JPS6042523B2 - Magnetic recording device for luminance signals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a VTR (magnetic recording and reproducing device) that
This is an attempt to improve the recording characteristics.

(VTR) Particularly in general-use VTRs, during recording, the luminance signal is converted to an FM signal and recorded on a magnetic tape, and during playback, the reproduced FM signal is set to a constant amplitude by a limiter and then converted back to the original luminance signal. It has recovered to .

However, such a recording/reproducing method has the following drawbacks.

That is, FIGS. 1B-F show the magnetic tape 1 and the magnetic head 2 viewed from the width direction of the tape 1, and 2G
is the working gap of head 2.

Then, the head 2 receives a rectangular wave signal Ba as shown in FIG. 1A.
When the signal Ba is supplied, the signal Ba has already risen, so as shown in FIG. It is formed. During the period, since the head 2 moves in the direction of arrow 8, the magnetized region 3A becomes a substantially oval region extending in the length direction of the tape 1, as shown in FIG. 1c. Become.

In this case, the polarity of the magnetic pole in the region 3A corresponds to the polarity of the signal Ba, for example, as indicated by the arrow 4A. Next, when the signal Ba falls immediately, as shown in FIG. 1D,
A substantially circular magnetized region 3B is formed.

That is, the signal Ba indicates the time point. Since the polarity is suddenly reversed, the end of area 3A (right end in the figure) is area 3
At this time, since the polarity of the signal Ba is reversed, the polarity of the magnetic pole in the region 3B becomes the opposite polarity to that in the region 3A, as shown by an arrow 4B. During the period 1 to 2, the head 2 moves in the direction of the arrow 8, so the area 3B becomes a substantially oval area as shown in FIG. 1E.

Furthermore, when the signal Ba rises immediately, the period changes from 3 to
Z, as shown in FIG. 1F, a magnetized region 3C similar to the magnetized region 3A is formed following the magnetized region 3B.

Thereafter, similarly, magnetized regions 3 are sequentially formed at a pitch corresponding to the frequency of the signal Ba and in a size corresponding to the level of the signal Sa, and the signal Sa is stored.

On the other hand, in a VTR, when a luminance signal is converted into an FM signal during recording, as shown in FIG. 2A, when the luminance signal Sy (Ph is a horizontal synchronizing pulse) is at the black level,
The frequency of the M signal is low and becomes high when the white level is reached. The FM signal is also generally a rectangular wave signal. Therefore, as shown in FIG. 2A, for example, a luminance signal S whose level changes rapidly from a black level to a white level.
If y is converted to an FM signal and recorded on tape 1,
A magnetized region 3 is formed as shown in FIG. 2B.

That is, when the luminance signal Sy is at the black level, the frequency of the FM signal is low, so the magnetized regions 3a to 3c at this time
are formed at equal intervals with a coarse pitch, and since the frequency of the FM signal is high when the luminance signal Sy is at the white level, the magnetized regions 3d to 3g at this time are formed at equal intervals with a fine pitch, and the head Since the recording current (FM signal) of No. 2 becomes smaller as the frequency becomes higher, the area of regions 3d to 3g becomes smaller. Therefore, the area 3c formed last when the signal Sy is at the black level has a smaller area occupied by the next area 3d, and therefore has a larger area than the areas 3a and 3b. When the magnetized regions 3 are formed in this way, the reproduction signal (F
M signal) Sf has a waveform as shown by a thick solid line in FIG. 2C (shown as a sine wave for simplicity).

That is, each half cycle 5a to 5g of the signal Sf is generated corresponding to the regions 3a to 3g, and at this time, the magnitude (level) of each half cycle 5a to 5g is different from the region 3a to 3g.
Corresponds to an area of 3g. Therefore, half cycles 5a and 5b occur with equal magnitude corresponding to regions 3a and 3b, and as shown by the thin solid line, the DC level (zero cross level) Edc of signal Sf is equal to the upper and lower half cycles 5a and 5b. It comes to the position where it is divided by area. However, region 3c is different from regions 3a, 3
Since the area is larger than b, the half cycle 5c corresponding to region 3c is larger, and this also causes the DC level E
dc also increases rapidly, and since the areas 3d to 3g have the same area, the DC level Edc decreases to a steady value.

