JP2707611B2 - Rotating head type recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary head type recording apparatus, and more particularly to a rotary one head type rotary head type recording apparatus.

[Conventional technology]

Currently widely used, for example, for home VTR (hereinafter,
A normal VTR) has a magnetic tape wound around a rotating angle of about 180 ° around the rotating drum, and is rotated about 180 °
A pair of rotary heads are attached while maintaining the angular spacing of. The pair of rotary heads records and reproduces video signals of two fields as two tracks by one rotation of the rotary drum.

With respect to such a normal VTR, for example, as shown in FIG. 7, the winding angle is increased to about 300 °, and one rotating head 44 records a video signal of one field by one rotation of the rotating drum 40. There is a rotating one-head type VTR configured to reproduce.

In the rotating one-head type VTR as described above,
Since there is one rotating head 44, there is a feature that angle division is not required as compared with a normal VTR. Also, normal VT
In the case of R, the video signal for one field is recorded by 1/2 rotation of the rotary drum 40, so the rotation frequency is 30 Hz. In the case of the one-head system, the video signal for one field is generated by one rotation of the rotary drum 40. Is recorded, the rotation frequency is doubled to 60 Hz. Therefore, since the relative speed between the rotary head 44 and the magnetic tape is increased, the CN ratio can be made advantageous. If the CN ratio is constant, the rotary drum 40 can be downsized.

[Problems to be solved by the invention]

However, as described above, the rotating one-head type VT
In the case of R, since the video signal of one field or one frame is recorded by compressing the time axis, at the time of reproduction, the timing of the reproduced horizontal synchronizing signal is extracted, and based on this timing, the clock for expanding the time axis by PLL is used. A pulse is formed.

In the above process, during the period in which the playback video signal is interrupted, the PLL runs by itself, so that when the playback video signal is obtained, the phase of the PLL output and the phase of the playback horizontal synchronization signal do not match. There is a problem that the pull-in time of the PLL for the reproduced video signal is prolonged. Further, while the PLL cannot lock to the reproduced horizontal synchronizing signal, the reproduced video signal cannot be synchronized, so that a horizontal synchronizing flow occurs.

Accordingly, an object of the present invention is to provide a rotary head type recording apparatus in which a PLL can be locked in a short time with respect to a reproduced horizontal synchronizing signal in a reproduced video signal.

[Means for solving the problem]

According to the present invention, in a rotary head type recording apparatus that includes one rotary head that makes one rotation in a period of one field or one frame, and that records a video signal that is time-axis compressed by the rotary head, the time-axis compression ratio is m / n, and the wrap angle is (m / n) x 360 degrees, and a video signal for one field or one frame, which is compressed at a time axis compression ratio, is recorded on the wound magnetic tape. In the axial compression ratio, m and n are relatively prime, so that m is a divisor of the number of horizontal scanning periods in one frame, and one field or one field corresponding to one rotation of the rotary head.
The number of horizontal scanning periods per frame period is set to be an integer or (integer + 0.5).

[Action]

When recording a VTR in the rotating one head system, the compression ratio is selected such that the number of horizontal scanning periods per one rotating cycle of the rotating head is an integer or (integer + 0.5).
On the basis of this compression ratio, the video signal is transmitted in one field or one field.
The time axis is compressed for each frame, and the compressed video signal is recorded. At the time of reproduction, the PLL is locked to the reproduced horizontal synchronizing signal separated from the compressed reproduced video signal, and a clock for time axis expansion is formed.

In a rotating one-head type VTR, there is a so-called idle running period in which the rotating head is not in contact with the magnetic tape in one rotating cycle of the rotating head. During playback, during this idling period,
Since no reproduced video signal is output, a reproduced horizontal synchronizing signal cannot be obtained, and the self-running period of the PLL occurs.

When the number of horizontal scanning periods per one rotation cycle of the rotary head is an integer, the PLL runs by itself while maintaining phase synchronization even in the free running period, and enters the video signal section of the next field or frame. Quickly lock to the playback horizontal sync signal.

When the number of horizontal scanning periods is (integer + 0.5),
In the integer part, the PLL runs on its own while maintaining phase synchronization,
When the detecting means detects the head of the next reproduced video signal, the phase of the PLL is switched, so that when the video signal section of the next field or frame is entered, the phase is immediately locked to the reproduced horizontal synchronization signal.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, as shown in FIGS. 1 to 6, the present invention is applied to a rotary one-head type VTR. The description will be made in the following order.

(A) Recording system of VTR (B) Time axis compression of video signal during recording (C) Reproduction system of VTR (D) Locking of PLL during reproduction (A) Recording system of VTR Fig. 1 2 shows a block diagram of a recording system in the VTR.

In FIG. 1, a video signal supplied from a terminal 1 is supplied to a low-pass filter 2 and a sync separation circuit 3, respectively.

The output signal of the low-pass filter 2 is supplied to the A / D conversion circuit 4. On the other hand, in the sync separation circuit 3, a horizontal sync signal is extracted from the video signal, and the separated horizontal sync signal is
Supplied to L5. In the PLL 5, a clock pulse synchronized with the horizontal synchronization signal is formed, and this clock pulse is supplied to the timing generator 6.

