JPS5932036B2 - Video signal reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a color signal in a video signal recorded in such a manner that frequency interleaf occurs between adjacent tracks is transmitted to the adjacent tracks by using a comb filter having a delay circuit. The present invention relates to a video signal reproducing device that removes crosstalk components from tracks.

A video signal recording/reproducing device (for example, a VTR) that greatly increases the recording density by forming adjacent tracks on a magnetic tape without forming so-called guard pads during recording. be.

During reproduction, a comb filter having a delay circuit capable of delaying the input signal by one horizontal period is used to effectively remove crosstalk components from adjacent tracks. Fig. 1 is a schematic diagram showing a rotary magnetic head device for the recording/reproducing system of such a VTR, and Fig.
Head H showing the angle of inclination of the head gaps gA and gB of the rotating magnetic heads HA and HB in the figure with respect to the scanning direction, respectively.
A and HB are perspective views, and FIG. 3 is a partially detailed view showing a pattern of tracks formed on the magnetic tape 1 by the rotary magnetic head device shown in FIG. As shown in FIG. 1, a head drum 2 of a rotating magnetic head device includes two rotating magnetic heads HA and HB arranged at an interval of 1800 degrees.

Then, the magnetic tape 1 is attached to the tape guide drum 3 by approximately 180 degrees.
The vehicle is guided diagonally in an Ω shape over an angular range of 0 and travels at a constant speed. As shown in Figure 2, these heads HA
, HB head gap gA, scanning direction of gB (arrow A
The angle of inclination (azimuth) with respect to the direction) is made to be different from each other. By running the tape 1 at a constant speed in this manner and rotating the head drum 2 at the frequency of H of the vertical synchronization signal, the magnetic tape 1 is scanned diagonally for one field, as shown in FIG. Video signal tracks 4a, 4b are formed for each. and each track 4a
, 4b are recorded adjacent to each other or partially overlapping each other without a guard pad between them.
FIG. 4 is a block circuit diagram of a recording/reproducing system of a conventional VTR.

Further, FIG. 5 is a graph showing the waveforms of each part of FIG. 4 and the vectors of each signal. In FIG. 4, a composite video signal Sa to be recorded is supplied to an input terminal 6 of the recording system. This composite video signal Sa is supplied to a low pass filter 7,
Here, the luminance signal component Sy is separated. The separated luminance signal Sy is supplied to the AGC circuit 8, where its amplitude is controlled to be constant. The output signal of this AGC circuit 8 is supplied to a clamp circuit 9, where it is clamped at a predetermined level. The clamped luminance signal Sy is FM
The high frequency band (for example, 3.
5 to 4.8 MHz) into a modulated luminance signal Sm. This modulated luminance signal Sm is supplied to a mixer 13 via a high-pass filter 11 and a recording amplifier 12. On the other hand, the composite video signal Sa supplied to the input terminal 6 is passed through a band pass filter 15 in the 3.58 MHz band.
The chroma signal component Sc is separated here.