At this time, half cycles 5d to 5g are vertically symmetrical with respect to this DC level EdC. Therefore, playback F
The M signal Sf has a waveform as shown in FIG. 2C. In a VTR, the reproduced FM signal Sf is set to a constant amplitude by a limiter, but if the level indicated by the broken line in FIG.
The M signal Sf becomes as shown in FIG. 2D, and the cycle 5
d disappears.

In this respect, the absence of the cycle 5d is equivalent to the fact that the frequency of the FM signal Sf has become lower, and this corresponds to the black level in terms of the luminance signal Sy. Therefore, when the FM signal Sf from the transmitter is FM-demodulated, black noise 7, so-called blackout, appears at the boundary of the luminance change from black to white on the playback screen 6, as shown in FIG. 2E. Noise 7 will be generated, and the quality of the reproduced image will be degraded. Therefore, ■TR, which does not generate the blackening noise 7, has been considered. Figure 3 shows an example of the VTR.
The luminance signal Sy is supplied to the FM modulation circuit 14 through the line from the input terminal 11 to the AGC amplifier 12 to the pre-emphasis circuit 13, and is converted into a rectangular wave FM signal Sf with a duty ratio of 50%, as shown in FIG. 4A. is,
This signal Sf is supplied to the differentiating circuit 15, and as shown in FIG. This is a bidirectional pulse Pfl, that is, a PFM pulse Pf.

This pulse Pf is then supplied to the rotating magnetic head 17 through the recording amplifier 16, and the pulse Pf is sequentially recorded on the magnetic tape 1 so that one field corresponds to, for example, one diagonal magnetic track. Note that the luminance signal recorded in this manner is reproduced in the same manner as a general VTR.

The luminance signal recorded in this manner does not generate blackening noise 7 during reproduction.

That is, as shown in FIG. 5A, when the luminance signal Sy suddenly changes from the black level to the white level (this is the second
(same as Figure A), in this TR, a sufficiently narrow PFM pulse Pf is recorded instead of the FM signal Sf, so the magnetized region 3 due to this pulse Pf is as shown in Figure 5B. , becomes almost circular, and the overlapping portion of region 3 becomes smaller or disappears compared to the case of FIG. 2B. In particular, when the luminance signal Sy is at the black level, the last area 3c is smaller than the area 3a even if the next area 3d is smaller.
, 3b. Therefore, such area 3
As shown in FIG. 5C, the reproduced FM signal Sf obtained from the reproduction FM signal Sf has a substantially constant DC level Edc, and each half cycle 5a to 5g is also substantially vertically symmetrical with respect to the time axis (horizontal axis).

Since the level indicated by the broken line is the reproduction system limiter level, the FM signal Sf from the limiter is as shown in Fig. 5D.
As shown in Figure 2D, the half cycle 5d does not disappear, and the FM signal S during recording
The FM signal Sf is the same as f.

Therefore, the blackening noise 7 does not occur on the screen reproduced from this FM signal Sf. Furthermore, as shown in FIG. 5B, since the overlapping portion of the magnetized regions 3 is small or non-existent, the pitch of the magnetized regions 3 can be reduced if the same characteristics as before are sufficient, and therefore recording is possible. Density can be increased.

By the way, in a general VTR, the recording amplifier 16 is configured as shown in FIG.
The FM signal Sf from 4 is supplied to the head 17 through the signal line of transistor Q1→transformer T1→cable F1→rotary transformer T2.

Therefore, in the VTR shown in FIG. 3 as well, it is conceivable to configure the recording amplifier 16 as shown in FIG. 6.

However, when the luminance signal Sy is converted into the FM signal Sf, its modulation characteristics are as shown in FIG. 7, for example, whereas in the amplifier 16 of FIG. The frequency characteristic of the recording current is as shown by the broken line in FIG. 7, and the recording current itself becomes difficult to be supplied to the head 17 for a signal component of a sufficiently high frequency.

