JPS6096989A - Chrominance signal regenerating method - Google Patents

Abstract

PURPOSE:To execute regeneration suitable for miniaturization by sampling a low-band conversion chrominance signal by a N-fold clock which is locked to a low-band converted burst phase, and synthesizing the obtained color difference signal data by a n-fold reference clock of the carrier frequency of a chrominance signal to be carried. CONSTITUTION:A regenerative signal which is supplied from a head 1, passes a LPF2 and an ACC circuit 3, goes to a low-band conversion chrominance signal, and is supplied to an A/D converter 18. An A/D convertion clock is sampled by a four-fold clock 4FC which is synchronized to an burst of the low-band conversion chrominance signal in phase. A clock FC is made from the clock 4FC by a timing circuit 24, and the clock FC is converted to two color difference signal data (a) and (b) by a decoder 19 using the clocks FC and 4FC, and a clock 2FC as references. The data (a) and (b) are supplied to an encoder 21 through comb- shape filters 20a and 20b, the carrier signal of the prescribed carrier frequency fSC is outputted through a D/A converter 22 and a BPF23. In such a way, a chrominance signal suitable for making a processing circuit smaller in size and lower in cost in regenerated.

Description

DETAILED DESCRIPTION OF THE INVENTION The field of industrial application Mizumoto f3A relates to a color signal reproducing method in a signal processing circuit of a color video signal recording and reproducing apparatus.

Conventional configuration and its problems Conventionally, in equipment that performs high-density recording of color video signals, such as a rotating head type magnetic recording/reproducing device (VTR), a modulated luminance signal that is FM modulated and a low frequency signal that is converted to a low frequency band. The converted color signal is frequency-multiplexed and recorded. In addition, since there is no guard band between adjacent tracks, a method for removing crosstalk between adjacent tracks is required. For modulated luminance signals, slope azimuth recording is performed, and for converted color signals, adjacent tracks The phase of the color signal of one track (hereinafter referred to as track) is set to 1 for the other track (hereinafter referred to as B track) so that a frequency interleave relationship is established between the two tracks.
It is reversed every underwater cycle (hereinafter referred to as PI method),
A1. The phase of the carrier wave for conversion is softened by 90 degrees in opposite directions on the rack and B track every horizontal period (hereinafter referred to as PS
(This is called a method). The low-frequency converted color signal that has been converted and recorded as described above must be returned to the original carrier color signal at the time of reproduction. The method shown was taken.

In Figure 1, 1 is the F recorded on the magnetic tape during playback.
The mixed wave of the M-modulated luminance signal and the low-frequency conversion color signal is supplied. 2 is the low-pass filter (LPF) for extracting the low-frequency conversion color signal from the mixed wave, and 3 is the input. ACC circuit for adjusting the level of the color signal; 4 a multiplication circuit for returning the carrier frequency fo of the low-frequency converted color signal to the original color subcarrier frequency fsc; Comb filter removing talk pl- (CoMB), 6 is no ζ no 7 amph (
BUFF), 7 is a pantone filter (BPF) that cuts off the upper waveband of the signal output from the multiplier circuit 4 and extracts only the original carrier color signal of the transmission frequency f6G.
).

Frequency conversion of the carrier color signal is performed by the multiplication circuit 4, which converts the frequency of the carrier color signal into a low frequency converted color signal using the low carrier frequency f. This is done by multiplying a signal with a frequency equal to the sum of the color subcarrier frequency f (fBC'+fC' in FIG. 1), but in order to obtain the above signal ft4c'+fc', the following means are used ing. In FIG. 1, synchronization is first performed with one horizontal period separated from the reproduced luminance signal. <From the signal fH, the PLL circuit 14 generates a signal mfc' having a frequency corresponding to m times the low frequency carrier frequency fc (where m is a positive integer), and m fo' is determined whether the reproduction track, A track, or B The low carrier frequency f is obtained by the PI/PSl path 11 which performs frequency division, nine phase inversion, and phase/ft processing based on the signal PG indicating whether the track is a track or the Norms fH. A signal fc' whose frequency and phase have been changed is supplied to one input of the auxiliary multiplier circuit 12. However, the signals f and I have a low carrier frequency f due to a delay in the response of the PLL circuit 14 to jitter that occurs during reproduction. does not match exactly. Therefore, the reference color subcarrier frequency is added to the signal fc', and f8c' +
Even if f, ', the color subcarrier frequency of the reproduced carrier color signal will have jitter. Therefore, the color signal is returned to the original carrier frequency fsc after passing through the bandpass filter 7, and only the color subcarrier is extracted by the burst gate circuit (BG) s, and the output f, c of the reference oscillator (XC○) 1O
// and a phase comparison circuit (PC) 9, and after converting the phase error into a voltage, it is supplied to a voltage controlled oscillator (VXO) 15, and the voltage controlled oscillator 15 generates a reference oscillation output fsc.
/7, by creating an output f8c' with frequencies f8o and i (negative) and a phantom phase error, and supplying the appeal output fsc' to the other input of the auxiliary multiplier circuit 12, the predetermined 4°'+fC' is obtained, and the above fB C'+fC'
and the low-pass converted color signal are multiplied by the multiplier circuit 4 to make the 1st general sending frequency of the carrier color signal after frequency conversion into a jitter-free, 1"L phase locked to the reference oscillation output f, c/7. ing.