The separated 3.58 MHz chroma signal Sc is supplied to the frequency converter 16 and converted into a 688 kHz low-frequency converted chroma signal Sl located below the frequency band of the above-mentioned modulated luminance signal Sm. This low frequency converted chroma signal Sl
is supplied to the mixer 13 through a low-pass filter 17 and a recording amplifier 18. In this mixer 13, the low frequency converted chroma signal Sl and the above-mentioned modulated luminance signal Sm are mixed, and this mixed signal is supplied to the magnetic heads HA and HB of the rotating magnetic head device through the REC contact of the recording/reproducing switch 14. be done. As a result, tracks 4a and 4b are formed as shown in FIG. 3, and the video signal is recorded there. Further, during this recording, the luminance signal Sy that has passed through the low-pass filter 7 is supplied to the sync separation circuit 22 via the REC contact of the recording/reproduction changeover switch 21, where the horizontal sync signal H is separated. This horizontal synchronizing signal H is supplied to the AFC circuit 23, and the frequency of 3.58MHz+(44-%)FH24.
A 27 MHz signal Se is formed. However, FH is the horizontal frequency, and (44-%) FH is the above-mentioned chroma signal Sc.
(3.58 MHz) with a low conversion frequency of 688 KHz. This signal Se is supplied to the contact 26a of the switch 26, and after its phase is inverted by the phase inversion circuit 25, it is supplied to the contact 26b of the switch 26. The movable contact of switch 26 is driven by the output of OR circuit 27. The output signal of the flip-flop 24 is supplied to one input terminal of the OR circuit 27. A synchronous separation circuit 2 is connected to the trigger input terminal T of this flip-flop 24.
A horizontal synchronization signal H separated by 2 is provided. Therefore, the flip-flop 24 is alternately inverted every 1H, and this inverted signal is supplied to the OR circuit 27. Further, a pulse PG obtained by detecting the rotational phase of the head drum 2 is supplied to another input terminal of the OR circuit 27. This pulse PG is, for example, a signal that is at a low level while the head HA is scanning the tape 1 (A field) and is at a high level while the head HB is scanning (B field). Therefore, from the output of the OR circuit 27, the fifth
A switch signal Sd shown in FIG. Sd is obtained, and the switch 26 is driven based on this switch signal Sd. That is,
In the A field, switch 26 is changed every 1H, and the B
In the field, the switch 26 is fixed to the contact 26a.

Therefore, in A field, 4.27M of AFO circuit 23
A Hz signal Se and an inverted signal Se of this signal are alternately supplied to the frequency converter 16 as a conversion carrier every 1H. Further, in the B field, the signal Se is supplied as a conversion carrier. Therefore, the phase of the low frequency converted chroma signal Sl converted from the 3.58 MHz Cucoma signal Sc to the low frequency of 688 KHz by the frequency converter 16 is different in the B field as shown by the arrow in FIG. 5 Sl. In the A field, signals of the same phase become signals whose phase is alternately inverted every 1H. As a result, as shown in FIG. 3, in the A track 4a, the chroma signal Sl whose phase is alternately inverted every 1H, and in the B track, the chroma signal Sl with the same phase is applied to the modulated luminance signal Sm. recorded as.

The chroma signal whose phase is alternately inverted every 1H and the chroma signal which is not inverted are the signals recorded on the A track and B track whose frequency bands are adjacent to each other by % of the horizontal frequency FH. We have a relationship of During reproduction, the rotation of heads HA and HB is controlled so that the rotary head device tracks the same tracks 4a and 4b as during recording.

The reproduction signals taken out from the heads HA and HB are supplied to a high-pass filter 30 via a reproduction amplifier 29.
Here, the modulated luminance signal Sm is separated from the reproduced signal.
As shown in FIG. 3, when recording, the adjacent tracks 4a and 4b are not provided with a guard band, but are placed adjacent to each other or partially overlapped, and between the heads HA and HB. Each is recorded with a different azimuth. Therefore, when head HA scans track 4a, it scans part of track 4b, and head HB also scans part of track 4b.
When scanning track 4b, even if it scans a part of track 4a, since the recorded modulated luminance signal Sm is a high frequency signal (3.5 to 4.8 MHz), different tracks and heads may be scanned. Azimuth loss occurs between the tracks and crosstalk from adjacent tracks is eliminated. The modulated luminance signal Sm separated by the high-pass filter 30 is supplied to a dropout compensation circuit via a limiter 31.

This compensation circuit is for compensating for the modulated luminance signal Sm that is temporarily absent due to scratches or dust on the magnetic tape 1, or due to clogging or wear and tear of the heads HA and HB. This dropout compensation circuit is composed of a dropout detection circuit 32, a changeover switch 33, a buffer amplifier 34, and a 1H delay line 35. The output signal of the limiter 31 is supplied to a contact 33a of a changeover switch 33 and also to a dropout detection circuit 32. The signal of the movable contact terminal of the switch 33 is sent to the buffer amplifier 34.
The input signal is supplied to the FM demodulator 36 via
The signal is fed back to the contact 33b of the switch 33 via a 1H delay line 35 that can be delayed by a horizontal period. The dropout detection circuit 32 is composed of, for example, an envelope detection circuit and a Schmitt trigger circuit, and is configured to detect the modulated luminance signal Sm.
When the envelope falls below a predetermined level (dropout), the output of this detection circuit 32 becomes 01'', and the movable contact of the switch 33 is pushed to the contact 33b side. , the normal signal from 1H before is transferred from the 1H delay line 35 to the contact 3 of the switch 33.
3b, and is supplied to the FM demodulator 36 via the buffer amplifier 34. The dropout-compensated modulated luminance signal Sm is demodulated into a luminance signal Sy by an FM demodulator 36, and after its carrier component is removed by a low-pass filter 37, it is supplied to a mixer 38.

