JPH0832015B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus for recording and reproducing a video signal, and more specifically, for separating a video signal into a luminance signal and a color signal. If the amplitude of the sync signal contained in the luminance signal shrinks to an unsatisfactory size (hereinafter referred to as sync shrinkage) during each processing, the sync shrinkage is corrected. The present invention relates to a magnetic recording / reproducing apparatus including a means for doing so.

[Background of the Invention]

Conventionally, there are many documents regarding signal processing in a magnetic recording / reproducing apparatus (for example, "Home VTR Primer", Corona, Showa 5).
First issue in 6 years, published by Katsuya Yokoyama et al., P150-P164).

As is clear from these documents, in the magnetic recording / reproducing apparatus, various signal processing and operation control are performed with the sync signal included in the video signal as a reference, and a sync signal with an appropriate amplitude is generated. It is absolutely necessary to secure it. If the sync signal shrinks and a sufficient amplitude cannot be obtained, the operation of the drive servo system such as the rotary magnetic head device or the tape running system is likely to be disturbed, or the malfunction of the color signal processing operation is caused. There is a case where N is deteriorated, or an extremely synchronized flow occurs and the image quality is significantly deteriorated.

Especially for portable VTRs and camera-integrated VTRs that require low power consumption, lower power supply voltage is being promoted.
For example, measures have been taken to secure a dynamic range by using a larger number of clamp circuits than in the past, and therefore, there is a tendency that synchronization shrinkage is more likely to occur in the signal processing circuit.

For this reason, in the magnetic recording / reproducing apparatus, it is necessary to correct the synchronization shrinkage of the synchronization signal included in the video signal.

[Object of the Invention]

An object of the present invention is to provide a magnetic recording / reproducing apparatus which can solve the problem of synchronization shrinkage in the prior art as described above, and which has a circuit structure with good cost performance and which is capable of compensating for the shrinkage of the synchronization signal. It is in.

[Outline of Invention]

The feature of the present invention is that the reproduced video signal is clamped and processed at the tip of the sync signal from the viewpoint of securing the dynamic range, and corresponds to the amplitude portion of the sync signal in the clamped video signal (luminance signal). A non-linear amplifier circuit that increases the gain of the DC level more than the gain of the amplitude portion of the video signal (luminance signal) is used as a synchronous expansion signal generation circuit, and some of the constituent elements of the luminance / color signal mixing circuit are shared. However, by adding the expanded sync signal from the sync expanded signal creating circuit to the mixed output by the luminance / color signal mixing circuit, the dynamic range of the reproduction processing circuit up to the preceding stage is impaired. Instead, the amplitude expansion processing is applied only to the synchronization signal to realize a video signal having a synchronization signal with an appropriate amplitude.

Example of Invention

Hereinafter, the present invention will be described with reference to examples. FIG. 1 is a block diagram showing a system configuration of one embodiment of the present invention.

In FIG. 1, 1 is an input terminal for a composite video signal, 2 is an AGC amplifier for adjusting the level of the input video signal to a constant value, 3 is a recording brightness comb filter for extracting only a brightness signal from a high frequency signal, and 4 is a recording brightness comb filter. Low-pass filter (hereinafter abbreviated as LPF) for limiting the unnecessary band, 5 is a clamp circuit that fixes the DC level of the video signal at the peak potential of the synchronizing signal, 6 is an emphasis circuit, and 7 is the video level below a specified value. Clip circuit to suppress, 8 is an angle modulation circuit, 9 is a recording amplifier, 10 is a video head, 11 is a magnetic tape, 12 is a sync separation circuit for extracting only the sync signal from the video signal, 13 is the level of the video signal, AGC detection circuit that controls the gain of AGC amplifier 2 by, 14 is a preamplifier, 15 is an AGC amplifier for adjusting a plurality of head output signals (Y _EM ) to constant values, 16 is a reproduction FM equalizer, and 17 is an inversion Suppression circuit, 18 is FM
Demodulation circuit, 19 is a de-emphasis circuit, 20 is a video signal
A clamp circuit that fixes the DC level at the apex potential of the sync signal, 21 is a noise cancel circuit that suppresses high-frequency, small-amplitude signals, 22 is a sync expansion signal creation circuit that expands only the sync signal amplitude of the video signal, 23 Is a luminance / color signal mixing circuit that mixes the reproduction luminance signal and the reproduction chroma (color) signal, 24
Is a switching circuit for recording / reproducing, 25 is a video amplifier for amplifying and outputting a video signal to an appropriate level, 26 is an output terminal for a composite video signal, and 27 is an input terminal for a reproduction chroma signal.

