JPS6262402A - Recording and reproducing device for video signal - Google Patents

Abstract

PURPOSE:To demodulate an original video signal correctly by extracting a frequency component corresponding to the specified level of a video signal having two signals by two heads and providing a means to correct so as to always keep the phase difference of the extracted two signal at 90 deg.. CONSTITUTION:A signal reproduced by a head HB or HD is supplied to a high-pass filter 35 through a pre-amplifier 34 and a reproducing signal FF2' that is a liminance component is obtained, and the signal FF2' is supplied to an astable multivibrator 33 through a limiter 36 and a variable delay circuit 37. At the astable multivibrator 33, an FM signal SF' is formed from a signal FF1' and the FF2', and the FM signal SF' is supplied to an FM demodulation circuit 38, being FM-demodulated and the demodulated output is changed to an original luminance signal Y through a de-emphasis circuit 39, being derived to an output terminal 40. At such a case, provided that the phase difference between the signals FF1' and FF2' in a recording time, that is, the phase difference of 90 deg., is maintained correctly, a correct FM signal SF is restored without distortion from the astable multivibrator 33.

Description

[Detailed description of the invention] The invention will be explained in the following order.

A. Field of industrial application B. Overview of the invention C. Prior art D. Problem to be solved by the invention E. Means for solving the problem (Fig. 1) F. Effect G. Example G1 Description of the first example (Fig. 1, Fig. 2, Fig. 3, Fig. 7) G2 Explanation of the second embodiment (Fig. 4 to Fig. 6) Effect A of the invention The present invention relates to a device that performs FM modulation on a signal, records it, and reproduces the same.

B. Summary of the Invention This invention divides a frequency-modulated signal into 1/2 and divides it into two signals with a 90° phase difference from each other, which are simultaneously recorded as two tracks using two heads and reproduced. At this time, the two heads are installed so that even if there is an error in the position of each recording/reproducing device, the two reproduced signals always have a 90° phase difference. This makes it possible to correctly reproduce the original FM modulated signal and, in turn, to correctly demodulate the original video signal.

C. Conventional technology Various technologies have been proposed for recording wideband video signals such as high-definition television signals, but when using recording methods that have been commonly used up until now, it is difficult to record this wideband video signal. There was not enough bandwidth for recording, and the relative speed of the rotating head had to be increased. Therefore, measures such as increasing the diameter of the rotary head drum and increasing the rotational speed of the rotary head were required.

However, this method has drawbacks such as an increase in the size of the apparatus due to the increased drum diameter and an increase in head wear and tear.

Therefore, the video signal is FM-modulated, and the FM-modulated signal SF (Fig. 7A) is divided into a signal FF1 (Fig. 7B) by its rising edge, and a signal FF2 (Fig. 7B) which is frequency-divided by the falling edge of the signal -3F. C) in the same figure, and recorded these signals FF1 and FF2 simultaneously as one track each using a solid head (see Utility Model Application Publication No. 58-77963). In this way, Then, the signal recorded by one head has a frequency that is 1/2 that of the signal SF, and can be sufficiently recorded and reproduced by a device having the same head drum diameter and head rotation speed as the conventional one.

When performing such recording, if the recording track pattern on the tape is to be the same as the conventional one, two ([[
A total of 4 rotating heads HA, each lil.

HB, HC, and HD are installed, and heads HA and HB and heads HC and HD have the same azimuth angle, but heads HA and HB and heads HC and HD have different azimuth angles. On the other hand, heads HA and HB and heads HC and HD are shifted in the height direction as shown in FIG. 8B, and a track pattern as shown in FIG. 9 is formed on the tape.

That is, during the first 1/2 rotation period of one rotation of the drum, the aforementioned two divided trunks are formed as trunks T1 and T3 by helads HA and HB of the same azimuth.
Assuming that the signals FFI and FF2 are recorded, during the remaining 1/2 rotation period in the latter half, the heads HC and HD record the track T? , T4 as signals FFz and FF2
is recorded. In the first half of the next rotation, heads HA and H
Track 75. by B. Signal FF Yu and F as T7
F2 is recorded, and the head HC is recorded during the second half rotation period.
and signal FF1 as trunk TG, Ta by HD and
and FF2 are recorded. This operation is repeated thereafter. In this case, the distance in the height direction between the heads HA and HB and the distance in the height direction between the heads HC and HD are the two tracks formed by the heads HA and HB, as is clear from the above track formation. The values are selected such that a track is formed by the head HC during the rotation, and a track by the head HD is formed between the track formed by the head HB and the track formed by the head HA in the next revolution (Japanese Patent Application Laid-Open No. (See No. 161108, 1982).

