JPS5927146B2 - Signal processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a VTR for high-density recording and reproduction, and more specifically, an object of the present invention is to provide a method that can perform jitter correction without being affected by interference reproduction signals from adjacent tracks. do.

Although it has been known that there are recording and reproducing methods that utilize azimuth loss, there has been a particular desire recently to develop a VTR that can perform long-time recording, that is, high-density recording and reproducing.

In order to achieve high density, narrower tracks, lower relative speeds, and lower tape speeds are used. Tracks are lined up without gaps on the magnetic tape for recording and playback. Each track has an azimuth angle, and each track has its own magnetization direction. The commonly used azimuth recording method is to attenuate reproduction interference signals from adjacent tracks during reproduction until they can be ignored due to azimuth loss due to the azimuth angle. However, a serious problem arises here. In other words, the azimuth loss is related to the recording wavelength, and the larger the recording wavelength, the smaller the azimuth loss. Therefore, the low frequency converted color signal (chroma signal)
Since the loss is small and the interference signal from adjacent tracks is large, normal processing cannot eliminate this. Therefore, the following method is used. In other words, the spectrum of the chroma signal is recorded with a frequency difference of -2fH (fH is the horizontal synchronization frequency) for each track, and during playback, a comb-shaped filter for each fH is used to reproduce the adjacent chroma signal (- There is a method to remove the difference in spectrum by 2fH. Specifically, this method consists of 2
One is considered. The first method is to change the phase of the chroma signal for each horizontal synchronization by 1800 degrees every horizontal synchronization period in order to vary the blue fH frequency, and the second method is to record the entire chroma signal so that it differs by the blue fH frequency. It's a method. The spectrum will be explained with reference to FIG. 1. FIG. 1A is a chroma signal spectrum, B is a recorded low frequency converted chroma signal spectrum, fo is a subcarrier frequency (3.579454 MH2 in NTSO), and fc is a low frequency converted subcarrier frequency. Further, D indicates the recorded low frequency converted chroma signal spectrum, and fH indicates the horizontal synchronization frequency. A is a signal spectrum when modulated as is well known, and is distributed for each fH with fo as the center. The first method described above is to create B from A, that is, to invert the phase every horizontal synchronization. Figure 2 is the first
The waveform obtained by the above method is shown, and the phase of φ is inverted every tH (one horizontal synchronization period). The dotted line is the waveform without inversion.

φ1 has an amplitude of 2 compared to the amplitude 1 of φ, and is a waveform that exists every horizontal synchronization period, and φ2 is a continuous wave with an amplitude of 1. As is clear from the figure, (IF2φ1−φ2
is required. Considering that φ1 is a rectangular wave modulated by 100 (fl), it is expressed as φ1=1nωt.
f(p) is a rectangular wave represented by f(p) in FIG. f(
As is well known, when expressed as a Fourier series, p) is expressed as f(p!壬-》, f≠correctionSin(2n+1)Pt).

On the other hand, φ2 is as shown in the figure.

From the above formula.

Here, the focus is on FO, but if the frequency is converted appropriately, the result will be as shown in FIG. 1B. Next, the second method, that is, v★! from A in Figure 1! ? :゛ et al; 2 liri: 畢; The frequency of the middle phase sum and the difference is obtained, and the difference is D.
It has become a spectrum of

As described above, B or D can be obtained from A in FIG. 1 by two methods. And both B and D are against Fc:;;::heavy;″l′hai?
2. Since the frequencies can be different, there are tracks recorded on magnetic tape using the above method and F tracks recorded on magnetic tape without any processing.
If tracks that record simply low-frequency converted signals centered on C are arranged alternately, even if a signal is mixed in from an adjacent track during playback, the frequency will be different by FH/2, so it will not be mixed with the signal to be played back. This means that the mixed signal can be distinguished from the mixed signal, and the mixed signal can be removed.

FIGS. 3 and 4 show block diagrams for recording based on the above-mentioned principle. In the block diagram, the luminance signal system is omitted and only the chroma system is shown. Components with the same numbers in FIGS. 3 and 4 have the same functions. 1 is an input terminal, 2 is a band filter, 3 is a frequency conversion circuit, 4 is a phase inversion switching circuit, 5 is a recording amplifier, 6 is a magnetic head, 7 is a fixed oscillator, 8 is a switching input terminal, 9
1 shows a switching circuit, and 10 and 11 show fixed oscillators, respectively.

