JPH0481085A - Video type recorder - Google Patents

Abstract

PURPOSE:To improve the C/N of a regenerative signal and to improve the picture quality of a reproduced picture by obtaining the regenerative signal while increasing the number of rotations of a rotary head in the case of reproducing rather than the number of rotations in the case of recording and further matching a trace with a recording track. CONSTITUTION:Rotating means 9 and 10 to increase the number of rotations of a rotary head 7a in the case of reproducing rather than that in the case of recording, displacing means 8 and 11 to make the trace of the rotary head 7a in the case of reproducing coincident to the recording track on a magnetic tape Tp are provided. Namely, the number of rotations of the rotary head 7a in the case of reproducing is increased rather than that in the case of recording, and the level of the regenerative signal is enlarged. In this case, the output voltage of the rotary head in the case of reproducing is proportional to the change rate of magnetic flux density in the coil of the rotary head. Therefore, by increasing the number of rotations of the rotary head, the level of the regenerative signal is increased. Thus, the C/N of the regenerative signal is improved, and the highquality reproduced picture can be obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention employs, for example, an 8 mm video format,
The present invention relates to a video tape recorder (VTR) suitable for use in recording and reproducing.

[Summary of the invention] The present invention employs, for example, an 8 mm video format,
Regarding a VTR suitable for use in recording and reproducing, there is provided a rotating means for increasing the number of revolutions of the rotary head during reproduction than during recording, and a trajectory of the rotary head during reproduction to match the recording track on the magnetic tape. By providing a displacement means for moving the magnetic tape, the level of the reproduced signal obtained by tracing the magnetic tape is increased, and the C/N ratio is improved.

(Prior Art) Generally, a video signal is FM modulated and recorded on a magnetic tape or the like, and the frequency spectrum of a reproduced signal reproduced from this magnetic tape is shown in FIG.

So-called video noise is superimposed on this reproduction signal, and this video noise is modulation noise (a) caused by the roughness of the surface of the magnetic tape due to the particle size of the magnetic tape.
Sliding noise caused by the surface condition of the magnetic head 0)),
The total noise (C) consisting of the noise in the preamplifier (C)
d).

Here, in order to reduce the overall noise signal (d), that is, to improve the C/N ratio of the reproduced signal, miniaturization of the particle size of the magnetic tape, cleaning of the magnetic head with the tape,
Improvements have been made to the S/N ratio of preamplifiers. moreover,
In order to raise the level of the reproduction signal from the magnetic tape and improve the C/N ratio, the Hc (coercive force) of the magnetic material of the magnetic tape,
Efforts are being made to increase Br (residual magnetic flux density).

Also, as a means of reducing video noise, F of the video signal is
Signal processing means such as the well-known pre-emphasis, which deepens the modulation level in the high frequency range when converting into an M signal, and the non-linear emphasis, which records the video signal by increasing the level of only the small amplitude signal part via a non-linear circuit, are used. It is used.

[Problem to be solved by the invention]

However, in recent VTRs, it is desired to further reduce video noise, and in particular, when obtaining a playback signal from an 8 mm format magnetic tape, the tape width is narrower than the conventionally used format. Since the relative speed was slow, there was a problem that the S/N ratio deteriorated.

The present invention has been made in view of the above problems, and its purpose is to
An object of the present invention is to provide an excellent VTR that improves the C/N ratio of a reproduced signal obtained by tracing a magnetic tape on which a signal is recorded, and as a result, reproduces a high-quality reproduced video.

Means for Solving Problem C] The present invention provides a rotary head (7a) during playback, as shown in the video tape recorder of FIGS. 1 to 6, for example.
rotating means (9) for increasing the number of rotations of the camera from the time of recording;
(10), and displacement means (8) and (11) for matching the locus of the rotary head (7a) during reproduction with the recording track on the magnetic tape (Tp).

[Function] According to the VTR of the present invention, the rotation speed of the rotary head (7a) during playback is made faster than during recording, so the level of the playback signal increases, and in this case, the output voltage of the rotary head during playback is It is proportional to the rate of change of magnetic flux density within the coil of the rotating head. Therefore, increasing the rotation speed of yF will increase the level of the reproduced signal, and since video noise is relatively constant, the C/N ratio will improve.

〔Example〕

Hereinafter, embodiments of the VTR of the present invention will be described in detail with reference to the drawings.

In FIG. 1, (5) indicates a rotating drum, and this rotating drum (5) has rotating heads (7a) and (7b) for reproduction disposed 180 degrees opposite to each other, and this rotating head (7a). ) (7b) are provided with rotary transformers (not shown) connected to each of them.

Here, the rotating drum (5) is rotationally driven by a motor (9), and is controlled in a constant rotation closed loop by a rotation control section (10). Here, the running speed of the tape is constant, and the rotational speed of the rotary drum (5) is twice that during recording.