D. Problems to be Solved by the Invention As described above, it is possible to record and reproduce broadband video signals without changing the drum diameter or the rotational speed of the rotary head. H.A.
and recording signals FFx and F by HB or heads HC and HD
F2 is a signal with a phase difference of 90°, and during playback,
The original signal SF is reproduced from these two signals with a 90° phase difference.

In this case, when recording and playing back on the same VTR, assuming that there is no discrepancy in the mounting positions of heads HA and HB or heads HC and HD due to aging, the reproduced signals FF□ and FF2 has exactly a phase difference of 90°.

Therefore, a wideband video signal can be correctly demodulated.

However, in reality, it is often the case that one plays back what was recorded on another VTR. In this case, the heads HA and HB, and heads HC and HD should be installed without errors in their positions, and all VT
If R is exactly the same, no problem will arise, but in practice it is impossible to place exactly the same mountings in exactly the same position. For this reason, the reproduced signals FF1 and FF2 are rarely reproduced correctly with a phase difference of 90°, and a slight phase shift occurs. Since this deviation corresponds to a frequency deviation of the FM modulation signal, the signal SF may not be reproduced correctly, and therefore the video signal may not be demodulated correctly.

E. Means for Solving the Problems In this invention, two signals obtained by dividing a frequency-modulated video signal into signals whose phases differ by, for example, 90" and whose frequency is 1/2 of the original signal, are divided into two signals. In a device that records and plays almost simultaneously using two heads, during playback, a frequency portion corresponding to a specific level of two video signals is extracted from two heads, and the phase difference between the two extracted signals is 90 degrees. Provide a means for correcting it so that it always remains the same.

F Effect Even if there are errors in the arrangement of the two heads for each VTR,
Since the reproduced outputs of these two heads are always corrected to have a phase difference of 90°, the original video signal can be demodulated almost accurately by demodulating the FM signal returned from these two signals.

G Embodiment G1 Description of the First Embodiment FIG. 1 is a block diagram of an example of the apparatus of this invention, and this example is an example in which the rotary head apparatus shown in FIG. 8 is used.

In the figure, (11) is an input terminal for the luminance signal Y, and the signal through this is supplied to the mix circuit (I2).

On the other hand, a reference level signal REF is supplied to the mix circuit (12) through a terminal (13) during several horizontal intervals after the vertical synchronizing signal VD during the vertical blanking period.

This reference level is the black level of the luminance signal
%, when the white health is set to APL 100%, it is set to the level of APL 50%, which is exactly in the middle. Therefore, as shown in FIG. 2A, from this mix circuit (12), a reference level signal REF is superimposed in several horizontal sections after the vertical synchronizing pulse VD within the vertical blanking period (excluding the horizontal synchronizing pulse part). A signal YM in a state where the

This signal YM is supplied to an FM modulation circuit (15) through a pre-emphasis circuit (14) and subjected to FM modulation. The signal SF (see FIG. 7C) from this FM modulation circuit (15) is passed through a flip-flop (17) via a delay circuit (16).
), from which the signal SF whose state is inverted at the rising edge of the signal SF is divided by 1/2 is the signal FF.
1 (see FIG. 7C) is iMed. This signal FFt is then supplied to an adder circuit (18) and added to a balanced modulation color signal C having a carrier frequency of 3 MIIz which occupies a lower band than this signal FFI from a terminal (19).

Further, a polarity inverted signal n of the signal SF is obtained from the FM modulation circuit (15), and this signal is passed through the flip-flop (20
), which inverts its state at the rising edge of the signal Ω and therefore at the rising edge of the signal SF.
2 (see Figure 7C) is obtained, and this is the delay circuit (2
1) to the adder circuit (22), and the terminal (23
) is added to the balanced modulated color signal C from ).

The delay circuits (16) and (21) are for the engine timing of the divided signals FF1 and FF2.

Signals from the adder circuits (18) and (22) are sent via the recording amplifiers (24) and (25), respectively, to the recording side terminals REC of the recording/reproduction changeover switches (26) and (27) to the head switching circuit (28). ). A head switching signal RFSW is supplied to this switch circuit (28) through a terminal (29), and when the heads HA and HB scan the tape, the terminal A side is used, and when the heads HC and KD scan the tape, the head switching signal RFSW is supplied to the terminal A side. They can each be switched to the terminal B side.

Therefore, as shown in FIG. 9, the rotating head HA,
By HB two trunks Tyu and T3. T5, T7, .
T6 and T8゜... are formed in sequence to generate signals FFL and F.
F2 is added to color signal C and recorded.

In this way a wideband video signal is recorded.

That is, a wideband video signal as shown in FIG. 3A is recorded as a signal in which the luminance signal is band-compressed for one head as shown in FIG. 3B.