In the signal circuit block diagram of FIG. 1, during recording,
The video signal input from the terminal 1 is sent from the AGC amplifier 2 to the unillustrated television receiver or the like via the changeover switch 24, the video amplifier 25, and the output terminal 26, while being passed through the circuits 3 to 9 to the video head 10. Then, the luminance signal and the color signal are recorded on the magnetic tape 11 in a separated form.

At the time of reproduction, the changeover switch 24 is switched to the side of the broken line, the luminance signal reproduced by the head 10 from the magnetic tape 11 is processed by passing through various circuits 14 to 21, and then synchronized by the sync expansion signal creation circuit 22. Only the amplitude of the signal is particularly expanded, and then the mixed circuit 23 reproduces the reproduced chroma signal and the reproduced luminance signal separately input from the terminal 27 and mixed with the expanded output from the synchronous expanded signal generating circuit 22. A signal is added and sent to the television receiver or the like via the changeover switch 24, the video amplifier 25, and the output terminal 26.

The circuit configuration shown in FIG. 1 shows the configuration of a VTR, but the operation of each circuit therein is known, except for the synchronous decompression signal generation circuit 22, and is not directly related to the present invention. However, they are not detailed here. Further, chroma signal processing, servo control and the like are also known and are not shown in FIG. 1 because they are not directly related to the present invention. The feature in FIG. 1 is that a synchronous expansion signal generating circuit 22 is provided.

As can be understood from the part shown in FIG. 1, a video signal is recorded on the magnetic tape 11, further reproduced, and output as a reproduced video signal, which passes through many processing circuits.
Various processes are performed by these processing circuits. As a matter of course, these processing circuits must have good linearity between input and output signals. However, the linearity of the video signal deteriorates not a little while passing through many processing circuits. In particular, the sync signal is the basis of signal processing and control, and the contraction of the sync signal causes various problems as described above. In particular, a clamp circuit is often provided on the reproducing side to secure the dynamic range, which causes the sync signal to shrink. As the power supply voltage becomes lower, the synchronization shrinkage becomes more severe. Therefore, in order to compensate for this, the sync expansion signal generating circuit 22 is inserted in the final stage on the reproducing side.

In FIG. 1, the sync expansion signal generating circuit 22 is provided at the final stage on the reproducing side, but it is not necessarily limited to the position shown in FIG. However, it is advantageous to provide the final stage on the reproducing side as shown in FIG. 1 for the following reason.

(A) Synchronous contraction may occur in any of the recording and reproducing processing circuits. In particular, the clamp circuit is highly likely to cause synchronization shrinkage. For example, assuming that there is a 5% synchronization shrinkage per clamp circuit, and if a total of 5 clamp circuits are passed during recording / reproduction, the synchronization signal will be normal. 3 /
It is a problem because it is lowered to the level of 4. Also, FM
There is a high possibility that synchronization contraction will occur due to the deterioration of the linearity of the modulator / demodulator. Therefore, it is preferable that the final processing stage on the reproducing side comprehensively corrects the synchronizing signal to have an appropriate amplitude.

(B) The greater the number of circuits that exist after the synchronous expansion signal generation circuit until the video output, the more likely the synchronous contraction will occur again. In addition, since the composite video signal after the addition (mixing) of the luminance signal and the color signal has the color signal below the pedestal level, when the synchronous expansion is performed, the color signal is expanded together with it, which is a problem. There is. Therefore, it is preferable that the synchronous expansion signal generating circuit is provided in the final stage (before the stage of mixing with the color signal) of the luminance signal processing circuit.