In FIG. 2, each circuit 1 to 13 has the same configuration as in FIG.
is phase-compared with fsC', and roof reiltar
FILTER) After converting the phase error to voltage in 1e,
The voltage controlled oscillator 17 generates a signal m f having a frequency m times the low frequency carrier frequency. ' is being made.

In order to return the low frequency converted color signal to a jitter-free carrier color signal of a predetermined carrier frequency as in the two examples above, two multiplier circuits, the conventional multiplier circuit 4 and the auxiliary multiplier circuit 12, are required. Also, as a characteristic of the multiplier circuit, two frequencies f
Multiplying the signals of a and fb, the output is frequency fa+
Since it is the sum of the two signals fb and fa-fb,
In order to obtain a signal of a predetermined frequency, at least one bandpass filter (bandpass filter 7.13 in Figures 1 and 2) is required for each multiplier circuit, which increases the number of circuit components and the circuit area. It becomes. The comb-shaped filter 6 also uses a glass delay line, which has the disadvantages of being expensive and requiring a large circuit area. Furthermore, even if the band-pass filter or comb filter mentioned above is made into a semiconductor or the processing system is digitized and made smaller, a high-speed device is required to process high-frequency signals.
The problem is that power consumption increases.

OBJECTS OF THE INVENTION It is an object of the present invention to provide
It is possible to remove the bandpass filter and perform digital processing at extremely low speeds, and it is also easy to use semiconductors such as comb filters, making it suitable for downsizing and lowering the cost of processing circuits.Color signal reproduction The purpose is to provide a powerful method.

Structure of the Invention The color signal reproducing method of the present invention samples a low frequency converted color signal obtained from a recording medium with an N times clock that is locked to the phase of the low frequency converted burst, and converts the sampled data into two color difference signals. Performs the process of converting it into data, and uses the reference clock n times the carrier frequency of the carrier telegraph system to
A predetermined carrier color signal is obtained by means for synthesizing and outputting two color difference signal data, thereby making it easier to reduce the number of circuit parts and to use semiconductor circuit parts.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

Figure 3 shows how the color signal processing method of the present invention is applied to a rotating head type VTR.
FIG. 2 is a block diagram of an embodiment of the present invention when used in a color signal reproduction processing circuit. In Fig. 3, 1 is a head to which a mixed wave of the FM modulated luminance signal recorded on the magnetic tape and the low frequency converted color signal is supplied during playback, and 2 is a head for separating and extracting the low frequency converted color signal from the mixed wave. low pass filter, 3
1 is an ACC circuit that adjusts the level of the input color signal; 18 is an A/D converter that samples the low-frequency conversion color signal that has passed through the ACC circuit 3 and converts it into digital data; Decoders (DECODE) 20a and 20b that demodulate data into two color difference signal data
are each composed of a random access memory or a soft register, and a comb filter that stores the input data and at the same time reads out the data from one horizontal period before, adds it to the currently input data, and outputs the result. 21 is an encoder that converts the color difference signal data outputted from 20a and 20b into carrier color signal data of a predetermined carrier frequency; 22 is a D/A converter that converts the inputted carrier color signal from D/A to output the carrier color signal; A converter, 23 is a band pass filter, 24
u horizontal synchronizing pulse fH of the reproduced luminance signal,) carrier frequency f of the rack discrimination signal PG and the low frequency conversion color signal. From the clock 4FC, which is four times as large as 4FC, to the clock F, which has the same frequency and phase as the low frequency conversion color subcarrier. a timing circuit that generates 26
is a mono multi-by-break (MM) that delays the pulse fH and generates a pulse at the burst position of the low frequency conversion color signal.
, 26 is a burst game 1 that extracts only bursts of low-frequency conversion color signals, and 27 is a pulse f process (and a PL that creates a continuous lock 4FC from low-frequency conversion bursts of frequency fc).
L circuit 28 is a crystal oscillator.

