JP3123069B2 - Video tape recorder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a video tape recorder, and more particularly to a video tape recorder intended to obtain a good reproduced image.

[Conventional technology]

Two magnetic heads are mounted 180 degrees opposite to the drum rotating at the frame frequency, and the two magnetic heads alternately record color video signals on the magnetic tape that runs diagonally around the drum. A VTR for reproducing a color video signal is known.

In such a VTR, a luminance signal is FM-modulated, a chrominance signal is converted into a low-frequency carrier frequency, and a signal obtained by frequency-multiplexing the FM-modulated luminance signal and the low-frequency conversion chrominance signal is recorded on a magnetic tape. .

On the reproduction side, the FM-modulated luminance signal is FM-demodulated, and the low-frequency conversion chrominance signal is frequency-converted to the original subcarrier frequency.

The color signal processing circuit on the reproduction side is provided with an APC (automatic phase control) circuit for canceling phase fluctuations caused by unevenness in running speed of the magnetic tape or the like during frequency conversion. The APC circuit generates a carrier signal for conversion having a phase variation similar to that of the burst component in the reproduced low-frequency conversion color signal, and this carrier signal is used for frequency conversion of the low-frequency conversion color signal. You.

[Problems to be solved by the invention]

When the low-frequency conversion color signal reproduced by the magnetic head is reproduced by the same magnetic head, the phase fluctuation has continuity, and the phase fluctuation can be removed by the APC.

However, when one magnetic head and the other magnetic head are switched, the heads are different,
There is a problem that the phase of the color burst signal becomes discontinuous before and after the switching timing due to the absence of the color burst signal during the period of the equalizing pulse or the vertical synchronization signal after the switching timing.

As a result, there is a problem that the control of the APC is not performed normally during the period from the switching timing to the lock of the APC, and the phase of the color burst signal of the reproduced color video signal during this period is disturbed.

When a reproduced color video signal in which the phase of the color burst signal is disturbed as described above is supplied to the monitor,
Since the APC error of the monitor becomes large, the hue of the color signal is disturbed for a while after the switching timing, and there is a problem that the disturbed hue occurs at the upper part of the monitor screen.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a video tape recorder capable of preventing discontinuity of a color burst signal before and after switching between two magnetic heads and obtaining a good reproduced image.

[Means for solving the problem]

The present invention relates to a video tape recorder in which first and second magnetic heads provided on a rotating drum alternately take out a reproduction signal from a magnetic tape and obtain a color signal from the reproduction signal. Delay means for delaying and feeding back the separated color signal converted to the original subcarrier frequency and the first and second color signals in the reproduced signal;
Means for replacing the color burst signal in the color signal with the delayed color burst signal for a predetermined period within the vertical synchronization blanking period from the switching timing of the magnetic head.

[Action]

Reproduction signals are alternately taken out of the magnetic tape by the first and second magnetic heads provided on the rotating drum.

Then, a color signal separated from the reproduced signal and converted to the original subcarrier frequency is formed.
Feedback is delayed.

When the first and second magnetic heads are switched, during the period from the switching timing of the first and second magnetic heads in the reproduction signal to the equalization pulse, the color burst signal is delayed by 1H in the previous field. It is replaced with a color burst signal.

In addition, a non-delayed color burst signal is selected except for a predetermined period when the magnetic head is switched.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

In the configuration shown in FIG.
The reproduced signal alternately reproduced by the two magnetic heads provided opposite to each other at ゜ is supplied to the bandpass filter 2 via the terminal 1.

The band-pass filter 2 separates the low-frequency conversion color signal from the reproduced signal described above, and supplies the low-frequency conversion color signal to the ACC circuit 3.

The ACC circuit 3 controls the amplitude level of the low-frequency conversion color signal so as to be a predetermined amplitude level, and then supplies the same to the frequency converter 4.

In the frequency converter 4, the low-frequency conversion chrominance signal whose carrier frequency is, for example, 743 kHz, and the frequency supplied through the carrier inverting circuit 31 (4.32 MHz)
Is multiplied by the carrier signal
An output signal centered on the frequency of z is formed, and this output signal is supplied to the bandpass filter 5.

The bandpass filter 5 extracts, from the output signal from the frequency converter 4, a reproduced color signal in the vicinity of 3.58 MHz, that is, a reproduced color signal in the range of (3.58 MHz ± 500 KHz) in the case of the NTSC system. This reproduced color signal is 1H (H:
(Horizontal period) is supplied to a comb filter 6 using a delay line.

The structure of the comb filter 6 is shown in FIG. In the configuration shown in FIG. 2, the comb filter 6 is 1H
A simple comb filter 10 is constituted by the delay circuit 8 and the adder circuit 9 having the above-mentioned delay amount, and a feedback comb filter 11 is constituted by the switch 7 and the delay circuit 8.

