JPH038634B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention 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 Conventional rotating head type magnetic recording and reproducing device (VTR)
Devices that perform high-density recording of color video signals, such as FM-modulated luminance signals and low-frequency converted color signals, are frequency-multiplexed and recorded. Also, since there is no guard band between adjacent tracks, a method is required to eliminate crosstalk between adjacent tracks.
For the modulated luminance signal, tilt azimuth recording is performed, and for the converted color signal, one track (hereinafter referred to as the A track) is recorded against the other track (hereinafter referred to as the A track) so that a frequency interleave relationship is established between adjacent tracks. The phase of the color signal of the B track (hereinafter referred to as B track) is inverted every horizontal period (hereinafter referred to as PI method), and the phase of the carrier wave for conversion is shifted in the opposite direction by 90 degrees every horizontal period in A track and B track. (hereinafter referred to as the PS method). The low-frequency converted color signal converted and recorded as described above must be returned to the original carrier color signal during playback. Conventionally, the color signal playback method shown in Figure 1 or Figure 2 has been used. A method was taken. In Figure 1, 1 is a head to which a mixed wave of an FM modulated luminance signal recorded on a magnetic tape and a 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 liquid. Low pass filter (LPF), 3 adjusts the level of the input color signal
ACC circuit; 4 is a subtraction circuit for returning the carrier frequency _c of the low frequency converted color signal to the original color subcarrier frequency _sc ;
5 is a comb filter (COMB) that removes crosstalk between adjacent tracks due to the frequency interleaving relationship, 6 is a buffer amplifier (BUFF), and 7 is a filter that cuts off the upper sideband of the signal output from the subtraction circuit 4. , is a bandpass filter (BPF) that extracts only the original carrier color signal of the carrier frequency _sc . Frequency conversion of the carrier color signal is performed by subtracting circuit 4, which converts the low frequency carrier frequency _c and the color subcarrier frequency _sc into the low frequency converted color signal.
This is done by multiplying the signal with the frequency of the sum of ( _sc ′+ _c ′ in Figure 1), but the above signal _sc ′+
In order to obtain _c ′, the following method is used. In Figure 1, first, from the pulse _H synchronized with one horizontal period separated from the reproduced luminance signal.
A signal having a frequency equivalent to m times the low frequency carrier frequency _c (where m is a positive integer) is generated by the PLL circuit 14.
m _c ' is generated, and m _c ' is lowered by the PI/PS circuit 11 which performs frequency division, phase inversion, or phase shift processing based on the signal PG and pulse _H indicating whether it is a reproduction track, A track, or B track. A signal _c ' whose frequency and phase are locked to the range carrier frequency _c is supplied to one input of the auxiliary multiplier circuit 12. However, the signal _c ' does not exactly match the low carrier frequency _c due to a delay in the response of the PLL circuit 14 to jitter that occurs during reproduction. Therefore, the reference color subcarrier frequency is added to the signal _c ′.
Even if _sc '+ _c ', the color subcarrier frequency of the reproduced carrier color signal will have jitter. Therefore, only the color subcarrier is extracted from the color signal returned to the original carrier frequency _sc by the burst gate circuit (BG) 8 after passing through the bandpass filter 7, and the phase is compared with the output _sc '' of the reference oscillator (XCO) 10. Circuit (PC)
After comparing the phases in step 9 and converting the phase error to voltage,
The voltage controlled oscillator (VXO) 15 generates an output _sc ' having a phase error opposite to the frequency _sc with respect to the reference oscillation output _sc '', and the output _sc ' is sent to the auxiliary multiplier circuit 12. By supplying the other input, a predetermined _sc ′ + _c ′ is obtained, and by multiplying the above _sc ′ + _c ′ and the low-frequency converted color signal by the subtracting circuit 4, the carrier color signal after frequency conversion is obtained. The carrier frequency is jitter-free and phase-locked to the reference oscillation output _sc ''. In FIG. 2, each circuit ₁ to 13 _has the same configuration as in _FIG .
