JPS5812796B2 - Carrier color signal regeneration circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When recording a luminance signal (monochrome video signal) on a magnetic tape or the like, the following method can significantly increase the recording amount.

That is, as shown in FIG. 1, the rotating magnetic heads 1A,
1B with an angular spacing of 180° from each other, and
The magnetic tape 2 is rotated at a speed of approximately 180 degrees, and the magnetic tape 2 is run obliquely along the tape guide drum 3 over an angular range of approximately 180 degrees.

In this case, as shown in FIG. 2, the width directions of the operating gaps ga and gb of the heads 1A and 1B, that is, the azimuth angles, are made different from each other.

Then, the brightness signal is converted into an FM signal that occupies the high frequency side of the recordable band, and this FM brightness signal is converted to the head 1A, 1.
Supply to B.

Therefore, according to such a recording method, one field of the luminance signal is recorded obliquely on the tape 2 as one magnetic track 4, as shown in FIG.
Since the azimuth angles of tracks 4A and 1B are different from each other, correspondingly, the azimuth angles of tracks 4A and 4B are different from each other.

Let us now consider the case where such a recording pattern is reproduced by the heads 1A and 1B.

Then, tracks 4A and 4B are created by heads 1A and 1B.
The FM brightness signal is reproduced from head 1, but in this case, head 1
A and track 4B have different azimuth angles, and head 1B and track 4A have different azimuth angles.
Since the FM brightness signal is recorded on the high frequency side, the FM brightness signal is recorded on the high frequency side, so there is no crosstalk between tracks due to azimuth loss.
M luminance signal can be reproduced.

Also, even if some crosstalk occurs between tracks,
Since the luminance signal is an FM signal, its crosstalk is suppressed by the limiter action of the playback system limiter.
Therefore, an FM luminance signal without inter-track crosstalk can be obtained.

In this way, there is no inter-track crosstalk in the reproduced FM luminance signal, so when recording, the third
As shown in the figure, there is no guard band between adjacent tracks 4A and 4B, or adjacent tracks 4A and 4B are
The FM luminance signal can be recorded so that 4B partially overlaps, and therefore the amount of recording can be greatly increased.

By the way, in order to magnetically record a color video signal, generally the luminance signal is converted to an FM luminance signal, and the carrier color signal is frequency-converted to the lower frequency side of the FM luminance signal, and the frequency-converted carrier color signal and The added signal with the FM luminance signal is magnetically recorded.

Therefore, when recording a color video signal using the recording method shown in FIGS. 1 to 3, it is conceivable to frequency-convert the carrier color signal to a low frequency band, add it to the FM luminance signal, and record the signal simultaneously.

However, simply recording in this way will not cause inter-track crosstalk for the luminance signal due to the azimuth loss of the reproducing head during playback, but since the carrier chrominance signal occupies a low frequency band, the carrier of the adjacent magnetic track will The azimuth loss of the reproducing head is small for color signals, and therefore inter-track crosstalk occurs in the carrier color signals.

Taking these points into consideration, the present invention is capable of reproducing color video signals recorded at high density without causing crosstalk between tracks, and furthermore, is capable of reliably reproducing even if there is noise or dropout. This is what we are trying to do.

An example of this will be explained below.

First, as shown in FIG. 3, the magnetic tape 2 has an NTS
One field of the C color video signal is recorded as one magnetic track 4, but the color video signal is recorded on the fourth magnetic track 4.
The signals Sa and Sb have frequency spectra as shown in the figure.

In other words. A luminance signal and a carrier color signal are separated from the NTSC color video signal, and the luminance signal is converted into an FM signal Sy that occupies the high frequency side of the band in which recording and reproduction is possible. During the period Ta, as shown in FIG. 4A, the carrier color signal has a carrier frequency fa.
is frequency-converted into a signal Sc, and this signal Sc and signal Sy
The multiplexed signal Sa is sent to track 4 by head 1A.
A, and in every other remaining field period Tb, the carrier color signal has a carrier frequency fb.
is frequency-converted into a signal Sc, and this signal Sc and signal Sy
The multiplexed signal sb is sent to track 4 by head 1B.
It is recorded on tape 2 as B.

In this case, the carrier color signal Sc in the signal Sa and the carrier color signal Sc in the signal sb have a frequency relationship such that they are interleaved with each other, that is, in this example, the carrier color signal Sc in the signal Sa and the carrier color signal Sc in the signal sb are interleaved with each other.