The color signal reproducing method of this embodiment configured as above will be described below. Here, a clock with four times the low gamut color subcarrier frequency is used as the A/D conversion clock. First, as in the conventional example, the reproduced signal supplied from the head 1 is passed through a low-pass filter 2. The signal passes through the ACC circuit 3 and is supplied to the A/D converter 18 as a level-adjusted low-frequency converted color signal C'. FIG. 4 shows a vector diagram of the above signal C'. As shown in the figure, it is a form in which two color difference signals are quadrature two-phase balanced modulated, and the balanced modulated signals a' and b' with a phase difference of 9000 are obtained. It is peaceful. d' in FIG. 4 indicates the vector of the low frequency conversion burst. Also the 6th
The figure shows the waveforms of signals a', b', c' and burst d', and the timing diagram of each part clock and data.
When the A/D conversion clock is A/D converted using a four times clock 4FC synchronized with the phase of the burst d' of the low frequency conversion color signal, the output data C of the A/D converter 18 is as shown in the figure. The color difference signals a and b and data obtained by inverting their positive and negative signs are alternately and repeatedly output. Therefore, a clock FC having the same frequency and phase as the low-frequency conversion burst d' is created by the tying circuit 24 from the quadrupled clock 4Fc synchronized with the above-mentioned burst phase, and the above-mentioned clock F
C and 4F. The decoder 19 separates the A/D conversion data into two sets of color difference signal data a, -a, and -b based on the three clocks of the clock 2Fo, which is twice as large as the FC, and the timing of the clock 2F. Two sets of data8. By inverting the positive and negative signs of data -a, -b, respectively, two color difference signal data a, b are obtained.
Convert to The color difference signal data is added to the previous data by 1H by the comb filters 20a and 20b, respectively, and is supplied to the encoder 21 as color difference signal data e and f. The encoder 21 receives two color difference signal data e,
Data e, -f obtained by reversing the positive and negative signs of f
is switched and outputted in the order of f, e, -f, -e using a reference clock 4F, and the carrier frequency 'BC of the data outputted from this is % of the clock 4F. Furthermore, since the reference clock 4FsC is output from the crystal excavator 28, the carrier frequency fgo of the carrier color signal data does not include jitter. The signal converted into an analog signal by the D/A converter 22 also contains no jitter. Since the D/A conversion converter contains many secondary harmonics, the harmonics are removed by a bandpass filter 23 to obtain a carrier color signal of a predetermined carrier frequency fBC.

Note that the PLL circuit 27 has an A/D conversion clock 4F.

The low frequency conversion burst d' and the clock F are extracted by the burst gate 26 according to the pulse timing of the mono multi-biflator 25.

The horizontal synchronizing pulse fH is used to keep the frequency relationship between fH and 4Fo constant.

In the above explanation, four times the frequency of the low frequency conversion burst (N=
4) is sampled using the clock and converted into two color difference signal data, which is four times the carrier frequency of the carrier color signal (n=4).
The case where the above two color difference signals are synthesized using a reference clock of It is also possible to obtain a predetermined carrier color signal by combining the above two color difference signals using a reference clock with n times the frequency. For example, in the case of N-8, the data corresponding to C in FIG. 6 is @ , b, -a, -b
Instead of repeating four data, a, a/F+b/
E, b, -a/f2+b/42.

N-N' + bsin (9007X 360 0)),
However, N'=o−N integer) is repeated. ” - The combination data of a and b as described can be obtained by multiplying one data C and the data C-1 one time before it by a constant repetition constant l, J, or l, and then adding them. A small file is created that combines the data of a and b, and can be entered as follows, for example.

If the sampling clock is sampled at N times the frequency of the low-frequency conversion burst by conversion as shown in the margin below,
Generally, since it is calculated from sampling data C and sampling data C one clock before, the data b to data a map ζ is mixed with data from data a to data b (hereinafter referred to as cross h). To prevent this, it is necessary to set the multiple N sufficiently large. However, in the case of N=4, as is clear from the above description, it is possible only by inverting the sign of the data, and no crosstalk occurs. In addition, when sampling a certain signal, according to the sampling theorem, it is necessary to sample at a rate of at least twice the signal frequency, and the maximum frequency after passing through the low-pass filter 2 in Figure 3 is in the low frequency range. It is twice the frequency of the conversion burst, and the sampling clock needs to be four times or more the frequency fC of the low-frequency conversion burst. In addition, when converting two color difference signal data into a predetermined carrier color signal, the operation is almost the reverse of the operation when converting the low frequency conversion color signal to a color difference signal by sampling it at N times the clock frequency of the low frequency conversion burst. , for example, 3 of the carrier frequency
When using double (n=3) reference clock, esino°
+ fsin900=f n-n' (general formula esin (00+ -)+fs+n (9
0°+n-n').