On the other hand, the reproduction signal obtained from the reproduction amplifier 29 is also supplied to a low-pass filter 39, where the low-pass converted chroma signal Sl contained in the reproduction signal is separated. This low-pass converted chroma signal Sl is supplied to the frequency converter 40, where it is converted from the low-pass converted frequency (688 KHz) to a reproduced chroma signal Sf of the color subcarrier frequency (3.58 MHz). In this case, the same switch signal Sd (Sd in FIG. 5) used during recording is used as the conversion carrier supplied to the frequency converter 40. However, during reproduction, this switch signal Sd is formed based on the horizontal synchronization signal H in the reproduction luminance signal Sy supplied from the limiter 37 to the synchronization separation circuit n through the PB contact of the changeover switch 21. As a result, the phases of the reproduced chroma signal Sf are aligned in the same direction in both the A field and the B field, as shown in FIG. 5 Sf. Note that since the reproduced low-frequency converted chroma signal Sl is in the low frequency range (688 KHz), the effect of crosstalk removal due to the azimuth loss of the heads HA and HB cannot be obtained like the above-mentioned modulated luminance signal Sm in the high frequency range. .

Therefore, the reproduced low-pass converted chroma signal Sl obtained from the low-pass filter 39 is as shown in FIG. 5 Sl (A field).
and S/l (B field), the main signal (solid line) includes a crosstalk component (dotted line) from the adjacent track. Therefore, the 3.58 MHz chroma signal Sf converted by the frequency converter 40 is expressed as shown in FIG.
As shown in A field) and Sf (B field), the main signals (solid lines) of both the A field and B field are in the same phase, and the crosstalk components (dotted lines) are inverted every 1H. That is, a crosstalk component that is frequency interleaved with the chroma signal Sf is mixed with the chroma signal Sf. In the above explanation, in order to simplify the explanation, it is assumed that the chroma signal Sf is in phase every 1H, and the phase of the crosstalk component is inverted every 1H. However, in reality, due to frequency interleaving in the NTSC system, the chroma signal (
The solid line) originally has a phase inversion every 1H, so
Crosstalk components (dotted lines) appear in phase. The output signal of the frequency converter 40 is supplied to a comb filter consisting of a 1H delay line 41 and a subtracter 42, where crosstalk components are removed from the chroma signal Sf'.

That is, the signal Sg that has passed through the 1H delay circuit 41 is a signal as shown in FIG. By subtracting , a reproduced chroma signal Sh without crosstalk can be obtained as shown in FIG. 5 Sh. The reproduced chroma signal Sh and the previously described reproduced luminance signal Sy are mixed by the mixer 38 and then supplied to the output terminal 43, and further supplied to the television receiver as a reproduced composite video signal. The VTR configured as described above is provided with a circuit that compensates for dropouts of reproduced video signals.

This dropout compensation circuit uses an expensive 1H delay line 35, and as mentioned above, another delay line 41 having the same function is used to remove crosstalk components from the color signal. There is. For this reason, conventional TR
However, there was a problem that the overall cost was high. The present invention has been made in view of the above-mentioned problems, and is designed so that a delay circuit such as a delay line of a comb filter for removing crosstalk components from color signals is also used in a dropout compensation circuit. There is.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 6 is a VTR showing an embodiment in which the present invention is applied to a TR.
FIG. 3 is a block circuit diagram of a playback system. In FIG. 6, the same parts as in FIG. 4 are given the same reference numerals. In the embodiment shown in FIG. 6, the 1H delay line 35 of the dropout compensation circuit of FIG.
H delay line 41 is shared.