This tape 2 is then played back by the apparatus shown in FIG.

That is, the pulse generating means 6 is provided on the part that rotates together with the heads 1A and 1B, for example, the rotating shaft 5, so that the head 1A
, 1B, a pulse of 30 Hz is extracted, and this pulse is supplied to the servo circuit 7, and the tracking servo for the track 4 of the heads 1A, 1B is performed to control the heads 1A, 1B and the tracks 4A, 4B. The relationship with is the same as at the time of recording.

In this way, as shown in FIG. 6A, the field period Ta
, the head 1A reproduces the multiplexed signal Sa from the track 4A, and during the field period Tb, the head 1B reproduces the multiplexed signal Sa.
The multiplexed signal Sb is reproduced from the track 4B.

However, in this case, as mentioned above, the FM luminance signal Sy has a high occupied frequency band, so it can be extracted without causing inter-track crosstalk due to azimuth loss, but the carrier signal Sc has a low occupied frequency band, so it can be extracted. ,
A reduction in inter-track crosstalk due to azimuth loss, such as in the FM luminance signal Sy, cannot be expected, and as shown in FIG. At the same time, the carrier color signal with the carrier frequency fb from the adjacent track 4B is simultaneously reproduced as the crosstalk component Sk, and during the field period Tb, the carrier color signal with the carrier frequency fb is reproduced from the adjacent track 4B.
At the same time that the carrier color signal Sc of b is reproduced, the carrier color signal of carrier frequency fa from the adjacent track 4A is simultaneously reproduced as the crosstalk component Sk.

However, in this case, between adjacent tracks 4A and 4B,
The carrier frequencies of the carrier speed color signal Sc are fa and fb, and the carrier color signals Sc are interleaved with each other, so the crosstalk component Sk from the adjacent track is interleaved with respect to the original carrier color signal Sc. There is.

If the crosstalk component Sk is interleaved, the crosstalk component Sk can be removed by supplying the carrier color signal Sc to a C-shaped comb filter, thereby obtaining a carrier color signal Sc free of inter-track crosstalk. In the present invention, a color video signal is reproduced by paying attention to such points, and at the same time, the reproduction can be performed reliably even if there is noise or dropout during this reproduction.

That is, the reproduced signals from the heads 1A and 1B are supplied to the high-pass filter 12 through the reproduction amplifier 11, and then
The M luminance signal Sy is taken out, and this signal Sy is supplied to the normally closed input contact of the switch circuit 14 through the limiter 13, and is also supplied to the delay circuit 15 and delayed by one horizontal period before the normally open state of the switch circuit 14. The signal Sy supplied to the side input contact and also from the filter 12 is supplied to a dropout detection circuit 16 to detect dropout, and the detection signal is supplied to the switch circuit 14 as its control signal.

In this way, the signal Sy from the limiter 13 is taken out from the switch circuit 14 when there is no dropout, and the signal Sy from the delay circuit 13 is taken out when there is a dropout.
5, the delayed signal Sy is taken out to compensate for the dropout of the signal sy.

This dropout-compensated signal Sy is then supplied to the demodulation circuit 17 to demodulate the luminance signal, and this luminance signal is supplied to the addition circuit 18.

Furthermore, the carrier color signal Sc reproduced simultaneously with the luminance signal is frequency-converted to the original carrier frequency fs, and the inter-track crosstalk component Sk is removed.

That is, the signal from the amplifier 11 is supplied to the low-pass filter 21, and as shown in FIG. 6B, a carrier color signal Sc having a crosstalk component Sk is extracted. At the same time, an alternating signal Ss is supplied from the switch circuit 42 to the converter 22.

The details of how to form this signal Ss will be described later, but
As shown in FIG. 6C, this signal Ss is a signal whose frequency is (fs+fa) during the field period Ta and whose frequency is (f5+fb) during the field period Tb.

Therefore, in the converter 22, as shown in FIG. 6D, the carrier frequency is the original frequency fS in any field period, and the carrier frequency of the crosstalk component Sk is (fs-1 /2fh)
and (fs+1/
2fh).

And the crosstalk component Sk from this converter 22
The carrier color signal Sc having the following values is supplied to the C-comb filter 23.