3 is a block diagram using the method of creating B from A in FIG. 1, and FIG. 4 is a block diagram using the method of creating D from A in FIG. 1. To explain with reference to FIG. 3, a video signal input to a terminal 1 is filtered by a bandpass filter 2 to extract only a chroma signal, and then input to a frequency conversion circuit 3.
The frequency of the fixed oscillator 7 is FO+Fc (for example, 4.34 MHz) in FIG. The signal from the fixed oscillator 7 enters the frequency conversion circuit 3 and becomes a low frequency converted chroma signal from FO+Fc-FO-Fc to Fc. This signal enters a phase inversion switching circuit 4, and the phase is inverted or not in response to a switching signal from an input terminal 8. Based on the above-mentioned principle, when one field of a television signal is recorded on one track, the phase is inverted or not inverted every horizontal synchronization period for each field. In other words, the switching signal to the input terminal 8 has a waveform, as shown in the graph shown in FIG. All you have to do is enter. In this way, at the output of the phase inversion switching circuit 4, a signal having the spectrum shown in FIG. The signal is amplified by an amplifier 5 and recorded on a magnetic tape by a magnetic head 6. Although only one magnetic head 6 is shown in the figure, in the case of azimuth recording, it is assumed that a two-head helical scan type VTR is used, so there are actually two heads. FIG. 3 (The phase inversion switching circuit 4 is located after the frequency conversion circuit 3,
3. On the other hand, in order to obtain A to D in FIG. 1, the NfH frequency of the continuous wave for frequency conversion must be made different for each field in the frequency conversion circuit 3 in FIG. 4. For example, FIG. 1D is obtained. For this purpose, the frequency difference between the fixed oscillators 10 and 11 may be set to -2fH. Then, the switching circuit 9 can switch the signal given to the frequency conversion circuit 3 to the fixed oscillators 10 and 11 for each field. The switching signal entering the input terminal 12 may have the waveform shown in FIG. 4b. During reproduction, the circuit shown in FIGS. 5 and 6 performs reproduction.

In addition, in FIGS. 5 and 6, the same numbers have the same functions. Also, only the chroma system is shown, and the luminance signal system is omitted. Also, the commonly used head amplifier is omitted. 2 magnetic heads 1
The signal obtained from 3 is amplified by a head amplifier (not shown) until it can be processed by the circuit, and then passed through a low-pass filter 14.
shall be given to

Figure 5 is a playback block diagram for recording in Figure 3, and Figure 6.
The figure is a reproduction block diagram for the case where recording is performed in accordance with FIG. 4, and the explanation will be given first with reference to FIG. Only the low frequency of the signal applied to the low pass filter 14 is extracted, and a reproduced chroma signal that has been low frequency converted is obtained. This signal is returned to the original chroma signal (3.58 MHz) in the frequency conversion circuit 15. 16 is the same as 14 in FIG. 3, and is a phase inversion switching circuit.

Here, switching is performed using the same signal as the waveform shown in FIG. 3b, as in the case of recording. The signal then enters a comb-shaped filter consisting of one horizontal synchronization time delay element 17 and an adder 18. The signal that has passed through the comb filter is obtained at the output terminal 19. On the other hand, from the continuous wave entering the frequency conversion circuit 15, only a burst signal is extracted from the output of the phase inversion switching circuit 16 by the burst gate circuit 20, and the burst signal is entered into the phase comparator 21. In the phase comparator 21, a fixed oscillator 22
The output from the burst signal is also input, and the phase of this signal and the burst signal is compared. A voltage corresponding to the phase difference between both signals is then obtained. This voltage enters a low-pass filter 23 as a loop filter, controls the oscillation frequency of a variable oscillator 24, and reaches a frequency conversion circuit 25. The output of the fixed oscillator 22 comes here, and the frequency of the sum of both is obtained. This signal is used as a continuous wave for frequency conversion. The loop is now complete and jitter correction is performed. In other words, the reproduced signal usually has jitter and has time axis fluctuations. For this reason, normal color demodulation is not performed on the phase-modulated chroma signal. Therefore, jitter correction is performed using the loop described above. That is, let the reproduced signal be Fc+Δf, and Δf
When is a jitter component, create a continuous wave that is phase-synchronized with this Δf, and take the frequency difference between the frequency FO + Fc + Δf and the input signal.A signal that is phase-synchronized with the fixed oscillator 22 called FO is obtained, and Δf is corrected. be able to. When the jitter-corrected signal is passed through the comb filters 17 and 18, interference signals from adjacent tracks are removed, and an output is obtained at the output terminal 19. Also the 6th
In the figure, the phase inversion switching circuit 16 is not provided, but instead an input terminal 26 is provided, and a switching signal having the waveform shown in FIG. 4B is applied to the terminal 26, as in the case of recording. If a variable capacitance element (diode) or the like is used as the variable element, the bias voltage thereof may be shifted.

