the magnetic head used for the brightness signal b. In addition, for the color signal, in order to prevent the diamond cross beat interference, the level adjuster 7 is set so that the recording current is usually about 10 dB lower than the recording current level of the luminance signal in the state where the luminance signal is excluded. Make adjustments.

Therefore, in the conventional VTR having the above-mentioned configuration, it is necessary to adjust the recording current of the luminance signal and the chrominance signal, and the variable resistor is used for this adjustment. Had the drawback of having

An example of the circuit for adjusting the recording current is described in Masakazu Hara and Saburo Takahashi, "Small VTR", Sho 47.3, Japan Broadcasting Corporation, P23.

(Object of the Invention) An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to adjust the recording currents of the luminance and chrominance signals regardless of switching use of magnetic head pairs having different track widths or mode switching such as insert. Another object of the present invention is to provide a magnetic recording / reproducing apparatus which is unnecessary.

(Summary of the Invention) The present invention supplies an FM-modulated luminance signal to a variable gain amplifier circuit whose gain changes with an input control signal, while a low-frequency converted chrominance signal is fed back to the output to output a burst. It is supplied to a color signal automatic gain control circuit (hereinafter abbreviated as "chroma AGC circuit") that controls the level to a certain constant value, so that the level is always kept
The brightness output of the variable gain amplifier circuit and the color output of the chroma AGC circuit are mixed by a mixing means and supplied to the magnetic head, and a brightness recording current signal flowing in the magnetic head is detected, and the detection signal is Negative feedback control is performed on the variable gain amplifier circuit via the gain switching circuit of No. 2, and the first gain switching circuit is connected to a position from the subsequent stage of the chroma AGC circuit to the magnetic head. By switching the gain of the gain switching circuit of No. 2 according to the mode switching signal, the recording current of the FM luminance signal and the low frequency conversion color signal flowing in the magnetic head is always controlled to be constant, and the recording current adjustment is unnecessary. There are features.

(Embodiment of the Invention) An embodiment of the present invention will be described below with reference to FIG. First
In the figure, 16 is a variable gain amplifier circuit whose gain is variable according to an input control signal 17, 18 and 19 are first and second gain switching circuits whose gains are switched according to the mode switching signal 15, respectively. Is a sync period level detection circuit for detecting and outputting the output level of the second gain switching circuit 19 in the sync period by the input sync separation signal 29, 21 is a comparison circuit, 22 is a reference voltage source, and 30 is a detection circuit. is there.

Further, 23 is a variable gain amplifier circuit 24 similar to the variable gain amplifier circuit 16, a burst level detection circuit 25 for detecting a burst level from the input low frequency conversion color signal, a comparison circuit 2.
6. A chroma AGC circuit including a reference voltage source 27 and a detection circuit 28. Further, the same or equivalent parts as those in the conventional example are designated by the same reference numerals.

Next, the operation of this embodiment will be described. Video signal a to LPF1
The brightness signal b separated by is FM-modulated by the FM modulation circuit 3. Then, it is input to the variable gain amplifier circuit 16 and amplified by the circuit 16 with a gain according to the input control signal 17. Next, the FM luminance signal output from the circuit 16 is mixed by the mixing circuit 5
Is mixed with the low-pass conversion color signal which is the output of the chroma AGC circuit 23. After that, the magnetic head 9,
Supplied to 10.

The recording current flowing through the magnetic head 9 is detected by the resistor 13. The detected current signal is amplified by the second gain switching circuit 19 with a constant gain determined according to the mode switching signal 15,
It is supplied to the synchronization period level detection circuit 20.

The synchronization period level detection circuit 20 detects the level of the input detection current signal during the synchronization period based on the supplied synchronization separation signal 29. Since the detected current signal in which the FM luminance signal and the low-frequency conversion color signal are mixed has only the FM luminance signal in the synchronization period, the synchronization period level detection circuit 20 detects the FM luminance from the input detection current signal. Only the level of the signal will be detected.

Further, the output of the synchronization period level detection circuit 20 is negatively fed back as a control signal 17 to the variable gain amplification circuit 16 via the comparison circuit 21 and the detection circuit 30, and is the input of the comparison circuit 21.
The FM luminance signal level is controlled so as to be always maintained at a certain level corresponding to the reference voltage source 22.

In other words, the input signal of the comparison circuit 21 is the magnetic head 9
The FM luminance current signal flowing to the magnetic head 9 is a signal amplified by the gain of the second gain switching circuit 19 and flows to the magnetic head 9.
The FM luminance current signal is always held at a constant level regardless of the level fluctuation of the luminance signal b in the video signal a or the gain variation of the FM modulation circuit 3, the mixing circuit 5, and the recording amplification circuit 8. It is possible to eliminate the need for the adjustment by the variable resistor as described above.

Moreover, by switching the gain of the second gain switching circuit 19 by the mode switching signal 15, the optimum FM luminance recording current is supplied to the magnetic head pairs provided with different track widths according to the tape running speed. can do. In insert mode, only a certain level
FM luminance recording current can be increased.

