JPH044799B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a color signal processing device used in a video tape recorder that converts a color signal into a low frequency signal and records and reproduces the signal.

2. Description of the Related Art In recent years, demand for video tape recorders has increased, and improvements in color signal processing performance have been desired. In consumer video tape recorders, the sub-carrier color signal is frequency-converted to a low-pass converted carrier color signal and recorded, and during playback, the frequency is converted again and returned to the carrier color signal, and at that time, the color generated by the jitter of the rotating cylinder is recorded. A method called color under was used to remove jitter from the signal.

A conventional color signal processing device will be described below with reference to the drawings. FIG. 3 is a block diagram showing the configuration of a conventional color signal processing device.

The reproduced low-pass conversion carrier color signal is sent to a balanced modulator 5.
0, the signal is frequency-converted into a subcarrier color signal, crosstalk from adjacent tracks is removed by a comb filter 60, unnecessary components generated during balanced modulation are removed by a bandpass filter 51, and the signal is output as a carrier color signal. do. On the other hand, from the output to the burst gate 5
2, the burst is extracted and its phase is compared with the output of the reference oscillator 54 by the phase comparator 53. The phase error passes through a low pass filter 55 to control a voltage controlled oscillator (hereinafter referred to as VCO) 56. VCO5
The output of 6 is the horizontal synchronizing signal (f _H ) by the PLL circuit 59.
The frequency multiplied by 40 is added to the frequency by the balanced modulator 58, and the result is given as a carrier to the balanced modulator 50 through the bandpass filter 57. (For example, National Technical Report Vol. 19 No. 3
PP205-216 June 1973) Problems to be Solved by the Invention However, in the above configuration, the balanced modulator 5
0, comb filter 60, band pass filter 5
1, burst gate 52, phase comparator 53, low pass filter 55, VCO 56, balanced modulator 58,
The bandpass filter 57 forms a negative feedback loop, i.e.
Since it has a PLL configuration, it has the characteristic of becoming unstable when the loop response is made faster, which is a drawback of PLL circuits. Moreover, since a comb filter is included in the loop, speeding up the response tends to make it even more unstable. Therefore, in order to remove jitter from the reproduced low-frequency conversion carrier color signal, if the jitter followability, that is, the loop response, is made too fast, the problem becomes unstable and the performance deteriorates due to the influence of noise. However, the response performance was limited.

In view of the above-mentioned problems, the present invention provides a color signal processing device capable of speeding up the response to jitter, that is, the transient response, without increasing the susceptibility to noise during steady state.

Means for Solving the Problems In order to solve the above problems, the color signal processing device of the present invention performs A/D (analog-to-digital) conversion of a low-frequency conversion carrier color signal, and then converts the RY signal and the B- Y
A demodulator that demodulates the signal, a comb filter that passes the output of the demodulator, and a first burst that extracts the burst period signals of the R-Y signal and B-Y signal obtained at the output of the comb filter, respectively. a gate circuit, a second burst gate circuit, a variable frequency oscillator that is controlled by a signal obtained by D/A converting the output of the first burst gate circuit and supplies clocks for the A/D converter and demodulator; Let the outputs of the first burst gate and the second burst gate be b and a, respectively, and R-Y of the output of the comb filter.
When the signal and B-Y signal are Y and X, respectively,
an arithmetic circuit that inputs and Y and outputs -Xa-Yb and Xa-Yb; a modulator that modulates the output of the arithmetic circuit in quadrature two-phase; and a D/A that converts the output of the modulator into D/A.
It is composed of A converters.

Effects With the above configuration, the present invention performs A/D conversion on the low frequency conversion carrier color signal, and converts the RY signal and B-Y signal in the demodulator.
The signals are demodulated and passed through a comb filter. At this time, the clocks of the A/D converter and demodulator are
The signal is supplied from a variable frequency oscillator controlled by the burst period signal of the RY signal after passing through a comb filter to form a negative feedback loop and control the demodulation axis. Furthermore, the phase error of the demodulation axis of the demodulator during the transient response that could not be removed by this negative feedback loop is expressed as b and a for the burst period signals of the R-Y signal and B-Y signal, respectively, and R
- When the Y signal is Y and the B-Y signal is X, X is -
Xa−Yb, by converting Y to Xa−Yb, R
-Y signal and B-Y signal vectors are rotated and removed, modulated again, and then D/A converted and output to obtain a jitter-free carrier color signal.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a color signal processing device according to an embodiment of the present invention. In the figure, the thick line indicates the flow of digital signals, and the solid line indicates the flow of analog signals. The reproduced low frequency conversion carrier color signal is converted into a digital signal by an A/D converter 1, and demodulated into a R-Y signal and a B-Y signal by a demodulator 2.
The R-Y signal Y and B-Y pass through the comb filter 3.
The signal becomes X. The R-Y signal Y and the B-Y signal
is obtained. Output signal b of burst gate circuit 7
is D/A converted by a D/A converter 9, passes through a low-pass filter 10, controls a variable frequency oscillator 11, and its output is supplied to the A/D converter 1 and demodulator 2 as a clock. As a result, demodulator 2, comb filter 3, burst gate circuit 7, D/A converter 9, low pass filter 10, variable frequency oscillator 1
1, feedback is applied so that the output b of the burst gate circuit 7 becomes zero.
Since the vector of the burst signal is orthogonal to the R-Y signal, if the demodulation axis is correct, the output b of the burst gate circuit 7 will be zero, so the feedback loop described above will demodulate the R-Y signal and the B-Y signal. can do. FIG. 2 shows the relationship between the burst and the demodulation axis just described. FIG. 2a shows an example of the RY axis, the BY axis, the burst signal, and the color signal when demodulated using accurate demodulation axes. As can be seen from the figure, the burst signal is orthogonal to the RY axis, so the RY axis component is zero. Further, the color signal vector has x and y components, which change from moment to moment, but here an example of a vector at a certain time is shown.