As a result, the continuous waves entering the frequency conversion circuit 15H can differ by one frequency.

Here, we will once again discuss the effect of removing interference from adjacent tracks from a spectrum perspective. Figure 7 is Figure 1A
In the case where B is obtained from and recorded, that is, the vector diagram for the reproduction method of the block diagram in Figure 5, Figure 8 is obtained and recorded by obtaining D from Figure 1, and reproduced with the block diagram in Figure 6. It is a figure showing the spectrum of time. First, explanation will be given starting from FIG. The reproduced signal is generally as shown by a. The solid and dotted lines show the difference between the main signal and the interfering signal.
If we now consider the solid line to be the main signal, we can obtain the main signal C by passing it through a comb-shaped filter having characteristics such as b. In the next field, the dotted line can be considered the main signal. This main signal is a field that undergoes phase inversion during recording, and when the same phase inversion is performed during reproduction, the dotted line and solid line in the spectrum are interchanged as shown in d. By passing this signal through a comb-shaped filter having characteristics such as e, only a dotted line such as f can be extracted. Next, FIG. 8 will be described. In this case as well, the reproduced signals include the main signal and the interference signal from the adjacent track, as shown in A and b. Now, if we consider the solid line to be the main signal, then if we perform frequency conversion using a regular continuous wave (FO+Fc) and pass it through a comb-shaped filter with characteristics like d, we can obtain only the solid line like f. On the other hand, when reproducing the next field, the dotted line becomes the main signal. At this time, a signal enters the input terminal 26 in FIG. 6, and the continuous wave entering the frequency conversion circuit 15 is (FO+Fc
After frequency conversion, the dotted line becomes Fc, as shown in FIG. 8c. By passing this through a comb-shaped filter with characteristics such as e, it is possible to obtain only the signal indicated by the dotted line 9. As described above, signals of adjacent tracks can be removed by either of the two methods. However, a big problem arises here. In other words, D
This is the occurrence of G and DP. FIG. 9 is a diagram showing the pattern of a magnetic track, in which heads run in the direction of the arrow to form a magnetic track.

As explained earlier, since the FH/2 frequency is different for each track, looking at the phase of the signal for each horizontal synchronization, the chroma signal has a -offset, so it is 0.1
80), 0, 180), gin゛30τ-nigin゛: ; Power?
÷: In order to tighten and invert the phase every horizontal synchronization period, +++++++... is obtained.