(C) Providing the synchronization expansion signal generation circuit in the middle of the signal processing process leads to reducing the margin of the dynamic range of the circuits thereafter. Therefore, in order to secure the dynamic range, it is preferable to provide the synchronous expansion signal generating circuit at the final stage of the signal processing process.

FIG. 2 shows a concrete circuit example of the synchronous expansion signal generating circuit used in the present invention.

In the block diagram of FIG. 1, the sync expansion signal generating circuit 22 and the mixing circuit 23 are clearly separated. However, in the concrete circuit example shown in FIG. 2, the two are clearly separated. Since it is difficult, both are integrated and shown as a block S surrounded by a broken line.

In FIG. 2, 51 is the noise canceling circuit 21 of FIG.
The reference numeral 52 is an input terminal for the signal output from the output terminal, 52 is an output terminal of the luminance / color signal mixing circuit 23, and 27 is a chroma (color) signal input terminal.

The features of the circuit of FIG. 2 are, as already described, the synchronous expansion signal generating circuit 22 and the luminance / color signal mixing circuit in FIG.
The point is that by configuring 23 in an integrated manner, it is possible to provide a synchronous expansion signal generation circuit with little variation and good cost performance.

That is, in FIG. 2, transistors Q560, Q561, Q562
The differential amplifier M composed of the resistors R556, R557, and R558 is a luminance / color signal mixing circuit, and includes transistors Q555, Q556, and Q557.
The differential amplifier P including the resistors R553 and R556 is a synchronous expansion signal generating circuit, and both circuits have the load resistor R556 in common.

The luminance signal clamped to the sync signal tip potential by the clamp circuit 20 and the noise component suppressed by the noise cancel circuit 21 is input to the input terminal 51. The input luminance signal is guided to the bases of the transistors Q555 and Q560 via the emitter follower formed of the transistor Q554.
Transistor Q560 is transistor Q561, emitter resistance R5
57 and load resistor R556 form a linear differential amplifier. Further, the transistor Q562 also forms a linear differential amplifier with the transistor Q561, the emitter resistor R558, and the load resistor R556.

The luminance signal described above is led to the base of the transistor Q560, and the color signal input from the color signal input terminal 27 is led to the base of the transistor Q562. A DC potential is applied to the base of the transistor Q561.

As described above, the composite video signal in which the luminance signal and the color signal are mixed is taken out from the load resistor R556 and supplied to the terminal 52.

On the other hand, the transistor Q555 constitutes a differential amplifier together with the transistor Q556. However, this amplifier is a non-linear amplifier that amplifies the amplitude portion of the synchronizing signal contained therein with respect to the input luminance signal but does not amplify the luminance signal itself.

The amplification characteristic of this nonlinear amplifier will be described below with reference to FIG.

For example, the tip of the sync signal is at the base of the transistor Q555.
It is assumed that the signal I in which V ₁ is clamped is input. This time,
Setting the base potential of the transistor Q556 to the same V ₂ and the potential V ₂ of the pedestal portion of the input signal I, if the input signal I is greater than V ₂ (i.e. the amplitude part of the luminance signal itself) transistor Q556 is OFF, Transistors Q560, Q56
It does not affect the mixing circuit M composed of 1, Q562 and operates linearly as the linear characteristic Q ₁ shown in FIG.

However, when the input signal is smaller than V ₂ (that is, the amplitude part of the synchronization signal), the transistor Q556 also turns on, and the current Δi ₀ flowing in the collector of the transistor Q556 eventually becomes (However, R _E is the resistance value of the resistor R553).

The current Δi ₀ flowing through the collector of the transistor Q556 also increases the current flowing through the load resistance R _L by Δi ₀ , which causes the video signal output from the output terminal 52 to be ΔV = Δi ₀ × R _L (however, _RL becomes a signal in which the synchronizing signal amplitude of the input signal I is expanded by the load resistance R556).

That is, in FIG. 3, the synchronization signal amplitude of the input signal I has a non-linear characteristic Q2 (Q2 is a straight line Q3, which is a broken line on the extension of the straight line Q1).
However, the amplitude is expanded by ΔV and the amplitude is expanded by ΔV.