In this case, the carrier frequency of the carrier color signal Sc is fs, while the carrier frequency of the crosstalk component Sk is (fs−
1/2fh) or (fs+1/2fh), the crosstalk component Sk is interleaved with the carrier color signal Sc.

Therefore, in the filter 23, the crosstalk component Sk is removed and only the carrier color signal Sc is extracted.

Then, this extracted carrier color signal Sc is added to the adder circuit 18.
and is added to the luminance signal from the demodulation circuit 17,
Therefore, the original NTSC color video signal is taken out at the terminal 19.

In this case, in the present invention, the above-mentioned frequency conversion signal Ss is generated by the AFC circuit 30.

That is, in this example, the variable frequency oscillation circuit 31
An oscillation signal So with a free-running frequency of 44fh is formed at
As shown in FIG. 7A, the frequency f
h as a rectangular signal Sh, and this signal Sh is supplied to the trapezoidal wave signal forming circuit 33 to generate a signal S as shown in FIG. 7B.
The trapezoidal wave signal St is synchronized with h, and this signal St is supplied to the sampling and hold circuit 34.

Furthermore, the luminance signal from the demodulation circuit 17 is sent to the sync separation circuit 35.
horizontal sync pulse p, as shown in FIG. 7C.
h is taken out, and this pulse Ph is supplied to the reset terminal of the flip-flop circuit 36, and at the same time, the pulse Ph is supplied to the reset terminal of the flip-flop circuit 36.
The signal Sh from 2 is supplied to the differentiating circuit 37, and the signal Sh from FIG.
As shown in FIG. 3, a differential pulse Pc is formed every time the signal Sh rises, and this pulse Pd is supplied to the set terminal of the flip-flop circuit 38 through the normally closed switch circuit 38.

Therefore, from the flip-flop circuit 36, as shown in FIG. 7E, a pulse Pf is obtained which rises every time the pulse Pd rises and falls when the pulse Ph rises.

In this case, the detection signal from the dropout detection circuit 16 is supplied to the switch circuit 38 as its control signal, and the switch circuit 38 is turned on when there is no dropout and turned off when there is a dropout.

Then, the pulse Pf from the flip-flop circuit 36 is supplied to the monostable multivibrator 39, and as shown in FIG. Pulse Pm
is supplied to the sampling hold circuit 34 as a control pulse for sampling, and the signal St is sampled while the pulse Pm is rising.

In this way, in the sampling and hold circuit 34, the rising portion of the trapezoidal wave signal St is sampled by the pulse Pm, and the sampled value is held until the next sampling to a level corresponding to the phase difference between the signal St and the pulse Pm. A DC signal is extracted, and this DC signal is supplied to the variable wave number oscillation circuit 31 as its control signal.

Therefore, in a steady state, the signal St and the pulse Pm are in a synchronized state, and the pulse Pm is synchronized with the horizontal synchronizing pulse Ph.
h is the frequency fh of the horizontal synchronizing pulse Ph and is synchronized therewith, and the signal So, which is a signal before this signal Sh is divided, has a frequency of 44fh and is synchronized with the horizontal synchronizing pulse Ph. It turns out.

In this way, from the AFC circuit 30, a rectangular wave signal S having a frequency of fh is synchronized with the horizontal synchronizing pulse Ph as a reference.
h and an alternating signal So having a frequency of 44fh are extracted.

From these signals Sh and So, an alternating signal Ss for converting the carrier frequencies fa and fb of the carrier color signal Sc to the original carrier wave number 15 is formed.

In other words. The signal So from the AFC circuit 30 is supplied to the frequency converter 41, and the frequency is changed to (fs-1) by the variable frequency oscillation circuit 54 of the APC circuit 50, which will be described later.
An oscillation signal with a frequency of {44fh+(fs-1/
4fh)}=(fs+fa) is taken out, and this signal Sf is supplied to one input contact of the switch circuit 42 and is phase inverted in the inverter 43 to become a signal -Sf. supplied to the other input contact.

Further, the signal Sh from the AFC circuit 30 is supplied to the flip-flop circuit 45 via the phase correction circuit 44 as needed, and is converted into a rectangular wave signal Sr that is inverted every horizontal period as shown in FIG. 6E. Signal Sr is OR circuit 4
6.