In the timing generator 6, the clock pulse CK1 of the first frequency is generated based on the supplied clock pulse.
[Hereinafter abbreviated as a first clock pulse] and the first clock pulse
Clock pulse CK2 of a second frequency higher than the frequency of
[Hereinafter, abbreviated as a second clock pulse] are respectively formed. Then, the first clock pulse CK1 is supplied to the A / D conversion circuit 4 and the memory 7, and the second clock pulse CK2 is supplied to the memory 7 and the D / A conversion circuit 8.

In the A / D conversion circuit 4, the supplied video signal is digitized in synchronization with the above-mentioned first clock pulse CK1,
This digital data is supplied to the memory 7. Memory 7
Then, digital data is written in synchronization with the above-mentioned first clock pulse CK1. And the second clock pulse
Digital data is read out in synchronization with CK2 and supplied to the D / A conversion circuit 8. The frequency f2 of the second clock pulse CK2 is set higher than the frequency f1 of the first clock pulse, and the video signal is time-axis-compressed at a ratio of the frequencies f1 and f2. This compression ratio is (m /
n).

In the D / A conversion circuit 8, the digital data read from the memory 7 is converted into an analog video signal in synchronization with the second clock pulse CK2. FIG. 3 shows a state where the input video signal is time-axis-compressed for each field at a compression ratio (m / n) to be described later.
Indicates a so-called idle running period in which the rotating head 10 does not contact the magnetic tape 11. The output signal of the D / A conversion circuit 8 is supplied to the low-pass filter 12, and the output signal of the low-pass filter 12 is supplied to the FM modulation circuit 13. The video signal from the FM modulation circuit 13 is supplied to the rotary head 10 via the amplifier 14, and the video signal for one field whose time axis is compressed is recorded on the magnetic tape 11 by the rotary head 10.

(B) Time-axis compression of video signal at the time of recording The ratio of the frequency of the first clock pulse CK1 to the frequency of the second clock pulse CK2 defines the compression ratio of the video signal and the winding angle of the magnetic tape 11 around the rotating drum 15. ing.

(B-1) Compression Ratio As described above, the frequency ratio of the first clock pulse CK1 and the second clock pulse CK2 (f1 / f2, where f1 <f2 corresponds to the compression ratio (m / n). Here, m and n are both integers and m <n, and m / n is an irreducible fraction.

When m in the above-mentioned compression ratio (m / n) is a combination of prime factors of the number of scanning lines of the television, the time required for pulling in the PLL 5 during reproduction can be reduced.

For example, in the case of the NTSC system, since the number of scanning lines per frame is 525, it is factored into 525 = 5.55.7 / 3. When the video signal of one frame is compressed on the time axis by the above-described compression ratio (m / n), the rotation head 10
The number of horizontal scanning periods (hereinafter abbreviated as H) included in the rotation period (one frame period) is obtained by multiplying the number of scanning lines per frame by the reciprocal of the compression ratio. That is, FIG. 5 shows a state of H which is compressed on the time axis in one rotation cycle of the rotary head 10. This one field period is composed of video signals from 1H to 262.5H, and an idle running period 9 after 262.5H, that is, a self-running period of PLL5. Reference numeral 16 denotes H defined by the timing generated from the PLL 5 in the idle running period 9.

Here, m is selected as a combination of prime factors (5, 7, 3),
If n is an even number, the phase of the compressed H can be matched within one frame period as shown in FIG. 6C.
If n is an odd number, the phase of the compressed H has a phase jump of 0.5H within one frame period as shown in FIG. 6A.

To make the compression ratio common in both NTSC and PAL directions,
The number of scanning lines of the PAL system is 625, and (625 = 5.5.5.
Since the prime factorization is performed in 5), m = 5 or m = 25
Must be selected.

(B-2) Winding Angle θ The winding angle θ is expressed by the following equation.

In the VTR of the rotating one head system, the above-mentioned condition of the winding angle θ is as follows. To be Becomes

Here, when the respective compression ratios when m = 25, n = 33 or 34 are set and the number of Hs formed in one field period (NTSC system) are obtained, the following is obtained.

As is clear from the above calculation results, when m is a combination of the prime factors of the scanning lines and n is an odd number, a phase jump of 0.5H is formed in one field period (one rotation period of the rotary head 10). On the other hand, if m is a combination of the prime factors of the scanning lines and n is an even number, the number of H becomes an integer in one field period.

(C) Reproduction system of VTR In the configuration of Fig. 2, a rotating head with a rotating frequency of 60Hz
The reproduced video signal reproduced and FM-modulated by 10 is amplified by an amplifier 21 and then FM-demodulated by an FM demodulation circuit 22. The output signal of the FM demodulation circuit 22 is supplied to a low-pass filter 23 and a synchronization separation circuit 24. As shown in FIG.
The reproduced video signal is formed every one field period including the idle running period 9, and an overlap portion 18 is provided at the front end of the reproduced video signal for each field. The output signal of the low-pass filter 23 is supplied to the A / D conversion circuit 25.