As mentioned above, the color signal is recorded as a balanced modulation carrier of 3M1 (z), but since this causes a lot of crosstalk on the low frequency side, PI (phase inversion) processing and PS (phase Shift) processing is designed to remove crosstalk during playback.

The signals recorded in this way are reproduced as follows.

Even during this reproduction, the switch circuit (28)
The FSW switches to the terminal A side during the 1/2 rotation period when the heads HA and HB scan the tape, and to the terminal B side during the 1/2 rotation period when the heads HC and HD scan the tape.

The signal reproduced by the head HA or HC is supplied to the bypass filter (31) through the preamplifier (30), from which a reproduced signal FF1' which is a luminance signal component is obtained, and this is passed through the limiter (32) to the bypass filter (31). The staple is supplied to the multi-byte break (33).

On the other hand, the signal reproduced by head HB or HD is supplied to a bypass filter (35) through a preamplifier (34) to obtain a reproduced signal FF2' which is a luminance component, and this signal FF2' is sent to a limiter (36) and Astable multi-by-break (
33). In this astable multi-by-break (33), the signals FF1' and FF
2', an FM signal SF' is formed, and this FM signal SF
' is supplied to the FM demodulation circuit (38) and FM demodulated,
The demodulated output is converted into the original luminance signal Y through a de-emphasis circuit (39) and is output to an output terminal (40).

In this case, if the signals FF1' and FF2' supplied to the astable multi-vibrator (33) maintain a correct phase difference during recording, that is, a 90° phase difference, then the signals FF1' and FF2' supplied to the astable multi-vibrator (33) can be The FM signal SF is correctly restored without distortion.

The variable delay circuit (37) is for maintaining the 90° phase difference. That is, the limiter (32)
The signal FF1' from the variable delay circuit (37) and the signal FF2' from the variable delay circuit (37) are supplied to the gate circuit (41). This gate circuit (41) is supplied with a gate signal GT (FIG. 2B) that becomes high level during a specific period within the vertical blanking period on which the reference level signal REF is superimposed. Therefore, the reference level (
FM carrier corresponding to APL50%) is signal FF1'
and that taken out from FF2' are obtained. Among them, for example, the FM extracted from the signal FF1'
The carrier is phase-delayed by 90° by the 90° phase shift circuit (43) and supplied to the comparison circuit (44), and the signal FF
The FM carrier taken out from 2' is directly supplied to a comparison circuit (44), and the phases of the two are compared. The comparison error output is then supplied to a variable delay circuit (37) to control the amount of delay.

Through this control, the signals FF1' and FF2' are
The carrier portion corresponding to the reference level (APL50%) is made to have a correct phase difference of 90°.

That is, heads HA and HB or heads HC and HD
Even if there is a placement error in the positional relationship with the VTR, it can be almost ignored, and compatibility between the VTRs can be maintained.

Note that this reference level is the level value at the center of the luminance signal in this example, so even if the phases of both signals are shifted on the black level side or color peak level side, the shift is small, and therefore the signal Almost the original luminance signal Y can be correctly reproduced from SF'.

Note that this placement error between the heads HA and HB or between the heads HC and HD also appears for the color signal C, but the comparison circuit (
This color signal C can also be corrected by the output of 44).

That is, the signals passed through the preamplifiers (30) and (34) are passed through the low-pass filters (45) and (46), respectively.
From this, a balanced modulation carrier of the color signal C is obtained, and this is supplied to the chroma processors (47) and (4), respectively, where PI or PS processing is performed to cancel crosstalk.

Then, the output of the processor (47) is sent to the synthesis circuit (50).
The output of the processor (48) is connected to a variable delay circuit (49).
are respectively supplied to the synthesis circuit (50) via the composing circuit (50), and the original balanced modulated color signal is taken out as is as the synthesized output, but the delay amount of the variable delay circuit (49) is the output of the comparator circuit (44). This reduces the adverse effects of head mounting errors for each VTR.

With this playback, the third
The luminance signal whose band is compressed to 172 as shown in Figure B is expanded as shown in Figure C, and the luminance signal occupying the band as shown in Figure B and the color signal occupying the band as shown in Figure E are reproduced. .

G2 Description of Second Embodiment In the above example, a reference level signal is inserted into the vertical blanking section in order to correct head placement deviation. The correction may be made based on the carrier of the portion.

Further, a MUSE system signal has been proposed as a wideband television signal, but this MtlSE system television signal is a signal as shown in FIG. 4A. As is clear from the figure, an upward horizontal synchronizing signal HD is inserted into this signal, and its peak level is the center value of this television signal. Therefore, in the case of this MUSE system signal, the FM carrier of this horizontal synchronization signal can be used as a reference for correction.