On the other hand, the color signal C separated from the video signal a by BPF2
Is converted to low frequency by the low frequency conversion circuit 6 and then chroma AGC
It is supplied to the circuit 23.

In the chroma AGC circuit 23, the level of the burst period in the low frequency conversion color signal output from the circuit 23 is detected by the burst level detection circuit 25, and a signal corresponding to the burst period level is supplied to the comparison circuit 26. To be done. Then, the output of the comparison circuit 26 passes through the detection circuit 28 and the variable gain amplification circuit.
Negative feedback to 24. As a result, the level of the color signal output during the burst period of the chroma AGC circuit 23 becomes the reference voltage source 27.
It is controlled so that it is always maintained at a certain constant level according to.

Next, the output of the chroma AGC circuit 23 is supplied to the first gain switching circuit 18 and is amplified by a constant gain determined according to the mode switching signal 15. After that, the FM luminance signal output from the variable gain amplifier circuit 16 is mixed in the mixer circuit 5, and the magnetic head is passed through the recording amplifier circuit 8 having a constant gain.
Supplied to 9,10.

Therefore, the level variation of the color signal c in the input video signal a and the gain variation of the low frequency conversion circuit 6 are caused by the above-mentioned chroma AG.
The low-frequency conversion color signal having a substantially constant level is absorbed by the C circuit 23 and supplied to the magnetic head. Moreover, by switching the gain of the first gain switching circuit 18 by the mode switching signal 15, as in the case of the luminance signal described above, it is optimal for magnetic head pairs provided with different track widths according to the tape running speed. The color signal recording current can be supplied, or the color signal recording current can be increased by a certain level in the insert mode.

Further, when the gain of the first gain switching circuit 18 is increased (or decreased) in accordance with the mode switching signal 15, the second gain
The gain switching circuit 19 is configured to decrease (or increase) the gain of the first gain switching circuit 18 by the increment (or decrease). Further, in the configuration of this embodiment,
As described above, the variable gain amplification circuit 16, the mixing circuit 5, the recording amplification circuit 8, the second gain switching circuit 19, the synchronization period level detection circuit 20, the comparator 21, and the detection circuit 30 enable the synchronization period level detection circuit 20 to operate. Since the input luminance signal level is always controlled to be constant, the smaller (or larger) the gain of the second gain switching circuit 19 is, the larger (or smaller) the FM luminance recording signal flowing through the resistor 13.

In the above description, parentheses are intended to be selected within parentheses.

Therefore, the color signal recording current increases by the gain increase of the first gain switching circuit 18, and the luminance recording current increases by the gain decrease amount of the second gain switching circuit 19, and the same amount is recorded in both. The current can be increased.

Contrary to the above, when the gain of the first gain switching circuit 18 is reduced, the chrominance signal recording current is reduced by the gain reduction amount and the luminance recording current is increased by the second gain switching circuit 19. Therefore, both can reduce the recording current by the same amount.

Although the current flowing through the magnetic head 9 is detected in the embodiment shown in FIG. 1, there is no difference between the magnetic heads 9 and 10 even if it is detected from the magnetic head 10, and it goes without saying that the same applies. . In the embodiment shown in FIG. 1, since the luminance signal is extracted from the recording current signal flowing through the resistor 13, the synchronization period level detection circuit 20 detects the luminance signal level only during the synchronization period. As a second gain switching circuit 19
It is obvious that the same effect can be obtained even if an HPF is provided at the input end of and the color signal converted to the low frequency range is removed.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, parts that are the same as or equivalent to those in FIG. 1 are given the same reference numerals. This embodiment differs from the first embodiment in that the first gain switching circuit 18 is provided between the mixing circuit 5 and the recording / amplifying circuit 8.

If the variation of the circuit gain is converted into the input fluctuation of the variable gain amplifier circuit 16 and expressed, the FM luminance recording current is constant within a certain fluctuation range 31 of the input of the variable gain amplifier circuit 16 as shown in FIG. Controlled by level. However, since the input range 32, 33 exceeds the gain change range of the variable gain amplifier circuit 16, the luminance recording current is not controlled to a constant level. Therefore, when the gain of the second gain switching circuit 19 is switched according to the mode switching signal 15, in the embodiment shown in FIG. 1, the operating point of the control characteristic deviates by the switched gain 34, that is, The operating point shifts from 31a to 31b, and one of the controllable ranges for the input fluctuation of the variable gain control circuit 16 becomes narrow.

However, in the embodiment shown in FIG. 2, the mode switching signal 15
Even if the gains of the first and second gain switching circuits 18 and 19 are switched in accordance with the above, the gains of the variable gain amplifying circuit 16 do not change because the gains of the two gains increase or decrease by the same amount in the opposite directions. The operating point of does not change. Therefore, the second embodiment has an effect that the maximum control range can always be obtained regardless of the mode change.