Therefore, the output signal U with respect to the input signal I has a waveform in which only the amplitude portion of the synchronizing signal is expanded by ΔV as compared with U ′ in the case where the nonlinear amplification is not performed.

For example, if the total sync shrinkage of recording and reproduction is 10% of the proper level, the sync expansion signal generating circuit of the present invention may correct 10%. That is, Because The resistance value should be selected for the relationship.

From the above, the characteristics of the specific circuit example shown in FIG. 2 will be understood.

FIG. 4 shows another specific circuit example of the main part S in FIG. The circuit shown in FIG. 4 is characterized in that the emitter of the transistor Q556 is provided with a current source composed of a transistor Q601 and a resistor R601. By doing this, transistor Q556
Does not turn ON / OFF, the input / output straight line Q2 shown in Fig. 3
The transition from linear to nonlinear can be made more gradual.

That is, the closer to the tip of the sync signal amplitude, the higher the amplification rate (expansion rate), and the less the extent to which the luminance signal itself is adversely affected by the sync extension.

FIG. 5 shows a more specific circuit example of the main part S in FIG. The circuit of FIG. 5 is characterized in that instead of the transistors Q555 and Q556 and the resistor R553 of FIG.
604, a resistor R604 and a diode D605 are provided to perform synchronous extension. The same effect can be obtained by this circuit.

〔The invention's effect〕

According to the present invention, in a magnetic recording / reproducing apparatus, a DC potential to be taken by a sync signal in an input luminance signal is set in advance, and a non-linear amplification for increasing an amplification gain only in a sync signal amplitude portion equal to or lower than the set DC potential. Circuit, the input luminance signal is amplified by the non-linear amplification circuit to create a decompressed synchronization signal, and the decompressed synchronization signal from the non-linear amplification circuit is added to the mixed output by the luminance / color signal mixing circuit. Since the composite video signal in which the amplitude expansion processing is performed only on the synchronization signal can be obtained by adding the synchronization signal, there is an advantage that the synchronization signal having a predetermined amplitude or more can be always secured and the reliability of the operation can be maintained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of an embodiment of the present invention, FIG. 2 is a circuit diagram showing a concrete circuit example of a main part S in FIG. 1, and FIG. 3 is a synchronous expansion circuit in FIG. FIG. 4 is a characteristic diagram showing the input / output characteristic of FIG. 4, and FIG. 4 is a main part S in FIG.
FIG. 5 is a circuit diagram showing another specific example of FIG. 5, and FIG. 5 is a circuit diagram showing still another specific example. DESCRIPTION OF SYMBOLS 1 ... Video signal input terminal, 10 ... Magnetic head, 11 ... Magnetic tape, 20 ... Clamp circuit, 22 ... Synchronous expansion signal creating circuit, 23
... Brightness / color signal mixing circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Asami Kuroyanagi 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Nikkei Video Engineering Co., Ltd. (72) Akira Shibata 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Within Tachi Video Engineering Co., Ltd. (56) References Showa 50-65320 (JP, U) Showa 60-186765 (JP, U) Showa 58-3678 (JP, U) Showa 57-69358 (JP, U)

Claims (2)

[Claims] 1. At the time of recording, a video signal is separated into a luminance signal and a chrominance signal for recording respectively, and at the time of reproduction, the reproduced luminance signal and chrominance signal are processed through respective processing circuits, and then the luminance / color signal is processed. In a magnetic recording / reproducing device mixed and used in a color signal mixing circuit, a reproduced luminance signal is taken in, only a synchronizing signal included in the luminance signal is amplified, and the luminance signal is not amplified. A non-linear amplifier circuit of the type is configured as a synchronous expansion signal generation circuit in such a manner that a load resistor which is a part of a constituent element of a brightness signal processing circuit including the brightness / color signal mixing circuit is shared, A magnetic recording / reproducing apparatus, wherein an output from a processing circuit is added with a sync signal expanded from the sync expansion signal generating circuit and used. 2. The magnetic recording / reproducing apparatus according to claim 1, wherein the sync / expansion signal generating circuit corresponds to the last stage of the reproduction luminance signal processing circuit.
A magnetic recording / reproducing apparatus provided on the input side of a color signal mixing circuit.