In the comb filter 6, for example, a period Tc of 3.5H from the change point SW of the switching pulse SWP shown in FIG. 6A to the start point PST of the vertical blanking period VBLK.
The feedback comb filter 11 is formed by controlling a switch control signal SSW of a switch 7 described later. Therefore, in the example shown in the figure, 1H before, the color burst signal CBST0 in the previous field is fed back to the terminal 7b of the switch 7 so that the color burst signal CBST0 in the previous field is fed back as shown in FIGS.
Is selected and taken out from the terminal 24, so that the color burst signal CBST in the period Tc is replaced. As a result, as shown in FIG. 6E, the timing of switching the magnetic head, that is, the continuity of the phase of the color burst signal CBST before and after the change point SW is ensured.

In the comb filter 6, the switch 7 is controlled during the period other than the period Tc, so that the simple comb filter 10 is formed. Therefore, by combining the color signal C0 of the previous H and the color signal C1 of the current H, the crosstalk component from the adjacent track is removed.

Color signal C in the current field via terminal 120
1. The color burst signal CBST1 is supplied to the terminal 7a of the switch 7.

This switch 7 is connected to a change point S of the switching pulse SWP.
From W to the vertical blanking period VBLK, for example, 3.
It is provided to replace the color burst signal CBST in the period Tc of 5H. The connection state of the switch 7 is controlled based on a switch control signal SSW supplied from the switch control circuit 12. When the switch control signal SSW is at a high level, for example,
7a and 7c are connected, and when low level, terminals 7b and 7c
Are connected. The color signal and the color burst signal CBST that have passed through the switch 7 are supplied to a delay circuit 8 and an addition circuit 9.

The color signal before 1H and the color burst signal CBST output from the delay circuit 8 are fed back to the switch 7.
And the adder 9.

FIG. 2 shows the configuration of the switch control circuit 12 for forming the above-mentioned switch control signal SSW.

In the configuration shown in FIG.
The switching pulse SWP shown in FIG. A is a monostable multivibrator (hereinafter referred to as a monomulti).
Supplied to 5,16.

As shown in FIG. 3A, the switching pulse SWP is
The pulse of the frame period in which the level is inverted in the field Ta where the reproduction signal of one magnetic head exists and in the other field Tb where the reproduction signal of the other magnetic head exists. This switching pulse SWP is formed from an output signal of a rotation detector that detects the rotation phase of the rotating drum.
The rising edge and the falling edge of the switching pulse SWP are change points SW.

The monomulti 15 is triggered by the rising edge of the switching pulse SWP, and the monomulti 15 outputs a pulse PS1 having a pulse width of 3.5H shown in FIG. 3B. The falling edge of the switching pulse SWP triggers the monomulti 16, and the monomulti 16 outputs a pulse PS2 having a pulse width of 3.5H as shown in FIG. 3C. PS2 is supplied to the OR gate 17.

The OR gate 17 outputs a pulse PS3 shown in FIG. 3D formed by the logical sum of the pulses PS1 and PS2 output from the monomultis 15 and 16. This pulse PS3 is
As shown in FIG. D, during one field, the signal is at a high level only during a period Tc of 3.5H from the transition point SW, and thereafter becomes a low level, and is supplied to the inverter 18.

In the inverter 18, the level of the pulse PS3 is inverted to form a pulse PS30 as shown in FIG.
It is supplied to the OR gate 19. The pulse PS30 is formed in one field cycle corresponding to the switching pulse SWP, and a period Tc having a pulse width of 3.5H is provided at the beginning of each cycle.

The level of the horizontal synchronizing signal HSY separated from the reproduced luminance signal is supplied to the terminal 20 as shown in FIG. 4A, and the horizontal synchronizing signal HSY is supplied to the low-pass filter 21.

In the low-pass filter 21, the horizontal synchronizing signal HSY
Is delayed and supplied to the inverter 22 for a period substantially equal to the pulse width of the horizontal synchronizing signal HSY.

In the inverter 22, the level of the horizontal synchronizing signal HSY is inverted to form a burst gate pulse PBG as shown in FIG. 4B. This burst gate pulse PBG is supplied to the OR gate 19.

In the OR gate 19, a logical sum of the pulse PS30 supplied from the inverter 18 and the burst gate pulse PBG supplied from the inverter 22 is obtained, and a switch control signal SSW as shown in FIG. 5A is formed.

This switch control signal SSW is formed in one field cycle. As shown in FIG. 5A, a burst gate pulse PBG is inserted in a period Tc corresponding to the first 3.5H in one field period. I have.

FIG. 5B shows details in the above-mentioned period Tc.