Furthermore, the luminance signal from the demodulation circuit 17 is transmitted to the sync separation circuit 4.
This pulse is supplied to the flip-flop circuit 48 and converted into a rectangular wave signal that is inverted every field period, as shown in FIG. supplied to

Therefore, as shown in FIG. 6G, for example, the OR circuit 46 outputs a signal Sw that rises during every other field period Ta and inverts every horizontal period during the remaining every other field period Tb. can get.

This signal Sw is then supplied to the switch circuit 42 as its control signal. For example, when the signal Sw is rising, the switch circuit 42 is switched to the state shown in the figure, and when the signal Sw is falling, it is switched to the state shown in the figure. can be switched to the state of

In this case, the pulse from the pulse generating means 6 is supplied to the flip-flop circuit 48 through the waveform shaping circuit 49, and the output signal of the flip-flop circuit 48 (sixth
The phase in FIG. F) is controlled to be constant with respect to the rotational phase of the heads 1A and 1B.

Therefore, if the output signal of the switch circuit 42 is Ss, the switch circuit 42 is switched to the state shown in the figure during the field period Ta, and the signal Ss is the output signal of the converter 41.
Therefore, as shown in FIG. 6C, during the field period Ta, the frequency of the signal Ss is equal to (fs
+fa).

On the other hand, during the field period Tb, the switch circuit 42
Since it is switched every horizontal period, the switch circuit 42
The signal Sf and the signal -Sf are taken out alternately every horizontal period, but this is a rectangular wave signal Sr that inverts between +1 and -1 every horizontal period (Fig. 6E). in,
This is equivalent to balanced modulation of the signal Sf, and therefore, during the field period Tb, the output signal Ss of the switch circuit 42 is a balanced modulated signal by the signal Sr.

Considering this signal Ss, since this signal is a signal obtained by balanced modulating the signal Sf with the signal Sf, its frequency spectrum is as shown in FIG.
s+fa) is the carrier frequency, and from this, there are sideband components at frequency positions that are odd multiples of 1/2fh.

However, in this case, the frequency of the sideband component of the modulated signal Ss can be expressed as follows.

However, in this case, as will be described later, the sideband component of the modulated signal Ss where m≠0 has no meaning, so
Ignore those sideband components.

Therefore, during the field period Tb, as shown in FIG. 6C, the frequency of the signal Ss is (fs+fb).

Therefore, from the switch circuit 42, the frequency becomes (fs+fa) during the field period Ta, and the frequency becomes (fs+fa) during the field period Ta.
A signal Ss having a frequency (fs+fb) is extracted.

With this signal Ss, the carrier color signal Sc is changed as described above. The frequency is converted to the original carrier frequency fs.

In this case, during the field period Tb, the signal Ss includes a signal component with a frequency of (fs+fb) as well as a signal component with a frequency of (fs+fb).
It also includes the signal component fb±m・fh) (m≠0). Even with this signal component of m≠0, the carrier color signal Sc
is frequency-converted, and the frequency-converted carrier color signal is the original frequency-converted carrier color signal Sc.
You will end up in trouble.

However, in this case, the signal component with m≠0 is a sideband component balanced modulated by the harmonic of the signal Sh, and since the level of the harmonic of the signal Sh is small, the level of the signal component with m≠0 is also small. , the carrier color signal Sc that has not been frequency-converted is distributed for each frequency fh with that frequency as the center, so the carrier color signal that has been frequency-converted by the signal component of m≠0 is the original frequency-converted carrier. Therefore, for these reasons, the signal component of the signal Ss where m≠0 can be ignored, and during the field period Tb, the signal Ss has a frequency of (fs
+fb).

Therefore, the converter 22 obtains the carrier color signal Sc whose frequency has been converted to the original carrier frequency fs.

In this case. An APC circuit 50 is provided to stabilize the reference phase of the carrier color signal Sc. In other words, a fixed oscillation circuit 51 is provided, from which an oscillation signal with a frequency of fs is supplied to the phase comparison circuit 52. Filter 23
The carrier color signal Sc is supplied to a burst gate circuit 53 to extract a burst signal, this burst signal is supplied to a comparator circuit 52, and the phase is compared with the oscillation signal from the oscillation circuit 51, and the comparison output is a variable frequency Oscillation circuit 5
4 as its control signal.

In this way, the reference phase of the carrier color signal Sc is stabilized.

In this manner, according to the present invention, by recording color video signals at high density, track 4A is recorded as shown in FIG.
Even if there is no guard band or a part of the guard band overlaps between 4B and 4B, the color video signal can be reproduced without inter-track crosstalk.