Since the next track will not be reversed again, +1 + - +
One...... Now, let us consider the time when the track in the middle of Figure 9 is to be played back. At this time, due to mechanical precision, head mounting precision, expansion and contraction of the magnetic tape, etc., it is highly unlikely that the head will follow the same trajectory during playback as during recording. Therefore, signals of adjacent tracks are also reproduced. As mentioned at the beginning, the luminance signal is 3
~5MHz0) FM wave, this signal is not reproduced from adjacent tracks due to azimuth loss and does not cause interference. However, the low frequency converted chroma signal has a small azimuth loss, so it causes interference. The chroma signal of this adjacent track is generally the signal to be reproduced, that is, the 9th track.
There is a phase shift with respect to the signal on the middle track in the figure. This phase shift is determined by mechanical precision, phase difference due to azimuth angle, and D
This is caused by alignment accuracy, uneven head rotation during recording, etc., and there is no phase shift in the recorded signal, but it is assumed that there is a phase shift Q during reproduction due to the above-mentioned causes. Since the signals of the adjacent tracks are processed tracks, they are not inverted every horizontal synchronization period. This situation is shown in FIG. A is a diagram showing reproduction signals as vectors for each horizontal synchronization, S is a main signal to be reproduced, and N is an interference signal reproduced from an adjacent track. It is assumed that N has a phase shift Q with respect to S. In the next horizontal synchronization period, S
is reversed by 180, resulting in -S. Since S is inverted every horizontal synchronization period in this way, the composite vector for reproduction is S+N. ．． N-S. ．． It becomes S+N. This S+
NlN-S indicates that the phase varies with respect to S every horizontal synchronization period. Since this signal is phase-compared with the output of the fixed oscillator in the phase comparator, the phase comparison signal swings +-+1 with respect to the reference level as shown in C. When a variable oscillator is controlled with this voltage, the frequency changes with the voltage, and as a result, the phase changes.
Since the phase changes as an integral value of frequency change, it changes in an integrated form like d. If there is such a large phase variation with respect to the reference, the phase of the variable oscillator will not follow immediately but will change with a delay. If this signal is frequency-converted and jitter corrected, the jitter-corrected signal will also have a phase change. That is, if the phase changes as shown in d from the beginning to the end of one horizontal synchronization, the regenerated synthesis vector will also change by a certain angle from the beginning to the end of the horizontal synchronization, as shown in e. In the next horizontal synchronization period, the direction is reversed as shown by d, so the reproduction vector also changes by α degrees in the opposite direction. In this way, when the phase changes during the horizontal synchronization period and the direction of the change changes in the opposite direction every horizontal synchronization period, the problem is what happens to the signal that passes through the next tangent filter. The comb filter consists of one horizontal synchronous time delay element and a subtractor. In other words, the delayed signals are inverted at 180 and added together. A delayed and inverted vector diagram is shown in f. Therefore, e+f is the signal after passing through the comb filter. FIG. 11 shows a composite vector diagram for Ma. In this figure, the inversion at each horizontal synchronization is stopped and only the ma is focused. Each symbol represents a vector, and α is the phase variation angle. In FIG. 11, the signal passing through the comb filter is 2 ma at the beginning of horizontal synchronization, and P1+P2 at the end of 1◆-←◆.

Here, during the horizontal synchronization period, Arg"F-Arg. (p?+
It can be seen that Dp of d) is generated and DG of (1-+)×100% is generated.

Even in experiments, there are cases where this value far exceeds the allowable value. Therefore, the present invention provides a new method for preventing the occurrence of such DG-DP.

FIG. 12 shows an example thereof. FIG. 12 is a partial block diagram of chroma processing on the reproduction side, and the rest is the same as FIGS. 5 and 6 described above. A reproduced chroma signal is applied to the human input terminal 27. This signal is transmitted to the frequency conversion circuit 28
The frequency is converted together with the output of the fixed oscillator (3.58 MHz) 29, and the reproduced signal (767KIIz) is converted into a sum signal of 4.34 MHz. A burst gate circuit 30 performs a burst gate on this converted signal to extract only the burst signal and input it into a phase comparator circuit 31 . The error voltage output of the phase comparison circuit 31 controls the variable oscillator 32 to change its oscillation frequency. Then, this output is frequency-converted together with the signal from the fixed oscillator 29 in a frequency conversion circuit 33 to obtain a continuous wave of 4.34 MHz. This continuous wave is guided to a phase comparator circuit 31. This loop makes it possible to obtain a continuous wave phase-synchronized with the burst of the reproduced signal at the output of the frequency conversion circuit 33. However, DG-D
As mentioned in the explanation of the reason for the occurrence of P, since the reproduced burst signal itself also includes the burst signal of the adjacent track, the phase of the output of the frequency conversion circuit 33 is as shown in the waveform shown in FIG. 10d. has a phase fluctuation within the horizontal synchronization period. Therefore, if this continuous wave is reversely phase modulated with the signal d, the phase fluctuation of the continuous wave can be suppressed. For this purpose, an integrating circuit 34 that integrates the phase error voltage of the phase comparator circuit 31 is provided.
is provided, and the phase modulator 35 is operated by this signal.
The direction of phase variation at this time depends on the type of phase modulator 35, but it must be modulated in the opposite direction to d. In this way, since the phase modulator 35 receives phase fluctuations in the opposite direction, the phase fluctuations in the output of the phase modulator 35 are canceled, and the output does not have phase fluctuations caused by signals from adjacent tracks, so that the horizontal synchronization period No phase fluctuation occurs within the range. Using this signal, when the frequency conversion circuit 36 performs frequency conversion on the reproduced chroma signal from the input terminal 27, the phase fluctuation within the horizontal synchronization period as shown in Fig. 10e disappears, and therefore DG-DP also occurs. It becomes impossible.