Compare the phase _{of sc} with _sc ′ and apply a loop filter (LOOP
After converting the phase error into voltage with FILTER) 16,
A voltage controlled oscillator 17 generates a signal m _c ' having a frequency m times the low frequency carrier frequency. As in the above two examples, in order to return the low frequency converted color signal to a carrier color signal of a predetermined carrier frequency without jitter, the conventional subtracter circuit 4 and the auxiliary multiplier circuit 12 are required.
Two subtraction circuits are required, and as a characteristic of the subtraction circuit, when two signals with frequencies _a and _b are multiplied, the output is the sum of the two signals with frequencies _a + _b and _a - _b . Therefore, in order to obtain a signal of a predetermined frequency, at least one bandpass filter (bandpass filters 7 and 13 in FIGS. 1 and 2) is required for each subtraction circuit, and the number of circuit components is
This causes the circuit area to increase. The comb filter 5 also uses a glass delay line, which has the disadvantages of being expensive and requiring a large circuit area. Furthermore, even if the above-mentioned bandpass filters and comb filters are made into semiconductors or the processing system is digitized and miniaturized, high-speed devices are required to process high-frequency signals, which causes problems such as increased power consumption. It's summery. Purpose of the Invention The purpose of the present invention is to eliminate the bandpass filter that conventionally occupied a large circuit area;
Another object of the present invention is to provide a color signal reproducing method that allows digital processing to be performed at low speed, and that is also easy to use in semiconductors such as comb filters, and is suitable for downsizing and lowering the cost of processing circuits. 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 sampling data into two color difference signals. The above two color difference signal data are sampled again using a reference clock that is n times the carrier frequency of the carrier color signal, and each of the quadrature phase carriers of the carrier color signal is sampled using the reference clock that is n times the carrier frequency of the carrier color signal. A predetermined carrier color signal is obtained by an output means that multiplies each of the color difference signals by n circulating digital data strings corresponding to digital values at the time of the color difference signal and then adds and outputs the result. This makes it easier to reduce the number of circuit parts and to convert them into semiconductors. DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram of an embodiment in which the color signal processing method of the present invention is applied to a color signal reproduction processing circuit of a rotary head type VTR. 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 liquid. 3 is an ACC circuit that adjusts the level of the input color signal; 18 is an A/D converter that samples the low-pass converted color signal that has passed through the ACC circuit 3 and converts it into digital data; 19 is the A/D converter that samples the low-pass conversion color signal that has passed through the ACC circuit 3; The decoders (DECODE) 20a and 20b, which demodulate D-converted data into two color difference signal data, each consist of a random access memory or a shift register, and store the input data and simultaneously store the data from one horizontal period before. A comb filter that reads out the data, adds it to the currently input data, and outputs the result, 21
20 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, and 22 is a D/A that converts the input carrier color signal into a D/A and outputs the carrier color signal. Converter, 23 is a bandpass filter, 24 is a horizontal synchronizing pulse _H of the reproduced luminance signal, and a track discrimination signal PG.
and the same frequency as the low-pass conversion color subcarrier from a clock 4F _c multiplied by 4 times the carrier frequency _c of the low-pass conversion color signal,
A timing circuit that generates a clock F _c of the same phase, 25 a mono multivibrator (MM) that delays pulse _H and generates a pulse at the burst position of the low frequency conversion color signal, and 26 only the burst of the low frequency conversion color signal. 27 is a PLL circuit that creates a continuous clock 4F _c from the pulse _H and the low frequency conversion burst of frequency _c ; 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 passes through the low-pass filter 2 and the ACC circuit 3, and is supplied to the A/D converter 18 as a level-adjusted low-frequency conversion color signal c'. . Figure 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 balanced modulated signals a' and b with a phase difference of 90° are generated. ′. Figure 4
d′ indicates the vector of the low frequency conversion burst. Figure 5 also shows signals a', b', c' and burst
The waveform of d' and the timing diagram of various clocks and data are shown. The A/D conversion clock was A/D converted using a 4x clock _4Fc synchronized with the phase of the burst d' of the low frequency conversion color signal. In this case, the output data c of the A/D converter 18 is output as the respective color difference signals a and b and data obtained by inverting the positive and negative signs of the respective color difference signals a and b are alternately repeated as shown in the figure. Therefore, the timing circuit 24 generates a low-frequency conversion burst from the quadrupled clock _4Fc synchronized with the burst phase.
