JPS61102885A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To securely correct the distortion on the reproduced plane without using any large scale circuit by providing a delay circuit to delay signals supplied to plural heads for certain length of times respectively for recording when recording and reproducing, to and from the plural tracks, the video signals of 1 field using plural swivel heads. CONSTITUTION:Reproduction is done with the same head as the one used for recording i.e. the signals are reproduced from tracks 6a and 6b by heads 1a and 1b respectively. The reproduction signals thus obtained is inputted to a time base corrector 14 through an FM decoder 11. The signals for the upper half of the plane. Reproduced by the head 1a undergoes a delay circuit of a certain delay time. Ones for the lower half reproduced by the head 1b undergoes a delay line which detects the time base fluctuation at the changeover of head in the middle of the plane and change its own delay time in accordance with the detection result in order to correct the time base fluctuation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording and reproducing device that uses a plurality of rotary heads to record and reproduce one field of video signal by dividing it into a plurality of tracks. This invention relates to a recording and reproducing method for properly connecting video signals appearing on a television screen.

[Conventional technology]

Conventionally, helical scan type magnetic recording/reproducing device (hereinafter referred to as VT)
Particularly in consumer VTRs, a system is adopted in which one field of video signal is recorded on one trunk. When considering downsizing a VTR, assuming that the relative speed between the head and the magnetic tape remains unchanged, that is, the recording and playback characteristics do not change, for example, the number of rotations of the rotating drum on which the head is mounted may be doubled, and the rotation speed may be increased. The diameter of the drum is 1
A method of reducing the size to /2 can be considered. According to this method,
Since one field of video signals is divided into two tracks and recorded, there are two signal joints in one field. If one joint is placed in the vertical retrace period as in the conventional one-field/one-trunk case, the other joint will be at the center of the screen. Therefore, in order to realize this method, it is necessary to properly connect the video signals at the center of the screen, but this is not easy. This will be explained below.

Now, assume that two heads record and reproduce the upper and lower halves of the screen, respectively. At this time, if there is a difference in tape tension between recording and reproduction, time discontinuity occurs at the head switching position, resulting in so-called skew. This will be explained using FIG. 4.

Figure 4 (1)) 2 is a magnetic tape, 3a, 3
b are tracks recorded by heads la and lb, respectively. During playback, when the head 1a comes to the head switching point A, the head 1b moves to the position IB that was recorded at the same time as the position A.
, the signal connection at the center of the screen is well established. This situation is shown in FIG. 4(b). Note that P in the figure represents a screen seam. However, if position B shifts to B1 due to changes in tape tension, the position shown in Figure 4 (c
As shown in 1, the signal between B and B1 is lost.

Moreover, when position B shifts to 82, as shown in FIG. 4(d), B2. The signal between B will be repeatedly reproduced. Note that in FIG. 4 (C1, (d), the amount of skew is exaggerated for the sake of explanation. In an actual VTR, the amount of skew is less than one horizontal period, and when received on a home television receiver, the amount of skew is exaggerated. Due to the internally synchronized AFC circuit, this appears as a curvature in the screen as shown in Fig. 4 (ta).

In any case, if skew occurs, the seam at the center of the screen becomes noticeable, which is visually undesirable.

However, it is extremely difficult to prevent skew from occurring in a helical scan type VTR, and this has hindered the realization of a field division type VTR.

In recent years, as ICs have become more highly integrated and lower priced due to advances in semiconductor technology, VTRs have been equipped with digital time base correctors (this consists of a time base variation detection circuit and a time base variation correction circuit, as described below). It is becoming possible to correct skew and jitter by adding DTBC (denoted as DTBC). For example, the DTB shown in Japanese Patent Application Laid-Open No. 58-124385
In C, the amount of time axis fluctuation (time axis error) of the input video signal is detected based on a predetermined phase relationship that exists between the television video signal of a predetermined method and the local standard clock signal,
Samples the input video signal using a standard clock signal,
This is done based on the deviation between the sample phase and a predetermined phase. In addition, the correction involves dividing the time axis error of the input video signal into a large error component whose unit is a sampling clock cycle and a small error component that is less than or equal to one sampling clock cycle, and adjusting the read timing of the former from the shift register appropriately. The latter precise correction is performed by locking the driving clock signal of the D/A converter from which the corrected output video signal is taken out or the input side A/D converter to the standard synchronization signal. This is done by providing a clock signal with phase modulation according to its time axis error.