The output of the frequency conversion circuit 36 is one horizontal time delay element 37.
and a subtracter 38, which removes interference signals of adjacent tracks contained in the reproduced chroma signal,
It leads to the output terminal 39. Note that the jitter correction by the variable oscillator 32 is to correct relatively low frequencies among the frequency components of the VTR jitter, and in the actual configuration, an integrating circuit corresponding to the integrating circuit 34 is provided on the input side of the variable oscillator 32. (not shown), which is constituted by a circuit whose time constant is sufficiently larger than that of the integrating circuit 34.

On the other hand, the purpose of the integrator circuit 34 is, as mentioned earlier, when using the burst signal inverted every horizontal synchronization for jitter correction, since the phase change changes with the integral value of the frequency change.
Since the correction is performed by changing the phase in the opposite direction to the gradual change within one horizontal period, the time constant is small. For this reason, even if the output signal of the phase comparator 31 [Fig. 10 d] is used for further inverse correction, the frequency components to be corrected are different, so that each initial correction cannot be achieved. be able to. As described above, according to the present invention, it is possible to perform normal jitter correction without disturbing the jitter correction process due to signals of adjacent tracks.

In addition, in FIG. 2, of the two methods of recording the chroma signal mentioned above, the first method, that is, the method of inverting the phase, is assumed, and the signal input to the input terminal 27 has already been recorded at the time of reproduction. The signal is obtained after performing phase inversion processing.
In the second method, the bias of the variable oscillator is changed in the same way as in FIG.
If the integrating circuit 34 and phase modulator 35 are provided as shown in the figure,
It is possible to implement. 6 engineering I2-:=growth←:? Yes, but is it obvious from the principle? It is clear that -1fH (n is an integer) is sufficient.

Also, although it is stated that the luminance signal should be FM modulated,
In particular, not only FM modulation but also angle modulation may be used.

[Brief explanation of the drawing]

Figure 1 is a spectrum for explaining two methods of removing interference from adjacent tracks in azimuth loss, Figure 2 is a signal waveform diagram used to explain Figure 1, and Figure 3 is a recording system for the first method. Figure 4 is a block diagram of the recording system of the second method, Figures 5 and 6 are block diagrams of the playback system in each method, and Figures 7 and 8 are playback diagrams in each method. Fig. 9 is a tape pattern diagram to explain the drawbacks of the above two methods, Fig. 10 is a vector diagram of the reproduced signal, and Fig. 11 is a vector diagram showing the occurrence of DG-DP. , FIG. 12 is a block diagram showing an embodiment of the reproduction system in the method of the present invention. 27... Input terminal, 28, 33, 36...
...Frequency conversion circuit, 29...Fixed oscillator, 3
0... Burst gate circuit, 31...
Phase comparison circuit, 32... Variable oscillator, 34...
...Integrator circuit, 35...Phase modulator, 37
1 horizontal time delay element, 38 subtractor, 39 output terminal.

Claims (1)

[Claims] 1 The chroma signal spectrum frequency-converted to the lower frequency side is divided into (2n-1/2) f_H (n is an integer) for each magnetic track.
f_H is the horizontal synchronization frequency) and record it differently,
The luminance signal is recorded as an angle-modulated signal on the high frequency side, and during playback, the phase of the continuous wave created by controlling the frequency and phase using the burst signal in the reproduced chroma signal is detected by the phase comparator during the phase control described above. A signal processing method characterized in that a signal obtained by integrating an error signal is inverted and phase modulated, and the phase modulated continuous wave is used to perform time axis correction of a chroma signal.