Furthermore, since all the carrier color signals Sc are reproduced, the S/N of the reproduced carrier color signals Sc is good, and a clear color image is reproduced.

Furthermore, during reproduction, in order to convert the carrier frequency of the carrier color signal Sc from fa or fb to fs, generally the carrier frequency f
It requires a signal oscillation circuit to convert a to fs and a signal oscillation circuit to convert carrier frequency fb to fs, which makes the configuration complicated and causes problems such as interference between the two oscillation circuits. However, in the present invention, only one oscillation circuit is required, so the configuration does not become complicated and signal interference does not occur.

Furthermore, since the signal Sr (FIG. 6E) is inverted every horizontal period, it is possible to form it by supplying the horizontal synchronizing pulse Ph to the flip-flop circuit 45, but in such a case, When there is noise in the horizontal synchronizing pulse Ph, the flip-flop circuit 45 malfunctions, making it impossible to obtain the correct signal Sr and, therefore, the correct signal Sw.

However, in the present invention, the signal s from the AFC circuit 30
h to form the signal Sr, thereby obtaining the signal Sw, and even if the horizontal synchronizing pulse ph contains noise, the AFC
Due to the flywheel effect of the circuit 30, the noise does not affect the signal sh, so the correct signal S is always output.
Therefore, the carrier frequency of the carrier color signal Sc can be reliably converted to fs during the field period Tb.

Moreover, in that case, instead of directly using the horizontal synchronizing pulse Ph as the pulse Pm for sampling the signal St, the pulse Pf is obtained from the horizontal synchronizing pulse Ph and the signal Sh, and sampling is performed based on this pulse Pf. Since the pulse Pm is obtained, as shown by the dotted line in FIG. This also ensures the frequency conversion of the carrier color signal Sc, since the operation is not disturbed by its noise or equalization pulses.

Further, when a dropout occurs, the detection signal turns off the switch circuit 38 for the dropout period and the flip-flop circuit 36 is not set, so that the pulse Pf is not formed, and therefore, at the time of this dropout, sampling of the signal St is performed. Since the same frequency of oscillation of the oscillation circuit 31 is not disturbed by the flywheel effect, the frequency conversion of the carrier color signal Sc is performed correctly even if there is a drop-out.

Furthermore, at the time of dropout, the carrier color signal Sc from the converter 22 cannot be obtained, but the comb filter 23
is composed of a delay circuit whose delay time is one horizontal period and a subtraction circuit, so the signal from the delay circuit is used to control the signal from the filter 23 even during the dropout period. is the carrier color signal Sc
is obtained.

Note that in the above description, the carrier frequency of the carrier color signal Sc is f
When converting from a or fb to fs, the frequency of the conversion signal Ss is changed to (fs+
fa) and (fs+fb), the frequency of the carrier color signal Sc is converted by setting the same wave number of this signal Ss as (fs+fa), and the carrier color signal Sc is converted to the switch circuit 42 in the same way as the signal Ss. and inverter 43 and signal S
Similar frequency conversion can be performed by switching and taking out the signal using w.

For example, when reproducing a PAL color video signal,
The signal Sw may be inverted every two horizontal periods in the field period Tb.

Furthermore, the present invention can be applied to the case where a color video signal is reproduced from a magnetic sheet or the like.

[Brief explanation of drawings]

1 to 4 are diagrams for explaining the present invention, FIG. 5 is a system diagram of an example of the present invention, and FIGS. 6 to 8 are diagrams for explaining the same. 22.41 is a frequency converter, 23 is a comb filter, and 30 is an AFC circuit.

Claims (1)

[Claims] 1. When reproducing the carrier chrominance signal and the luminance signal from a recording medium on which the carrier chrominance signal and the luminance signal are recorded, the carrier chrominance signal and the luminance signal having their phases controlled so as to interleave each other in frequency in adjacent tracks, the reproduced luminance signal Supplying the horizontal synchronization pulse obtained from the above to an AFC circuit, extracting a signal synchronized with the horizontal synchronization pulse from the AFC circuit, and controlling the phase of the carrier color signal to return to its original state based on this signal, A reproduction circuit for a carrier color signal, which stops a sampling operation for detecting a phase difference with respect to a horizontal synchronizing pulse in the AFC circuit when a dropout is detected.