However, in such a device, simply recording.

If reproduction is performed, signal loss or duplication will occur due to skew, as explained with reference to FIG. In particular, in the case of omission, it cannot be corrected even by DTBC. A known method for solving this problem will be described below.

FIG. 5 is a diagram explaining the principle of a conventionally known system. As shown in the same figure (al), during recording, the video signals of the upper and lower halves of the screen are compressed in time and recorded on their respective tracks, and during playback, they are expanded in time and restored to their original state. In the same figure (bl shows the track pattern on the magnetic tape 2, the time-axis compressed video signal is recorded in the shaded area E of the trunks 4a and 4b. Also, C2D is the head switching point. Therefore, in order to prevent C and D from intersecting with the shaded area E due to the skew,
By appropriately setting the compression rate during recording, signal loss and duplication can be avoided.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional system has disadvantages in that it requires a large capacity memory of about 1/2 field, and also requires two systems with different clock frequencies, resulting in a large circuit scale.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above.
An object of the present invention is to provide a VTR that can reliably correct distortion on the playback screen (without using a large-scale circuit) in a VTR that uses a head to record one field of signals by dividing it into N tracks. The purpose is

[Means for solving problems]

The VTR according to the present invention uses a plurality of rotating heads to
When the video signal of the field is divided into a plurality of tracks and recorded and reproduced, a delay device is provided to delay each signal reproduced by the plurality of heads by a predetermined time.

(Operation) In the present invention, the signals reproduced by the plurality of heads are each delayed by a predetermined time, and the reproduced signal without any omission at the joint inside the screen is input to the DTBC,
To surely correct distortion on a playback screen.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a recording system of a VTR according to an embodiment of the present invention.

The schematic configuration of the signal processing of the reproduction system is shown, and in this embodiment, the number of heads is two. These recording amplifiers 8a are provided correspondingly to the recording amplifiers 8a.

Outputs s and t of 8b are supplied to heads la and lb, respectively. Further, 9a and 9b are playback amplifiers that amplify the playback signals u and v of the HDDs la and lb, respectively, 15a is a delay device that delays the output of the playback amplifier 9b by a predetermined time T, and 10 is the output of the playback amplifier 9a and a delay device. Input the output of 15a,
The switching circuit 1) which outputs one of the two human powers in synchronization with the rotation of the rotary drum 5 is an FM demodulator which demodulates the output of the switching circuit 10 into FM. Reference numeral 14 denotes a time axis fluctuation detection circuit 12 that detects fluctuations in the time axis of each reproduced signal, and a time axis fluctuation correction circuit 13 that corrects the above-mentioned time axis fluctuations according to the detection result.
This is a time axis corrector that outputs a corrected video signal W.
It is publicly known as shown in Publication No. 5 and the like.

FIG. 2(a) is a diagram showing the head arrangement of the VTR according to this embodiment.
Mounted at an angle of °. Also, this rotating drum 5
rotates once in one field period.

2) is a diagram for explaining the tape pattern recorded by the VTR of this embodiment, and in the figure, 6a and 6b are trunks recorded by heads la and lb, respectively. Video signals for the upper half and lower half of the screen are recorded in the trunks 5a and 5b, respectively. Also, C, D,
The positions shown in E correspond to the positions with the same symbols in FIG.

Here, positions C and D indicate the positions of heads la and lb at the time when the switching circuit shown in FIG. 1 (O1+) performs the switching operation. The E position will be described later.

Next, the operation will be explained.