Create a clock F _c with the same frequency and phase at d′,
The above clock F _c and 4F _c and clock 2 which is twice as large as F _c
Based on the three clocks of F _c , the decoder 19
At _the same time, the A/D conversion data c is separated into two sets of color difference signal data a, -a and b, -b. The signals are converted into two color difference signal data a and b by inverting the signs of each. The color difference signal data is added to the previous data by 1H by comb filters 20a and 20b, respectively, and is supplied to the encoder 21 as color difference signal data e and f. The encoder 21 outputs data -e and -f obtained by inverting the positive and negative signs of the two color difference signal data e and f, respectively, by switching them in the order of f, e, -f, and -e using the reference clock 4F _sc . Carrier frequency _sc of output data
is 1/4 of clock 4F _sc . Further, since the reference clock 4F _sc is output from the crystal oscillator 28, the carrier frequency _sc of the carrier color signal data does not include jitter, and the carrier color signal data is converted into an analog signal by the D/A converter 22 using the clock 4F _sc . The converted signal also contains no jitter. Since the carrier color signal after passing through the D/A converter 22 contains many harmonics due to digital processing, the harmonics are removed by a bandpass filter 23 to obtain a carrier color signal with a predetermined carrier frequency _sc . Note that the PLL circuit 27 is the A/D conversion clock _4Fc.
It is a mono multivibrator 25.
The pulse timing operates so that the phase of the low-frequency conversion burst d' taken out by the burst gate 26 and the clock F _c becomes the same, and the horizontal synchronizing pulse _H keeps the frequency relationship between _H and 4F _c constant. This is what I did. In the above explanation, the frequency of the low frequency conversion burst is 4.
An explanation will be given of the case where sampling is performed using a clock that is twice as high (N = 4) and converted into two color difference signal data, and the above two color difference signals are synthesized using a reference clock that is four times (n = 4) the carrier frequency of the carrier color signal. However,
In the present invention, sampling is performed using a clock that is N times the frequency of the low-frequency conversion burst and converted into two color difference signal data, and the two color difference signals are synthesized using a reference clock that is twice the carrier frequency of the carrier color signal to obtain a predetermined signal. It is also possible to obtain a carrier color signal of N=
8, the data corresponding to c in Figure 5 is
Instead of repeating the four data a, b, -a, -b, a, a/√2 + b/√2, b, -a/√2
+b/√2, -a, -a/√2-b/√2, -b,
8 data of a/√2-b/√2 (general formula [a
sin (O゜+N-N'/N×360゜)+b sin(90゜+N-N'/N×360゜)], where N'=an integer from O to N)
will be repeated. The combination data of a and b as described above is one data c and the data c _-1 one clock before that, each with a constant repetition constant i,
By multiplying and adding j, k, and l, data a and b can be separated, and can be obtained, for example, as follows.

【table】

[Table] When the sampling clock is sampled at N times the frequency of the low frequency conversion burst by the above conversion, generally the sampling data c and 1
Since it is calculated from sampling data c _-1 before the clock, data mixing occurs from data b to data a or from data a to data b (hereinafter referred to as crosstalk). To prevent this, it is necessary to set the multiple N sufficiently large. It is. However, in the case of N=4, as is clear from the above explanation, 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 with a clock that is more than twice the signal frequency, and the maximum frequency after passing through low-pass filter 2 in Figure 3 is low-pass conversion. The sampling clock must be twice the frequency of the burst, and the sampling clock must be at least four times the frequency _c of the low-pass conversion burst. In addition, when converting two color difference signal data into a predetermined carrier color signal, the operation is almost the reverse of that of sampling the low frequency conversion color signal at N times the clock frequency of the low frequency conversion burst and converting it into a color difference signal. For example, when using a reference clock that is three times the carrier frequency (n = 3), esin0° + sin90° = esin120° + sin210° = √3/2e-1/2 esin240° + sin330° = -√3/2e-1/2 (General formula esin(O°+n-n'/n)+sin(90°+n-n'/n), n'=an integer from 0 to n) Three pieces of data are calculated and repeatedly output. 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 esin0゜+sin90゜= esin90゜+sin180゜=e esin180゜+sin270゜=- esin270゜+sin360゜=-e is 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 the respective data. Effects of the Invention As is clear from the above explanation, according to the present invention, 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 is not used. This method has the effect of removing the bandpass filter that would be required when performing digital processing, and also requires 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 easily digitized without any hassle. Furthermore, when sampling a low-frequency conversion color signal with a clock that is four times the frequency of the low-frequency conversion burst, processing and data are required to invert the sign of the sampling, even though the clock frequency is the minimum allowed by the sampling theorem. The two color difference signals can be separated using extremely simple hardware, in which the two color difference signals are further sampled using clocks with a frequency of 1/2 the sampling clock, each with a phase difference of 180 degrees.