Therefore, when the pulse Pf is amplified by the amplifier 16, the harmonic components of the pulse Pf, especially the third harmonic, are no longer recorded.In other words, the pulse Pf has a rough waveform, which causes black It becomes impossible to suppress the snoring noise 7. Furthermore, in this amplifier 16, as the recording current increases, the distortion rate characteristics tend to deteriorate and the second-order distortion tends to increase.

The existence of second-order distortion means that the waveform of the pulse Pf is rounded, which leads to the generation of blackening noise 7, and especially if the second-order distortion is within the band of the fundamental wave of the pulse Pf. This results in so-called overmodulation, which also causes darkening noise 7 on the screen 6.
Therefore, it is necessary that the second-order distortion is small, for example -4α
It is preferable that it is below B. Furthermore, in the amplifier shown in FIG. 6, as the recording current increases, the frequency characteristics and the like deteriorate.

In addition, since the head 17 is reactive, the head 17
In order to make the recording current constant, it is also necessary to correct the frequency characteristics. This invention attempts to eliminate the above problems.

Therefore, in the present invention, as shown in FIG. 8, for example, negative current feedback is provided to the recording amplifier 16 to
Let be a constant current amplifier.

That is, in this example, a common emitter transistor Q1, an emitter follower transistor Q2,
A pulse P from the differentiating circuit 15 is directly connected to the transistor Q3 whose emitter is grounded.
f is supplied to the collector of the transistor O,
Primary coil of transformer T1 and resistor R for recording current detection
A feedback resistor R2 is further connected between the emitter of the transistor Q1 and the resistor R1.

Further, a capacitor C1 and resistors R3 and R4 are connected to the primary coil of the transformer T1, and a capacitor C2 is connected in parallel to the resistor R2 to correct the frequency characteristics.

Note that the resistor R5 is for stabilizing DC by negative feedback. According to such a configuration, the pulse Pf is sequentially amplified by the transistors Q1 to Q3 and supplied to the head 17, and in this case, a part of the recording current is taken out by the resistor R1, and this is transferred to the transistor through the resistor R2. Negative feedback is provided to Q1. The bare gain of the amplifier 16 is about 6 B, and a negative feedback of about 38 (11 B) can be applied. As a result, the frequency characteristics of the amplifier 16 are extremely high, as shown by the solid line in FIG. The area becomes flat.

Further, the recording current of the head 17 also becomes a constant current due to negative feedback. Therefore, the pulse Pf is sufficiently recorded up to its harmonic components, that is, the pulse Pf is recorded without causing any waveform distortion, so that no blackening noise 7 is generated on the reproduction screen 6.

In addition, the distortion rate characteristics are also improved and no second-order distortion occurs in the pulse Pf, so the waveform distortion of the pulse Pf due to the second-order distortion is eliminated, and the blackening noise 7 due to the second-order distortion is also eliminated.

Furthermore, since overmodulation due to secondary distortion is also eliminated, blackening noise 7 due to this overmodulation is also eliminated. Further, there is no change in frequency characteristics due to the magnitude of the recording current, and uniform reproduced image quality can be obtained.

Thus, according to the present invention, it is possible to obtain a reproduced screen with extremely high image quality without blackening noise. Furthermore, if the same performance as the conventional one is sufficient, high-density recording is possible, and long-time recording and playback can be achieved with a small amount of tape used.

[Brief explanation of the drawing]

1 to 7 are diagrams for explaining this invention, and FIG. 8 is a connection diagram of an example of this invention. 14 is an FM modulation circuit, and 15 is a differential circuit.

Claims (1)

[Claims] 1. An FM modulation circuit that converts the input luminance signal into an FM signal, a differentiation circuit that differentiates the output of this FM modulation circuit, a recording amplifier that amplifies the output of this differentiation circuit, and a magnetic The output current of the recording amplifier is negatively fed back to the input side of the recording amplifier to cause the recording amplifier to drive the magnetic head at a constant current. A magnetic recording device for luminance signals with an additional compensation circuit.