Burst gate pulse PBG inserted during period Tc
Is set to a low level at the timing when the color burst signal CBST separated from the reproduction signal shown in FIG. 5C is supplied. As a result, the switch control signal SSW becomes low level, and the terminals 7b and 7c of the switch 7 are connected, so that the comb filter 6 forms the feedback comb filter 11 as described above. Therefore, in the feedback comb filter 11, the color burst signal CBST0 of the previous field is fed back via the switch 7 1H before, in the example shown in FIG. Is done.

FIG. 6 shows the replacement of the color bust signal CBST in the period Tc.

FIG. 6A shows the switching timing of the magnetic head and the vertical blanking period VBLK. The switching timing, that is, 3.5H period from the change point SW to the start point PST of the vertical blanking period VBLK, the vertical blanking period VBLK after the start point PST, and the content is the vertical synchronization period of 3H The period of the equalization pulse PEQ is provided 3H before and after the signal VD.

6B to 6E show the feedback comb filter 11.
The effect of is shown. That is, when the magnetic head is switched at the change point SW, the color signal C1 of the current field and the color burst signal CBST1 are supplied to the main line system 24 of the color signal in the comb filter 6.

In the prior art, as shown in FIG.
, The color burst signal CBST1 of the current field is selected and supplied to the APC detection circuit 25. in this case,
If the continuity of the phase between the color burst signal CBST0 of the previous field and the color burst signal CBST1 of the current field is not satisfied, AP
Until C locks, APC control is not normal,
The phase of the color burst signal CBST of the reproduced color video signal is disturbed. That is, since the color signal C1 and the color burst signal CBST1 of the current field are supplied during a period of 3.5H from the timing of the change point SW of the magnetic head, the phase error in the APC is particularly large. Therefore, if this is improved, a great effect can be expected.

As described above, the change point SW of the switching pulse SWP
In the period Tc of 3.5 to 3.5H, the comb filter 6 constitutes the feedback comb filter 11, so that the color burst signal CBST0 of the previous field changes at the timing of the burst gate pulse PBG shown in FIG. 6D. 3.5H after point SW
, And is supplied to the APC detection circuit 25.

In FIGS. 6B, 6C and 6E, after the pause period shown by the solid line, the switch 7 is controlled to supply the reproduced color burst signal CBST1 of the vertical blanking period VBLK. This color burst signal CBS
Based on T1, the APC detection circuit 25 forms a carrier signal for canceling phase fluctuation. As described above, the color burst signal CBST1 of the current field is not immediately supplied to the APC detection circuit 25 at the timing of the change point SW, and the 3.5T period T
Since c supplies the color burst signal CBST0 of the previous field to the APC detection circuit 25 and supplies the color burst signal CBST1 of the current field to the APC detection circuit 25 after the pause, as shown in FIG. 6E. Then, the continuity of the phases of the color burst signals CBST0 and CBST1 in the two adjacent fields is satisfied.

As a result, the continuity of the phases of the color burst signals CBST0 and CBST1 before and after the change point SW between the previous field and the current field is satisfied, so that the control of the APC during the period from the switching timing to the lock of the APC is achieved. Is normally performed without being disturbed, and the occurrence of disturbance in the phase of the color burst signal of the reproduced color video signal during this period can be prevented.

Then, even if the obtained reproduced color video signal is supplied to the monitor, it is possible to prevent the hue of the color signal from being disturbed due to an increase in the APC error of the monitor, and to prevent the disturbance of the hue at the upper portion of the monitor screen.

From the comb filter 6, the reproduced color signal from which the crosstalk has been removed in periods other than the period Tc is subjected to the noise reduction 26,
The signal is supplied to the APC detection circuit 25, and in the period Tc, the color burst signal CBST satisfying the phase relationship is supplied to the noise reduction 26 and the APC detection circuit 26.

The noise reduction 26 is formed by a feedback comb filter (not shown), and a reproduced color signal is extracted from a terminal 27.

In FIG. 1, a luminance signal processing circuit including an FM demodulation circuit, a de-emphasis circuit, and the like is omitted. Output terminal 27
Are mixed with the reproduced luminance signal from the luminance signal processing circuit.

In the APC detection circuit 25, the phase of the frequency (3.58 MHz) of the burst signal of the color signal supplied from the comb filter 6 is compared with the reference signal of (3.58 MHz) supplied from the reference signal generation circuit 28, Phase error is VCO2 as control voltage
Supplied to 9.

The oscillation frequency of the signal output from the VCO 29 changes based on the above-described phase error, but the center frequency is 743 KHz. This signal is supplied to the frequency converter 30.

The VCO 29 forms a carrier signal having the same phase variation as the reproduced color signal, and supplies the carrier signal to the frequency converter 30.