Three pieces of data (n n n'=o-n integer) are calculated and output repeatedly. In this case, as in the case of converting the low frequency conversion color signal into two color difference signal data, if n=4, then e5ino O+ fsin900= 1esin9o
°+ fsinl 800= eesin180°+7
sin270°; the esin2700+ fsin36
The four data of 00=-e are repeated, and the carrier color signal data can be synthesized only by inverting the positive and negative signs of the two color difference signals and switching and outputting each data.

Effects of the Invention As is clear from the above explanation, according to the present invention, the frequency conversion is performed by first digitally demodulating the low-frequency conversion color signal and then digitally modulating it, so that the conventional multiplication circuit can It has the effect of removing the band-pass filter that would be required when performing digital processing, and it also eliminates the need for high-speed digital processing to digitally process low-pass converted color signals or demodulated color difference signals in a relatively low frequency range. The effect is that it can be digitized very easily. Furthermore, when sampling the low-pass conversion color signal with a clock that is four times the frequency of the low-pass conversion burst, the sign of the sampled data is inverted even though the clock frequency is the minimum allowed by the sampling theorem. Data sampling clock % frequency phase is 180 respectively
° Two color difference signals can be separated using extremely simple hardware that further samples with different clocks, the effect of reducing crosstalk between color difference signals is achieved, and the two color difference signal data are converted to predetermined carrier color signal data. Even in cases where the reference clock is set to four times the carrier frequency of the carrier electric signal, the signs of the two color difference signals can be reversed, and the operation can be performed simply by switching and outputting the respective data, which can be done using simple hardware. There are effects that can be achieved with

Since the two low-frequency color difference signals are passed through the comb-shaped filter separately, it can be easily replaced with an extremely low-speed semiconductor memory, and the circuit can be made smaller.

[Brief explanation of drawings]

1 and 2 are block diagrams for explaining a conventional color signal reproduction method, and FIG. 3 is a block diagram of an embodiment of a color signal reproduction processing circuit using the color signal reproduction method of the present invention. FIG. 4 is a vector diagram of low-pass conversion color No. 48, and FIG. 6 is a timing chart showing waveforms and data output states of each part in FIG. 3. 1...Head, 2...Low pass filter, 3...ACC circuit, 18.../D converter,
19...Decoder, 20a, 20b...Comb filter, 21...Encoder, 22...
... D/A converter, 23 ... Band pass filter, 24 ... Timing circuit, 25 ... Mono multi-by-break, 26 ... D/A converter, 2
7... Voltage controlled oscillator, 28... Crystal oscillator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 4
Figure (-Yml l-axis

Claims (1)

[Claims] (1) The low frequency conversion color signal obtained from the recording medium is sampled with an N times (N is a positive integer) clock that is locked to the phase of the low frequency conversion burst, and the sampling data is divided into two. The two color difference signal data are synthesized using a reference clock that is n times the carrier frequency of the carrier color signal (where n is a positive integer) and outputted. A color signal reproduction method characterized by obtaining a color signal. (2) A/D as a sampling method for low-frequency conversion color signals
Using a converter, the digital data is converted into two color difference signal data, and the two color difference signal data are synthesized using a reference clock that is n times the 11 carrier frequency of the digital data and then transmitted. 2. The color signal reproducing method according to claim 1, wherein a predetermined carrier color signal is obtained by D/A converting the carrier color signal data. (3) A quadrupled clock locked to the burst of the low-pass converted color signal is used as the sampling clock for the low-pass converted color signal, and the positive/negative sign of the sampling data is inverted at twice the period of the above sampling clock, and the above Claim 1, characterized in that the inverted data is further converted into two color difference signals by means of sampling each with two clocks having a cycle twice that of the sampling clock and a phase difference of 1800. Color signal reproduction method. (4) Using a clock four times faster than that of the carrier color signal as a reference clock, print two color difference signal data and data obtained by inverting the positive and negative signs of the above two color difference signal data. 2. The color signal reproducing method according to claim 1, wherein the carrier color number data of a predetermined carrier frequency is erased by switching with a clock. (6) A color signal reproducing method according to claim 1, characterized in that the low-pass conversion color signal is converted into two digital color difference signal data and then passed through a digital comb filter.