FIG. 5 is a system diagram for recording and reproducing signals of this MUSE system, in which the MtlSE signal through the input terminal (51) is passed through the pre-emphasis circuit (52) to the FM modulation circuit (
53) to form an FM modulated signal SFM. The FM modulation signal SFM and its polarity inverted signal SFM are respectively supplied to flip-flops (54) and (55) and frequency-divided by 1/2, so that the band is compressed to 1/2 and the phases differ by 90 degrees from each other. Signal 5FF1 and 5FF
These signals 5FFL and 5FF2 are supplied to the head changeover switch circuit via recording amplifiers (56) and (57), recording and playback changeover switches (5th) and (59), respectively, H.C.

The HD records data sequentially as two recording tracks in the same manner as described above.

In this case, a broadband signal Y+C as shown in FIG. 6A is recorded as a compressed signal Y'+C' as shown in FIG. 6B.

Next, the signals recorded in this way are transmitted to heads HA and HB.
The signals from the two tracks are sequentially reproduced by the heads HC and HD, and the signals from the two tracks are each sent to a preamplifier (6
0) and (61) to limiters (62) and (63).
), the output 5FFi' of the limiter (62) is supplied to the astable multivibrator (66) via a delay circuit (64) for fine adjustment, and the output 5FF2' of the limiter (63) is a variable delay circuit for correction. It is supplied to the Astable multi-by break (60) via the circuit (65).The Astable multi-by break (60)
), a signal SFM' expanded to an FM signal in the original band is obtained, which is FM demodulated by an FM demodulation circuit (67), and the demodulated output is led out to the output terminal of the MtlSE signal via, for example, a de-emphasis circuit. Ru.

In this example, the signals SFF' and 5FF2' from the delay circuit (64) and the variable delay circuit (65) are supplied to the gate circuit (68), and the signals are supplied to the terminal (69).
The gate signal GTS (Fig. 4B), which becomes high level during the period of the upward horizontal synchronizing pulse, is connected to this gate circuit (6
8), from which signals 5FF1' and 5FF
7 horizontal synchronizing pulse sections are obtained, one of which is passed through a 90° phase shift circuit (70) to a comparator circuit (70).
1), the other is supplied as is to the comparison circuit (71),
The output of this comparison circuit (71) controls the delay amount of the variable delay circuit (65), and the signals 5FF1' and SF
The carrier corresponding to the F# synchronization signal level is correctly 90.
It is controlled to have a phase difference of °.

In this example as well, since the level of the horizontal synchronizing signal HD is the median value of the signal, the signal SFM can be reproduced almost correctly, as in the case of the reference signal REF described above.

With the above recording and reproduction, in the case of the example shown in Fig. 5, the 6th
A reproduced signal with a baseband bandwidth as shown in FIG. C is obtained.

In the case of this MjISE method, the audio signal is a PCM signal, but if this PCM audio signal is recorded as it is, it will be difficult to demodulate it due to the jitter of the device.

Therefore, the audio signal is recorded in a four-carrier format as shown in FIG. 6B in the same manner as when the audio signal is recorded as an FM signal on the lower frequency side of the video signal in a home VTR.

Effects of the invention H According to this invention, the band of the FM signal is compressed to 1/2.
When splitting signals into signals, recording and reproducing the two signals simultaneously using two heads, even if there is an error in the mounting position of the two heads for each device, it is necessary to correct it. Therefore, the original FM signal can always be reproduced well.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an example of this invention device, FIGS. 2 and 3 are diagrams for explaining the same, FIG. 4 is a diagram showing an example of a high-definition television signal, and FIG. 5 is a block diagram of an example of this invention device. A block diagram of another example, FIG. 6 is a diagram for explaining the same, FIG. 7 is a diagram for explaining the method of dividing the FM signal into two, and FIG.
The figure is a diagram for explaining an example of a rotary head device, and FIG. 9 is a diagram showing an example of a recording track pattern by the rotary head device. (15) is an FM modulation circuit, (17) and (20) are flip-flops for frequency division, (37) is a variable delay circuit, (3
8) is an FM demodulation circuit, and (44) is a comparison circuit for comparing the phase difference between the two divided signals.

Claims (1)

[Claims] A video signal is frequency modulated, this frequency modulated signal is divided into two signals whose frequency is 1/2 and the phase is shifted by a predetermined value, and these two divided signals are divided into two signals having the same azimuth angle.
During playback, a frequency portion of the two signals corresponding to a specific level of the video signal is extracted from the two heads, and the phase difference between the two extracted signals is set to the predetermined value. A video signal recording and reproducing device configured to perform correction so that the following is achieved.