JPS61137488A - Chrominance signal processing device - Google Patents

Abstract

PURPOSE:To make the device hard to be influenced by noises in stationary time and to quicken response to a jitter by providing a demodulator for obtaining a color difference signal, a variable frequency oscillator that sets a signal in the bust period of the color difference signal to a control signal and sets an output to a carrier of the demodulator, a modulator that modulate the color difference signal again and a variable phase shifting circuit. CONSTITUTION:Out of R-Y signals obtained by a demodulator 1, signals in the burst period are extracted by a burst gate 5, and passed through an LPF6 and controls a variable frequency oscillator 7. An output of the oscillator 7 is given to the demodulator 1. Consequently, a demodulation axis is controlled by the R-Y axis and B-Y axis. Accordingly, a demodulation axis can be obtained accurately by making feedback to the demodulator 1 by the R-Y component. However, a phase error remains at the time of transient response. Above-mentioned R-Y signal and B-Y signal are quadrature two-phase modulated by a modulator 2 and outputted. At this time, an output of a fixed oscillator 4 phase of which is changed by a variable phase-shifting circuit 3 is given to the modulator. The circuit 3 changes the modulation axis of the modulator according to phase errors of the modulation axis obtained from the gate 5, and corrects phase errors generated at the time of demodulation instantaneously. This operation is made at high speed as it is made in an open loop.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color signal processing device used in a video tape recorder, which 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. 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. 4 is a block diagram showing the configuration of a conventional color signal processing device.

The reproduced low-pass converted carrier color signal is frequency-converted into a subcarrier color signal through a balanced modulator 50, and unnecessary components generated during balanced modulation are removed by a bandpass filter 51 and output as a carrier color signal. On the other hand, from the output to the burst gate 6
2, the burst is extracted and its phase is compared with the output of the reference oscillator 64 by the phase comparator 63. The phase error passes through a low-pass filter 56 to control a voltage controlled oscillator (hereinafter referred to as VC○) S6. The output of the VCO'sa is multiplied by a frequency obtained by multiplying the horizontal synchronizing signal CfH) by 40 in a PLL circuit 69 and a frequency in a balanced modulator 68, and is given as a carrier to a balanced modulator 6o through a Kundo pass filter 6γ. (For example, National Technical
report Vo119 No3 pp205~2
(June 1973) Problems to be Solved by the Invention However, in the above configuration, the balanced modulator 50° bandpass filter 51. Burst gate 52° phase comparator 6
3. Low-pass filter css, VCO 66, balanced modulator 58. The bandpass filter 67 is a negative feedback loop, that is, PL
Since it forms an L configuration, the drawbacks of PLL circuits are:
The faster the response of the loop, the more susceptible it is to noise during steady state. Therefore, in order to remove jitter from the reproduced low-frequency conversion carrier color signal, if the followability to the shifter, that is, the response of the loop, is increased too much, the response performance will be limited because the performance will deteriorate due to the influence of noise. It had

In view of the above-mentioned problems, the present invention provides a color signal processing device that can speed up the response to jitter, that is, the transient response, without being susceptible 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 includes a demodulator that demodulates a low-pass conversion carrier color signal into a color difference signal;
A variable frequency oscillator that uses the burst period signal of the color difference signal as a control signal and uses the output as a carrier for a demodulator, a modulator that modulates the color difference signal again, and a control signal that uses the burst period signal of the color difference signal as the control signal. A variable phase shift circuit for changing the phase of a signal is provided, and a signal obtained by changing the phase of the output of a fixed oscillator by the variable phase shift circuit is used as the carrier of the modulator.

According to the above-described configuration, when the low frequency conversion carrier color signal is demodulated into a color difference signal by the demodulator, the carrier supplied to the demodulator is supplied from a variable frequency oscillator, and the carrier is variable depending on the burst period signal of the color difference signal. A negative feedback loop is formed by controlling the frequency oscillator to perform synchronous demodulation. At that time, the residual phase error of the demodulation axis that could not be removed by the negative feedback loop is removed by changing the phase of the carrier given to the modulator during modulation according to the burst period signal of the color difference signal using a variable phase shifter. , to obtain a jitter-free carrier color signal.

EXAMPLE An example 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. The reproduced low-pass conversion carrier color signal is demodulated by a demodulator 1 into two color difference signals, an RY signal and a BY color code.