In the frequency converter 30, the reference signal is supplied from a reference signal generating circuit 28 which is a crystal oscillator having a stable oscillation frequency (3.58 MHz
The reference signal of z) is multiplied by the carrier signal supplied from the VCO 29 to form a carrier signal having a frequency of (4.32 MHz). The carrier signal is supplied to the carrier inverting circuit 10.

The carrier inverting circuit 31 performs the following processing.

The video signal is, for example, PI
(Phase Invert) format. Therefore, the carrier inverting circuit 31 performs a process of inverting the phase of the carrier signal in one of two adjacent tracks and not inverting the phase of the carrier signal in the other track. Therefore, control is performed to invert the phase of the carrier signal corresponding to the color signal reproduced in one of the channels every 1H.

Since the carrier signal subjected to the above-described carrier inversion processing is supplied to the frequency converter 4, the color signal component and the crosstalk component of the output signal from the frequency converter 4 are inverted in phase every 1H. By this phase inversion processing, crosstalk from an adjacent track is removed in the comb filter 6 at the subsequent stage.

Further, the carrier signal whose frequency is (4.32 MHz) includes a reference signal supplied from the reference signal generation circuit 28,
Since the chrominance signal is formed by phase comparison with the color burst signal CBST, the chrominance signal is a signal phase-locked to the reference signal.

FIG. 7 shows a waveform near a change point SW at which the reproduced signals of the two magnetic heads are switched. The change point SW is set, for example, at a position 6.5H from the beginning of the vertical synchronization signal VD.

A period of the equalization pulse PEQ exists before and after the vertical synchronization signal VD. Since the color burst signal CBST cannot be inserted during the period of the equalization pulse PEQ and the vertical synchronization signal VD,
The color burst signal CBST is replaced during a period indicated by Tc from the change point SW to before the equalization pulse PEQ, for example, 3.5H.

According to this embodiment, the phase of the color burst signal CBST is changed by using the comb filter 6 for canceling crosstalk and the comb filter 6 for canceling crosstalk among the comb filters 6 constituting the noise reduction 26. Although it is made continuous to satisfy the continuity of the phase between two adjacent fields, the present invention is not limited to this. For example, a comb filter constituting the noise reduction 26 may be used. In this case, the switch control signal SSW from the switch control circuit 12 must be supplied to the noise reduction 26.

According to this embodiment, the period T from the change point SW of the switching pulse SWP to the vertical blanking period VBLK is obtained.
c, the color burst signal CBST is replaced. However, the present invention is not limited to this.
In addition to Tc, the color burst signal may be replaced between the period of the equivalent pulse and the period before the video signal is inserted.

Further, according to the embodiment, the replacement period Tc of the color burst signal is described as 3.5H. However, the present invention is not limited to this. Replacement may be performed.

Further, according to this embodiment, an example in which the present invention is applied to an NTSC color video tape recorder is shown, but the present invention is not limited to this. For example, a PAL color video tape recorder can be used. Is also applicable.

〔The invention's effect〕

According to the video tape recorder of the present invention, the period from the switching timing of the first and second magnetic heads to the equalizing pulse is replaced by the color burst signal delayed by 1H and fed back. There is an effect that the phase of the color burst signal can be prevented from becoming discontinuous before and after the timing. As a result, the control of the APC during the period from the switching timing to the lock of the APC is normally performed without being disturbed, and it is possible to prevent the occurrence of the disturbance of the phase of the color burst signal of the reproduced color video signal during this period. effective. Furthermore, when the above-mentioned reproduced color video signal is supplied to the monitor, it is possible to prevent the hue of the color signal from being disturbed due to an increase in the APC error of the monitor, and to prevent the occurrence of the hue disturbance at the upper part of the monitor screen. .

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a comb filter and a switch control circuit, and FIGS. 3 to 5 are waveform diagrams used to explain one embodiment. FIG. 6 is a diagram used for explaining the circuit operation, and FIG. 7 is a waveform diagram showing a one-field video signal. Description of main reference numerals in the drawings 6: comb filter, 7: switch, 8: delay circuit, 11: feedback comb filter, C0, C1: color signal, SW: transition point, VBLK: vertical blanking period, SSW: Switch control signal, Tc: period, PBG: burst gate pulse, CBST: color burst signal.

Claims (1)

(57) [Claims] 1. A video tape recorder wherein first and second magnetic heads provided on a rotating drum alternately take out a reproduction signal from a magnetic tape and obtain a color signal from the reproduction signal. Delay means for delaying and feeding back the color signal separated from the reproduction signal and converted into the original subcarrier frequency; and a blanking period for vertical synchronization from the timing of switching between the first and second magnetic heads in the reproduction signal. Means for replacing a color burst signal in the color signal with a delayed color burst signal for a predetermined period of time.