The input video signal r is FM modulated by the FM modulator 7, and sent to the head l as signals s and t via the recording amplifiers 13a and 3b.
a, lb. And these noherad Ia, l
The video signals supplied to tracks 6a and 6b are respectively
recorded in

Next, the operation during playback will be explained. Reproduction is performed using the same head used for recording. That is, head la
, lb to reproduce signals from tracks 6a and 5b, respectively. The case of reproducing the field division point portion will be explained using FIG. 2 (bl).

When the head 1a plays back the section C on the trunk 6a, the head 1b is at the section D on the trunk 6b.

At this point, the switching circuit 10 shown in FIG.
The signal at position E in Figure (bl) is output. In other words, this position E indicates the position where the signal recorded at point D is a time T earlier than the signal recorded at point D. Here, if the delay time T is set to be greater than the maximum amount of time axis variation expected at the time of head switching, the signal will not be dropped when the head is switched at the center of the screen.

The reproduced signal obtained in this way is inputted to the inter-interval 1 corrector 14 through the FM jiffi unit 1), and the signal of the upper half of the screen reproduced by the head la passes through a delay circuit of a predetermined time and is reproduced by the head 1b. The signal in the lower half of the screen can be corrected by detecting the amount of time axis variation when switching heads at the center of the screen, and passing it through a delay line whose delay time changes according to the detection result. can.

In this embodiment, the reproduction signal from the head that reproduces the lower half of the screen is delayed during reproduction.
It is possible to eliminate the loss of the reproduced signal at the joint in the center of the screen. Therefore, the DTBC which inputs the reproduced signal
With this method, it is possible to reliably correct time axis fluctuations, and it is possible to prevent skew from occurring at the seams. Additionally, this embodiment eliminates the need for large-capacity memory as in the conventional case.
The device can be made inexpensive.

In the above embodiment, the head amplifier output is delayed, but as shown in FIG. 3, the FM modulator 1)a
, llb may be provided, and one output signal may be delayed by the delay device 15b and then switched to be input to the time axis corrector 14, and the same effect as in the above embodiment can be obtained.

Also, the number of heads is not limited to two (in general, in a system where one field of video signal is divided into N trunks and recorded by N heads (N is an integer greater than or equal to 2), n (n-”21...

If the signal reproduced by the (N)-th head is delayed by a predetermined time from the signal reproduced by the (n-1)-th head, it is possible to prevent signal loss within the screen, as described above. Therefore, it is possible to prevent skew from occurring at the joint portion.

Furthermore, by making the azimuths of adjacent heads different, high-density recording without guard bands is also possible.

〔Effect of the invention〕

As described above, according to the present invention, the signal reproduced by each head during recording is delayed by a predetermined time for each head, thereby preventing signal loss when switching heads at the joint inside the screen during reproduction. This has the effect that distortion on the playback screen can be reliably corrected using a simple and inexpensive device.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a recording system and a reproducing system of a VTR according to an embodiment of the present invention, and FIG. 2 is a diagram of a VT according to an embodiment of the present invention.
FIG. 3 is a schematic configuration diagram of a VTR playback system according to another embodiment of the present invention, and FIG. 4 is a diagram for explaining the influence of time axis fluctuations on a VTR. 5 are diagrams for explaining a method for correcting time axis fluctuations in a conventional VTR. 1 a, l b-head, 2...tape, 3a,
3b. 4a, 4b, 6a, 6b..., video signal track, 5.
... Rotating drum, 12 ... Time axis fluctuation detection circuit, 13
...Time base fluctuation correction circuit, 15a, 1'5b...Delay device. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) N heads installed on a rotating drum at intervals of 360°/N (N is an integer of 2 or more) that record one field of video signal by dividing it into N tracks; A time axis variation detection circuit receives the reproduction signal of the head and detects the variation in the time axis of each reproduction signal at the seam of the screen, and a time axis variation correction circuit corrects the above-mentioned time axis variation according to the detection result. In the helical scan magnetic recording and reproducing device, the signal reproduced by the nth (n=2, . . . , N) head is delayed by a predetermined time from the signal reproduced by the (n-1)th head. A magnetic recording and reproducing device characterized by being equipped with a delay device. (2) The magnetic recording/reproducing apparatus according to claim 1, wherein the number N of heads is two.