At this time, the burst period signal of the R-Y signal is extracted by the burst gate 6, passes through the low-pass filter 6, and controls the variable frequency oscillator 7. The output of the variable frequency oscillator 7 is given as a carrier to the demodulator 1. As a result, the demodulation axes of the demodulator are controlled to be the RY axis and the BY axis, and the principle thereof will be explained with reference to FIG. 2. Figure 2 shows R-
It is a vector diagram showing the Y-axis, the BY-axis, and the phase of the burst signal, where a is a vector diagram when the demodulation is correctly performed, and b is a vector diagram when the demodulation axis is shifted by θ. As can be seen from FIG. 2A, the burst signal is orthogonal to the RY axis, and if demodulated using an accurate demodulation axis, the RY axis component will be zero. On the other hand, when the demodulation axis is shifted, an RY component appears as shown in b. Therefore, since the R-Y component of the burst represents the phase error of the demodulation axis, the R-Y component of the burst signal is
By applying negative feedback to the demodulator 1 using the Y component, the demodulation axis can be accurately obtained. However, since the above operation is performed in a negative feedback loop, a phase error remains during the transient response. Next, returning to FIG. 1, the operation of removing these phase errors during modulation will be explained. R- demodulated as described above
The Y signal and the B-Y signal are subjected to quadrature two-phase modulation by a modulator 2 and output as a carrier color signal. At this time, the carrier is the output of the fixed oscillator 4 whose phase is changed by the variable phase shift circuit 3 and is applied to the modulator. The variable phase shift circuit 3 changes the modulation axis of the modulator according to the phase error of the demodulation axis obtained from the burst gate 6, and instantaneously corrects the phase error generated during demodulation. Since this operation is performed in an open loop, it is much faster than the conventional method using only a negative feedback loop. As described above, a jitter-free carrier color signal is obtained at the output of the modulator 2.

Next, a specific example of the variable phase shift circuit described above will be explained with reference to FIG. 1o is a changeover switch,
11 to 1 are logic buffers. The input signals are input to logic buffers 11 to 17 connected in series. The input signals gate-delayed by each logic buffer are selected by a changeover switch 10 and outputted according to the control input. In this embodiment, the number of logic buffers is seven, but the number may be set depending on the amount of phase change. Since this embodiment can be constructed with only logic circuits, I
Can be easily converted to C. In addition, in FIG. 1, if the low-frequency conversion carrier color signal is a ~Φ-converted digital signal and the demodulation is performed digitally, the control signal for the variable phase shift circuit 3 will be a digital signal. Connection with a phase shift circuit becomes easy.

Effects of the Invention As described above, the present invention includes a demodulator that demodulates a carrier color signal that has undergone low frequency conversion into a color difference signal, a variable frequency oscillator that is controlled by obtaining a phase error of the demodulation axis from the color difference signal, and a demodulator that demodulates a color difference signal. By providing a variable phase shift circuit that changes the phase of the carrier of the modulator using a signal representing the phase error between the modulator that modulates and the demodulation axis obtained from the color difference signal, transients that cannot be eliminated using a negative feedback loop can be eliminated. By instantaneously correcting state and steady-state phase errors in an open loop, a jitter-free carrier color signal can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color signal processing device according to an embodiment of the present invention, FIG. 2 is a vector diagram showing the relationship between the demodulation axis and burst, and FIG. 3 is a configuration diagram showing a specific example of a variable phase shift circuit.
FIG. 4 is a block diagram of a conventional color signal processing device. 1...Demodulator, 2...Modulator, 3...
...Variable phase shift circuit, 1o...Selector switch, 11-17...Logic buffer, 5o
... Balanced modulator, 53 ... Phase comparator.

Claims (3)

[Claims] (1) a demodulator that demodulates a low-pass converted carrier color signal including a burst signal into a color difference signal; and a variable frequency oscillator that uses a burst period signal of the color difference signal as a control signal and outputs it as a carrier of the demodulator. , comprising a modulator that modulates the color difference signal, and a variable phase shift circuit that changes the phase of the input signal using a burst period signal of the color difference signal as a control signal, and the output of the fixed oscillator is transmitted to the variable phase shift circuit. A color signal processing device characterized in that the color signal processing device is configured to provide the signal as a carrier to the modulator through the color signal processing device. (2) The color difference signal is the R-Y signal and the B-Y signal, and the signal for controlling the variable frequency oscillator and the variable phase shift circuit is a burst period signal of the R-Y signal. The color signal processing device according to scope 1. (3) The variable phase shift circuit includes a plurality of logic buffer circuits connected in series and a switch circuit that selects one of the outputs of each of the logic buffer circuits, and the input and output of the variable phase shift circuit. are the input of the first stage and the output of the final stage of the plurality of logic buffer circuits connected in series, respectively, and the switch circuit is configured to be switched by a control signal. Color signal processing device.