That is, in the chroma signal reproducing system, the head HA is
, HB, a reproduction amplifier 29, a low-pass filter 39, and a frequency converter 40, a reproduction chroma signal Sf of 3.58 MHz is reproduced. The reproduced chroma signal Sf is supplied through a mixer 45 to a comb filter consisting of a 1H delay line 41 and a subtracter 42, where its crosstalk components are removed, and then supplied to a mixer 38. In the luminance signal reproduction system, the luminance signal Sy is reproduced through a reproduction amplifier 29, a high-pass filter 30, a limiter 31, an FM demodulator 36, and a low-pass filter 37.

If the luminance signal Sy does not have a dropout portion, the luminance signal Sy is supplied to the mixer 38 through the contact 33a of the switch 33, where it is mixed with the reproduced chroma signal and then supplied to the output terminal 43. The luminance signal Sy is also supplied to the AM modulator 47. This AM modulator 47 includes, for example, a 3.58 MHz modulation carrier F.
c is supplied, and the modulation carrier Fc is amplitude-modulated in accordance with the amplitude of the luminance signal Sy. The AM modulated luminance signal is
The signal is supplied to a mixer 45, where it is mixed with the chroma signal Sf, and then supplied to a 1H delay line 41, where it is held for one horizontal period. In this case, 3.58M
Hz reproduced chroma signal Sf' and 3.58 MHz (7) A
Since the signal is mixed with the M modulated carrier and held in the 1H delay line 41, it is necessary to extract these signals separately.

FIG. 7 is a graph showing the output characteristics of the comb filter 1. From the C-shaped comb filter 1, which consists of the 1H delay line 41 and the subtracter 42 in FIG. 6, the output shown by the solid line in FIG. can get. Further, an output shown by a dotted line in FIG. 7 is obtained from a Y-shaped comb filter consisting of a 1H delay line 41 and an adder 46. That is, from the subtracter 42, 3.58 MHz
A chroma signal having a frequency band for each horizontal frequency FH is separated and obtained around the color subcarrier liquid. As mentioned above, the crosstalk component that has a frequency interleaf relationship with this chroma signal is located in the valley of the output characteristic of the C-shaped comb filter 1, so the crosstalk component is removed from the chroma signal output from this filter 1. has been done. Therefore, if the AM modulated luminance signal mixed with the chroma signal in the mixer 45 is set in a frequency interleaf relationship with the chroma signal, the subtracter 4 of the C-shaped comb filter
From the adder 46 of the Y-shaped comb filter 1, an AM modulated luminance signal not mixed with the chroma signal is separated and obtained. can get. In order to create a frequency interleaf relationship between the AM modulated luminance signal and the chroma signal in this way, as shown in FIG.
is supplied with a modulated carrier whose phase is inverted every 1H.

That is, for example, a modulated carrier Fc of 3.58 MHz is supplied to the contact 50a of the switch 50, and a signal obtained by inverting the phase of this carrier by the phase inverting circuit 49 is supplied to the switch 50.
is supplied to contact 50b. The switch 50 is driven, for example, by the output of the flip-flop 24 of FIG. 4, so as to switch between the contacts 50a and 50b every 1H. Therefore, the AM modulator 47 is supplied with a modulated carrier obtained by inverting the phase of the carrier Fc every 1H (that is, at a period of 2/FH). As a result, when the luminance signal is AM-modulated based on this modulated carrier, the frequency spectrum of the AM-modulated luminance signal is offset from the FH position of the carrier Fc to a position that is an odd multiple of 1 (dotted line arrow in FIG. 7).

As a result, the AM modulated luminance signal is recorded in the 1H delay line 41 in a frequency interleaved relationship with the chroma signal.