The effect of reducing crosstalk between color difference signals is obtained, and even when converting two color difference signal data into predetermined carrier color signal data, by setting the reference clock to four times the carrier frequency of the carrier color signal, two This can be done simply by inverting the sign of the color difference signal and switching and outputting each data.
There are effects that can be achieved with simple hardware. Furthermore, since the comb filter passes two low-frequency color difference signals separately, it can be easily replaced with an extremely low-speed semiconductor memory, and the circuit can be miniaturized.

[Brief explanation of the drawing]

1 and 2 are block diagrams for explaining a conventional color signal reproducing method, and FIG. 3 is a block diagram of an embodiment of a color signal reproducing processing circuit using the color signal reproducing method of the present invention. FIG. 4 is a vector diagram of a low frequency conversion color signal, and FIG. 5 is a timing chart showing waveforms and data output states of various parts in FIG. 3. 1...Head, 2...Low pass filter, 3...
...ACC circuit, 18...A/D converter, 19...
Decoder, 20a, 20b...comb filter,
21... Encoder, 22... D/A converter, 2
3... Band pass filter, 24... Timing circuit, 25... Mono multivibrator, 26...
...D/A converter, 27...Voltage controlled oscillator, 28
...Crystal oscillator.

Claims (1)

[Scope of Claims] 1 N times (however, N
is a positive integer), the sampled data is converted into two color difference signal data, and the reference clock of n times the carrier frequency of the carrier color signal (where n is a positive integer) is used to convert the sampled data into two color difference signal data.
The four color difference signal data are sampled again, and each of the n circulating digital data strings corresponding to the digital values obtained when each of the quadrature carriers of the carrier color signal is sampled with the reference clock multiplied by the n times is converted into each of the color difference signal data. A color signal reproducing method characterized in that a predetermined carrier color signal is obtained by an output means that multiplies the signal and then adds the signal and outputs the resultant signal. 2. Using an A/D converter as a sampling method for low-frequency conversion color signals, 2
The above two color difference signal data are converted into two color difference signal data with carrier frequency n as digital data.
The above two color difference signal data are re-sampled with the reference clock doubled, and each of the n circulating digital data corresponds to the digital value when each of the quadrature phase carriers of the carrier color signal is sampled with the reference clock multiplied by the n times. A predetermined carrier color signal is obtained by multiplying and adding each of the color difference signals to obtain carrier color signal data, and performing D/A conversion on the carrier color signal data. 2. The color signal reproducing method according to item 1. 3. A quadruple clock locked to the burst of the low-range converted color signal is used as a sampling block for the low-range converted color signal, and the positive/negative sign of the sampling data is inverted at twice the period of the sampling clock, and the above-mentioned inversion is performed. Claim 1, characterized in that the data is further converted into two color difference signals by sampling means with two clocks each having a cycle twice that of the sampling clock and having a phase base of 180°. color signal reproduction method. 4 Using a clock four times as large as the carrier color signal as a reference clock, the output means samples the two color difference signal data f and e again using the reference clock, and then inverts the sampling data f and e and their positive and negative signs. A total of four pieces of data -f, -e are processed at each sampling period as e, f, -e,
2. The color signal reproducing method according to claim 1, wherein the color signal is sequentially switched and output in the order of -f. 5. The color difference signal reproducing method according to claim 1, wherein the low frequency conversion color signal is converted into two digital color difference signal data and then passed through a digital comb filter.