Further, approximately 1/2 of a magnetic tape Tρ, on which a video signal converted into an FM signal is magnetically recorded in advance, is wound around the rotating drum (5) so as to slide in a helical scan manner. In this case, a displacement means employing, for example, a dynamic tracking (DT) method is provided so that the locus of the rotary head (7a) coincides with the recording track on the magnetic tape Tp. This displacement means includes a piezoelectric element (8) to which a rotating head (7a) is fixed on a rotating drum (5), and a signal processing section (11) for supplying a signal to electrostrictively displace this piezoelectric element (8). It consists of.

This signal processing section (11) utilizes a well-known wop ring signal, and includes a piezoelectric element (
8) is attached, and a low frequency signal from a low frequency oscillator (12) is input to this piezoelectric element (8) via an adder (13) and a phase comparator (15). Further, the envelope detection signal of the reproduced signal supplied from the rotary head (7a) to the envelope detection circuit (18) is input to the phase comparator (15). The output signal from the adder (13) is supplied to the drive circuit (21), and the output signal from here is supplied to the piezoelectric element (8).

Furthermore, to the rotation tracing the magnetic tape Tρ, 7 degrees (
Respective reproduction signals from 7a) and 7b are supplied to preamplifiers (28a) and (28b) for predetermined amplification, and then a fixed contact (29a) of a changeover switch (29).

(29b). In this case, in the changeover switch (29), the movable contact (29c) is switched to the fixed contact (
29a), that is, the rotary head (7a) is always selected, and the reproduced signal S1 read by the rotary head (7a) is input to the demodulator (DME) (30).

Furthermore, the video signal output from the demodulation unit (DME) (30) is supplied to an A/D converter (31), where it is quantized and converted into a digital signal, which is stored in a frame memory (34). At this time, the period of the reproduction signal S1 is 1/2 of the recording signal at the time of recording. Here, the A/D converter (31
), a frame memory (34), and a D/A converter (36) are supplied with a clock signal of a predetermined period from a timing generator (38). The signal Sl is expanded twice and read out from the frame memory (34), and then D
The video output signal S is output from the /A converter (36).

Next, the operation in the above configuration will be explained.

First, the trajectory during recording on the magnetic tape Tp will be explained using FIG. For example, 17 in the NTSC system.
At time t1 when the recording head starts tracing during one field period of 60 seconds, the recording head moves to the magnetic tape Tp.
It is located at the lower part p, and from this position the dotted line part Tr1
At the time tz at the end of one field period after moving, it is located at the upper part p2. During this time, the magnetic tape Tp runs and moves by 121 minutes in the figure, and as a result, recording tracks Tr shown by solid lines are continuously recorded.

Here, the trajectory of the rotary head (7a) when it rotates at twice the speed and traces the recording track Tr recorded on the magnetic tape Tp will be explained using FIG. 3.

If the recording track T r z and the rotary head (7a) or (7b) are made to coincide with each other at the time tea shown in the figure, then at time t, which is 172 fields after time ttm, the dotted line portion Tr3 will be moved to the upper position p3. I will do it.

Therefore, the magnetic tape 'rp moves by 1/2f, (L), and the recording track Trz and the trace of the rotary head (7a) do not match. In other words, tracking deviation will occur.

Now to rotation, C (7a) is on the above recording track Trz
The alignment must be adapted to match and trace. The adaptation of this trace is the signal processing section (1
Based on the signal processing in step 1), the chip portion of the rotary head (7a) is moved in the track width direction by electrostriction of the piezoelectric element (8). In the signal processing section (11), a low frequency oscillator (12)
The low frequency signal from the piezoelectric element (
8) to drive and apply amplitude modulation to the reproduced signal, that is, to obtain a wappling signal. Then, the envelope of the reproduced signal S is detected by the envelope detection circuit (1
phase detection is performed using the signal supplied from the low frequency oscillator (12) which is input at the same time, and the recording track of the rotary head (7a) is A displacement (amount of deviation) with respect to Tr is detected. This displacement is applied from the adder (13) to the piezoelectric element (8) to automatically correct the position of the rotary head (7a) so that it coincides with the recording track Trz on the magnetic tape Tp.

In addition, instead of the above-mentioned wappling method, only a mechanical adjustment mechanism may be provided to simply change the angle of the locus of the rotary heads (7a) and (7b). The angle of the trace of the rotary head (7a), that is, the arrangement of the rotary head (7a) when the rotary drum (5) rotates at twice the speed will be explained.

Here, the video signal recording area width is lv, the longitudinal length of the video track is ft, and the magnetic tape Tp
The angle (recording angle) of the recording trunk Tr with respect to the longitudinal direction of the magnetic tape Tp is θ1, and the angle of the trajectory of the recording head (STILL angle) with respect to the longitudinal direction of the magnetic tape Tp is θ.