Since the AM modulated luminance signal stored in this 1H delay line 41 is located at the peak of the output characteristic of the Y-shaped comb filter 1 (dotted line in Figure 7), the adder 46 of the Y-shaped comb filter 1 This AM modulated luminance signal can be extracted from the chroma signal separately from the chroma signal. In this case, as mentioned above, the crosstalk component of the chroma signal exists in the valley of the output characteristic of the C-shaped comb filter (solid line in Figure 7), so this crosstalk component is reflected in the AM modulation luminance. There is a risk that it may be mixed into the signal. However, this crosstalk component is at a level about -10 dB lower than the chroma signal even when the tracking deviation between heads HA and HB is maximum, so the amplitude of the AM modulated luminance signal must be made sufficiently large compared to the crosstalk component. For example, the SN ratio of the luminance signal will not deteriorate. The output signal of adder 46 is provided to AM demodulator 48 .

This AM demodulator 48 is supplied with the same carrier as the AM modulator 47 as a demodulation carrier. Therefore, the original reproduced luminance signal Sy is demodulated by the AM demodulator 48, and this reproduced luminance signal Sy is supplied to the contact 33b of the switch 33. Note that when there is a dropout in the reproduced luminance signal Sy, this dropout is detected by the dropout detection circuit 32, and the switch 33 is activated in accordance with this detection output.
is brought down to the contact point 331) side.

Therefore, the luminance signal Sy of 1H before without dropout is supplied to the mixer 38 through the contact 33b of the switch 33. Then, in this mixer 38, the chroma signal obtained from the subtracter 42 of the C-shaped comb filter and the luminance signal are mixed, and the output terminal 43 receives the signal as a composite video signal.
supplied to Note that when dropout occurs over several H times, the luminance signal Sy is transmitted to the AM modulator 47,
The signal circulates through the mixer 45, the 1H delay line 41, the adder 46, the AM demodulator 48, and the contact 33b of the switch 33, and this circulating signal is supplied to the mixer 38 over the number H described above. As described above, the present invention provides a comb filter for frequency-converting a luminance signal in a reproduced video signal so as to perform frequency interleaf with respect to a color signal, and then removing crosstalk components from the color signal together with the color signal. The luminance signal supplied to one delay circuit and stored in this delay circuit is taken out from the comb filter 1 separately from the color signal and used as a luminance signal to compensate for dropout of the reproduced video signal.

Therefore, the delay circuit of the comb filter for removing crosstalk components from the color signal can also be used as the delay circuit of the dropout compensation circuit, and therefore the video signal reproducing apparatus can be constructed at a lower cost.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a rotary magnetic head device in the recording/reproducing system of a conventional VTR, and FIG. 2 is a schematic diagram showing the rotary magnetic head HA of FIG.
, HB, a third perspective view of the heads HA and HB showing the angle of inclination of the head gaps GA and gB with respect to the scanning direction.
The figure is a partial detailed view showing a track pattern formed on a magnetic tape by the rotating magnetic head device shown in FIG. 1, and FIG. 4 is a block circuit diagram of a conventional TR recording/reproducing system.
FIG. 5 is a graph showing the waveforms of each part of FIG. 4 and the vectors of each signal. FIG. 6 is a block circuit diagram of a reproduction system of a VTR showing an embodiment applied to a VTR, and FIG. 7 is a graph showing output characteristics of a comb filter. In the symbols used in the drawings, 1 is a magnetic tape, 2 is a head drum, 3 is a tape guide drum, and 4a and 4b are video signal tracks.

Claims (1)

[Claims] 1. Crosstalk components from the adjacent tracks are removed by using a comb filter having a delay circuit from the color signals in the video signals recorded in such a manner that the frequencies are interleaved with each other between adjacent tracks. In the video signal reproducing device, the luminance signal in the reproduced video signal is frequency-converted so as to be frequency interleaved with the chrominance signal, and then is supplied together with the chrominance signal to the delay circuit of the comb filter. The luminance signal and the color signal are individually extracted from the comb-shaped filter, and when a dropout is detected from the video signal, the luminance signal extracted from the comb-shaped filter is extracted from the comb-shaped filter. A video signal reproducing device configured to be used as a luminance signal for out compensation.