By the way, as mentioned earlier, the demodulation axis is controlled by a negative feedback loop, so a finite settling time is required for transient response, and until the transient response settles, the burst and color signal vectors are It will have a phase error with respect to the normal vector. This situation is shown in FIG. 2b. In this figure, the burst signal vector is rotated by an angle from the normal vector. Therefore, the color signal vectors x' and y' are also shown in Fig. 2a.
It is rotated by an angle from the color signal vectors x and y shown in . Therefore, the color signal vectors x' and y' in FIG. 2b can be instantly returned to their normal positions by reversely rotating the angle. The arithmetic circuit 4 shown in FIG. 1 performs this. Next, the calculation method in this calculation circuit will be explained. As just explained, with respect to the regular color signals x, y, if the color signals with phase errors are x', y', and the phase error is, then the vectors x, y are Since it is rotated, the following relationship holds from the formula for vector rotation.

x=x′cos−y′sin…(1) y=x′sin+y′cos…(2) Also, if the absolute value of the burst signal vector in Fig. 2b is 1, the R-Y axis component β is sin. Yes, B-
The Y-axis component α is −cos. This relationship is expressed as equation (1),
If used in equation (2), the following equations (3) and (4) are obtained.

x=-x'α-y'β...(3) y=x'β-y'α...(4) Therefore, returning to FIG. 1, the inputs X and Y of the arithmetic circuit 4 are (3 ), x′ in equation (4),
y', and the outputs b and a of the burst gate circuits 7 and 8 correspond to β and α in equations (3) and (4), respectively, so the arithmetic circuit 4 calculates equations (3) and (4). Therefore, by performing calculations and outputting -Xa-Yb and Xb-Ya, the phase error can be removed using the above-mentioned principle. The signal from which the phase error has been removed in this manner is sent to the modulator 5, subjected to D/A conversion by the D/A converter 6, and output as a carrier color signal free of phase error, that is, free of jitter. In the above description, the absolute value of the burst signal is assumed to be 1, but if the absolute value is A, the two output levels of the arithmetic circuit 4 are simply multiplied by A, and there is no problem in operation.

Effects of the Invention As described above, the present invention converts a carrier color signal that has undergone low frequency conversion into a digital signal using an A/D converter, and then demodulates it by controlling the demodulation axis using a negative feedback loop. A jitter-free carrier color signal can be obtained by removing the phase error during transient response by instantly rotating the color signal vector through calculation, re-modulating it, performing D/A conversion, and outputting it. can. Furthermore, since the calculation for rotating the vector of the color signal is performed digitally, accurate calculation can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a color signal processing device in an embodiment of the present invention, FIG. 2 is a vector diagram showing the relationship between the demodulation axis, burst signals, and color signals, and FIG. 3 is a conventional color signal processing method. FIG. 2 is a block diagram showing the configuration of the device. 1...A/D converter, 2...Demodulator, 4...Arithmetic circuit, 5...Modulator, 6...D/A converter, 5
0...Balanced modulator, 53...Phase comparator.

Claims (1)

[Claims] 1 An A/D converter that performs A/D (analog-digital) conversion of a carrier color signal that has been low-pass converted and includes a burst signal;
a demodulator that demodulates the Y signal and the B-Y signal, and the R
- a comb filter that passes the Y signal and the B-Y signal, respectively, and a first burst gate that takes out the burst period signals of the R-Y signal and the B-Y signal obtained at the output of the comb filter; circuit, a second burst gate circuit, a first D/A conversion circuit for D/A converting the output of the first burst gate circuit, and the first D/A conversion circuit controlled by the first D/A conversion circuit; A variable frequency oscillator that supplies clocks for the A/D converter and the demodulator, and outputs of the first burst gate and the second burst gate as b and a, respectively, and a R-Y signal of the output of the comb filter. When Y is Y and the B-Y signal is X, there is an arithmetic circuit that inputs X and Y and outputs -Xa-Yb and Xa-Yb, a modulator that modulates the output of the arithmetic circuit in quadrature two-phase, and the modulator. 1. A color signal processing device comprising a second D/A conversion circuit that converts the output of the device into a D/A converter.