On the other hand, in the above-mentioned sync separation circuit 24, a playback horizontal synchronization signal in the playback video signal is extracted and supplied to the PLL 27.

The PLL 27 locks to the reproduced horizontal synchronizing signal and forms a clock pulse synchronized with the timing of the reproduced horizontal synchronizing signal.
Supplied to

The timing generator 28 generates a first clock pulse based on the clock pulse synchronized with the reproduced horizontal synchronization signal.
CK1 and a second clock pulse CK2 are formed. And
The second clock pulse CK2 is supplied to the A / D conversion circuit 25 and the memory 26, and the first clock pulse CK1 is supplied to the memory 26 and the D / A conversion circuit 29, respectively.

In the A / D conversion circuit 25, the supplied reproduced video signal is
The digital data is digitized in synchronization with the second clock pulse CK2, and the digital data is supplied to the memory 26. In the memory 26, digital data is written in synchronization with the above-mentioned second clock pulse CK2. Then, the digital data is read out in synchronization with the first clock pulse CK1, and the output signal of the memory 26 is supplied to the D / A conversion circuit 29. The frequency f1 of the first clock pulse CK1 is equal to the second clock pulse CK2
Since the frequency is set lower than the frequency f2, the reproduced video signal is expanded on the time axis. In the D / A conversion circuit 29, the digital data read from the memory 26 is converted into an analog reproduced video signal in synchronization with the first clock pulse CK1, and is supplied to the low-pass filter 30.
An output signal of the low-pass filter 30 is output to an output terminal 31.

(D) Regarding PLL lock at the time of reproduction The reciprocal of the compression ratio (m / n) of the video signal defined by the respective frequencies f1 and f2 of the first and second clock pulses CK1 and CK2, that is, n / m
Is the time axis expansion ratio of the reproduced video signal.

When (m / n = 25/33) in the above-described recording system, the number of Hs included in one rotation cycle (one field period) of the rotating drum 15 is 346.5, which is shown in FIG. 6A. Thus, between the first H of the playback video signal section next to the idle running period 9,
A 0.5H phase jump occurs. In this case, the PLL 27 is controlled by the control signal shown in FIG. 6B formed by detecting means for detecting the rotational phase of the rotary head 10, and the reproduced horizontal synchronizing signal generated in the next reproduced video signal section. PLL27 is locked immediately.

When (m / n = 25/34), the number of Hs included in one rotation cycle (one field period) is 357,
As shown in FIG. 6C, the phase of H16 during the idle running period 9 is
It becomes the same as the phase of H in the next reproduced video signal section. Therefore, the PLL 27 is quickly locked to the reproduced horizontal synchronizing signal generated in the next reproduced video signal section.

In this embodiment, an example in which a video signal is recorded for each field is described. However, the present invention is not limited to this. When recording a video signal of one frame in one rotation cycle of the rotating drum 10, Can be similarly applied. Also at this time, the phase skip of 0.5H due to the even and odd numbers of n in the compression ratio is eliminated. Further, the present invention can be similarly applied to recording of a composite color video signal or a component color video signal.

〔The invention's effect〕

According to the present invention, by selecting the ratio of the time axis compression so that the number of 1Hs per field or one frame period becomes an integer or (integer + 0.5), the pull-in time of the PLL at the time of reproduction can be greatly reduced. Can be shortened. For this reason,
This has the effect of preventing the occurrence of horizontal synchronization flow.

[Brief description of the drawings]

FIG. 1 is a block diagram of a VTR recording system according to an embodiment of the present invention, FIG. 2 is a block diagram of a VTR reproducing system according to an embodiment of the present invention, and FIG. , FIG. 4 is a schematic diagram used for describing a reproduced video signal, FIG. 5 is a schematic diagram showing an arrangement of compressed horizontal scanning periods, and FIG. 6 is a one-field period reproduced respectively. FIG. 7 is a schematic diagram showing the arrangement of a per-reproduction video signal in a horizontal scanning period, and FIG. 7 is a schematic diagram showing the arrangement of a rotary head that can be used in the present invention. Description of main symbols in the drawings 5, 27: PLL, 10, 44: rotating head, H: horizontal scanning period, m / n: compression ratio.

Claims (1)

(57) [Claims] 1. One frame or one frame period.
A rotary head type recording apparatus comprising one rotating rotary head for recording a video signal compressed on the time axis by the rotary head, wherein the ratio of the time axis compression is m / n and the winding angle is (m / n) X 360 degrees, a video signal for one field or one frame compressed at the above-mentioned time axis compression ratio is recorded on the wound magnetic tape. In the above time axis compression ratio, m and n are , Relatively prime, m
Is a divisor of the number of horizontal scanning periods in one frame, and the number of the horizontal scanning periods per field or one frame period corresponding to one rotation of the rotary head is an integer or (integer + 0.5) A rotary head type recording apparatus.