FIG. 4 shows a specific example of a circuit diagram suitable for integrating the present invention shown in FIG. In FIG. 4, 35 is an integration range, 36 is a control signal for selecting magnetic heads having different track widths provided according to the tape running speed, 37 is a control signal for identifying the insert mode, and 38 is both of the above control signals.
A gain switching signal generating circuit for generating a control signal for switching the gains of the first and second gain switching circuits 18 and 19 to three stages by being supplied with 36, 37, 39 is an FM luminance signal, and 40 is a low-pass converted color. It is a signal.

Of the outputs 41, 42 and 43 of the gain switching control signal generating circuit 38, only one of them is a control output and the other two are at a high level. Therefore, the gain of the first gain switching circuit 18 is as follows according to the input control signals 36 and 37.

The gain of the second gain switching circuit 19 is as follows.

Here, as each of the resistance _{values, R 44 + R 45 = R} 47 + R 48 = R 49 + R 50 = R 46 = R 53 R 51 + R 52 = R 54 + R 55 = R 56 + R 57 = R 46 = R 53 R The effect of the present invention can be obtained by setting to satisfy ₄₅ × R ₅₂ = R ₄₈ × R ₅₅ = R ₅₀ × R ₅₇ .

Further, FIG. 5 shows a specific example of a circuit diagram suitable for integrating the present invention shown in FIG. This specific example is the same as the circuit shown in FIG.
The same effect as described in (Fig.) Can be obtained.

Next, a time chart of the input control signals 36, 37 and the outputs 41, 42, 43 of FIGS. 4 and 5 is shown in FIG.

As is clear from the figure, any one of the outputs 41, 42 and 43 can be set to the low level by the combination of the high and low of the input control signals 36 and 37.

Further, FIG. 7 shows a concrete circuit example of the gain switching control signal generating circuit 38 for obtaining the above-mentioned input / output signal waveform.

The operation of the circuit is obvious to those skilled in the art, and therefore its explanation is omitted.

(Effects of the Invention) As described above, according to the present invention, the recording current flowing through the magnetic head can be automatically maintained at a constant level regardless of variations in circuit gain and level fluctuations of the input video signal. It is possible to eliminate the need for adjusting the recording current. Therefore, it is possible to reduce the expensive variable resistor for adjustment, and it is possible to realize the elimination of the adjustment process which requires manpower and causes a large cost increase.

Further, there is an effect that the range in which the automatic control is possible can be obtained to the maximum.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, FIG. 3 is a characteristic diagram of a variable gain amplifier circuit, and FIGS. Figure is Figure 1, respectively
FIG. 6 is a diagram showing a specific circuit example of the present invention shown in FIG.
FIG. 7 is a time chart showing the input control signal and output waveforms of FIGS. 4 and 5, FIG. 7 is a circuit diagram showing one specific example of the gain switching control signal generation circuit of FIGS. 4 and 5, and FIG. FIG. 9 is a block diagram showing an example, and FIG. 9 is a diagram for explaining the characteristics of the magnetic head. 3 ... FM modulation circuit, 5 ... Mixing circuit, 6 ... Low frequency conversion circuit, 9,10 ... Magnetic head, 18,19 ... First and second gain switching circuit, 16 ... Variable gain amplification Circuit, 15 …… Mode switching signal, 20 …… Synchronous period level detection circuit, 23 …… Chroma AGC
Circuit, 30 ... Detection circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunsuke Mibayashi, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside Home Appliances Research Laboratory, Hitachi, Ltd. (72) Inventor Masahiro Sasaki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa (56) References Japanese Unexamined Patent Publication No. 58-129893 (JP, A) Actual development No. 58-116369 (JP, U)

Claims (4)

[Claims] 1. A modulation means for FM-modulating a luminance signal, a low-frequency conversion means for converting a color signal into a low frequency band, and a burst period level of a signal supplied from the low-frequency frequency conversion means, which is controlled to be constant and output. Color signal automatic gain control means, variable gain amplification means for amplifying the signal supplied from the modulation means with a gain according to an input control signal, output signal of the variable gain amplification means, and the color signal automatic gain control means Of the signal passing through the magnetic head, the recording amplifying means for supplying the signal passing through the mixing means to the magnetic head, the current detecting means for detecting the signal current flowing through the magnetic head, and the current detecting means. Second gain switching means to which an output is input, and the second gain switching means
After comparing the luminance signal output of the gain switching means with a reference voltage source for detection, the comparison detection means for supplying the variable gain amplification means as the input control signal, and the magnetic head from the latter stage of the color signal automatic gain control means And a first gain switching means connected between the first and second gain switching means, and the gains of the first and the second gain switching means can be externally interlocked and switched according to a mode switching signal. And a magnetic recording and reproducing device. 2. The magnetic recording / reproducing according to claim 1, wherein the first gain switching means is connected between the color signal automatic gain control means and the mixing means. apparatus. 3. The magnetic recording / reproducing apparatus according to claim 1, wherein the first gain switching means is connected between the mixing means and the amplifying means. 4. The gains of the first and second gain switching means are increased and decreased in opposite directions in response to the mode switching signal from the outside.
The magnetic recording / reproducing apparatus according to the second or third aspect.