Then, , and furthermore, . And is expressed as. Therefore, when the rotary head (7a) has an arbitrary speed, the rotary head (7a) may be arranged so as to change the angle of the trajectory traced by 172 of the width of the recording track Trz.

The period of the reproduced signal S reproduced in this manner is 1/2 of the recording signal at the time of recording. Therefore, when reading, the period is doubled as shown in FIG. Here, the data w, ,W! ,W.

The reproduced signal S for one field consisting of V-BLK (blanking period) is sent to the demodulator (30) and the A/D converter (3).
1), and then stored in the frame memory (34), and thereafter, when reading from the frame memory (34), the time axes of each of the data W+, Wt, Wx, and SeaBLK are expanded by twice 79 Rr, Rz, R3,
The signal for one field consisting of V-BLK is read out. The thus obtained continuous signal on the time axis is output from the D/A converter (36) as a video signal output S3.

FIG. 6 shows another configuration example.

This example performs so-called TBC signal processing in which writing to or reading from the frame memory (52) is performed using separate clock signals CKS and CK6. Here, the clock signal CK5 is input to the timing generator (56).
A horizontal synchronization signal extraction circuit (57) is provided for extracting a horizontal synchronization signal as a reference for generating the horizontal synchronization signal, and from the horizontal synchronization signal extracted here, a write clock signal generation section (58) using, for example, PLL is provided. ) at clock signal CK
, is generated. This clock signal CK is supplied to the A/D converter (50) and the frame memory (52), and the digitized reproduction signal S is sent to the frame memory (52).
will be written to. Then, the frame memory (52) and the D/A are used to generate and read out the reproduced signal S written in the frame memory (52) into a signal expanded twice.
Clock signal CK supplied to the converter (54).

A reference signal is supplied to a read clock signal generation section (59), where it is generated and output at a predetermined period.

In this case, since TBC signal processing is performed, time axis fluctuations (jitter) are prevented.

In this way, the rotational speed of the rotary drum (5) during reproduction is doubled compared to that during recording, and the recording track T r
t and the trace are made to match. In this case, the output voltage of the rotary head (7a) is proportional to the rate of change of the magnetic flux density in the coil of the rotary head during tracing, that is, the number of turns of the coil is N, and the magnetic flux density passing through the coil is φ. Then, the output voltage e6 is expressed as follows. Here, the rotation speed of the rotating head (7a) is
For example, if it is doubled, the level of the reproduced signal (sl) will also be doubled.

Therefore, since the video noise is relatively constant, the C/N ratio of the resulting reproduced signal is improved.

It is clear that the present invention is not limited to the above-described embodiments, and that various changes can be made without departing from the gist of the present invention.

〔Effect of the invention〕

As can be understood from the above description, according to the VTR of the present invention, the rotational speed of the rotary head during playback is faster than during recording, and moreover, the traces are made to match the recording tracks, so that the playback signal is As a result, the level of the reproduction signal obtained from the rotary head increases, the C/N ratio improves, and as a result, the image quality of the reproduced video image improves.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the VTR of the present invention, FIG. 2 is a diagram for explaining the locus on the magnetic tape during recording, and FIG. 3 is a diagram showing the magnetic tape of the rotary head during playback. 4 is a diagram for explaining the arrangement of the rotary head during reproduction in the embodiment of FIG. 1, and FIG. 5 is a diagram for explaining the reproduction signal in the embodiment of FIG. 1. FIG. 6 is a block diagram showing another configuration example, and FIG. 7 is a frequency spectrum diagram of a reproduced signal used to explain the operation of the conventional technique. (5) is a rotating drum, (7a) and (7b) are rotating heads, (9) is a motor, (10) is a rotation control unit, (11)
) is a signal processing section, (28a) and (28b) are preamplifiers, (29) is a changeover switch, (30) is a demodulation section, (31) is an A/D converter, (34) is a frame memory, ( 36) is a D/A converter, (38) is a timing generator, Sl is a playback signal, S is a video output signal, Tp
is magnetic tape. Agent Hidemori Matsukuma 41! f) Broom Iji'Ji'Ji'Ji Figure 8 Conventional f) Follow the circumference of the Yu 1 signal ∆ Kutwom Figure 1 d4 Temperature tape n locus Figure 2 P3 (13) When reproducing the Bokai tape n locus Figure 3: Rad’s placement for playback! /) Explanation Fig. 4 Re-1 signal f) #Nagabukuwa Fig. 5

Claims (1)

[Scope of Claims] Rotating means for making the rotational speed of the rotary head faster during reproduction than during recording; and displacement means for making the locus of the rotary head during reproduction coincide with the recording track on the magnetic tape. A videotape recorder comprising: