JPH0435390A - Color signal processor unit - Google Patents

Abstract

PURPOSE:To improve color picture quality due to high frequency jitter without losing crosstalk suppression performance by compensating jitter only by a PLL receiving a horizontal synchronizing signal and improving crosstalk disturbance with an azimuth loss. CONSTITUTION:A phase comparator 15, a low pass filter 16, a voltage controlled oscillator 17, and a 1/N frequency divider 19 form a known PLL, a horizontal synchronizing signal H is applied to one input of the phase comparator 14, the output signal frequency of the control circuit 17 is frequency-divided into 1/N by the 1/N frequency divider 19 and the result is added to the other input of the phase comparator 15, then a signal synchronously with the horizontal synchronizing signal and having a frequency of a multiple of N of that of the horizontal synchronizing signal is outputted from the voltage controlled oscillator 17. Thus, jitter is compensated by using only the PLL receiving the horizontal synchronizing signal and crosstalk disturbance is improved by an azimuth loss, then jitter improving degree is expanded up to a high frequency without caring about crosstalk disturbance.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a video signal recording and reproducing system that employs a low-frequency conversion color signal recording and reproducing method, and in particular, the present invention relates to a video signal recording and reproducing system that employs a low-frequency conversion color signal recording and reproducing method. The present invention relates to a color signal processing device that converts to a low frequency band and converts from a low frequency band to a high frequency band during reproduction.

[Conventional technology]

As a conventional color signal processing device of this type, there is one shown in FIG. This is intended for application to a consumer videotape footer that records azimuthally on a 172-inch videotape using helical scanning. In the figure, a frequency converter 1 receives a color signal as one input, receives a local signal as the other input, and outputs a frequency deviation component obtained by subtracting the color signal frequency from the local signal frequency, which is then added to a comb filter 2. The comb filter 2 removes crosstalk from adjacent tracks during playback and applies it to the color cow circuit 3. color killer circuit 3
removes the output from this circuit when broadcasting in black and white or when receiving weak radio waves to prevent color noise from appearing on the screen. In addition, in order to generate a local signal for the frequency converter 1, a PLL and a color process circuit 4 are provided which receive a horizontal synchronization signal H and a drum pulse DP, which is a switching signal for the rotary head, and generate a low frequency converted color signal. 0, whose output is applied to the frequency converter 5.
The PLL section that constitutes the LL and color process circuit 4 is as follows:
This is the part that generates a low-frequency conversion color signal synchronized with the horizontal synchronization signal H, and the color processing part performs phase soft processing to reduce crosstalk interference from adjacent tracks during playback due to azimuth recording. In this section, the phase shift state of the low-frequency conversion color signal is changed for each field by the drum pulse DP. On the other hand, the burst gate 7 takes in a color signal input during recording via the changeover switch 6, takes in the color signal input during playback (takes in the output of the rectangular filter 2, extracts each color burst, and outputs a color burst from the phase comparator 10 and 14. Among these, the phase comparator lO is connected to the APC (AUTOMATICPH) together with the low-pass filter 11 and the voltage-controlled crystal oscillator 12.
The output of the voltage controlled crystal oscillator 12 is applied to the frequency converter 5.

In this case, the output of the voltage-controlled crystal oscillator 12 is fed back during recording and added as the other input of the phase comparator 10 via a changeover switch 9 that switches between recording and playback, and is used instead of the feedback signal during playback. is applied as the output of the crystal oscillator 8 or the other input of the phase comparator 10. Therefore, the voltage-controlled crystal oscillator 12 outputs a signal that is locked to the color burst of the input color signal during recording and to the fixed oscillation frequency of 3.58 MHz of the crystal oscillator 8 during reproduction. The frequency converter 5 outputs the frequency component of the sum of the 3.58 MHz color subcarrier frequency from the voltage controlled crystal oscillator 12 and the low-frequency conversion color frequency of the PLL and color process circuit 4 described above, and as a local signal. As a result, the frequency converter 1 converts the input color signal (3.58M) Iz and the signal from the voltage-controlled crystal oscillator 12 (3.58MHz) into canceled PL.
Outputs the low color frequency signals of L and color processing circuit 4, and outputs the low color frequency signals and PL reproduced during playback.
The output frequency of the voltage controlled crystal oscillator 12 at which the frequency of the signal of L and the color process circuit 4 are canceled, that is,
3.58M) lz color signal is output. Note that the phase comparator 14 detects the phase continuity of the color burst based on the color burst of the burst gate 7 and the continuous signal inputted via the phase shifter 13, and if there is continuity, the color signal is detected. If there is no continuity, a discrimination signal is generated that determines that there is no color signal. The color killer circuit 3 removes the color signal according to this discrimination signal.

[Problem to be solved by the invention]

The conventional color signal processing apparatus described above has a problem in that the more crosstalk interference between adjacent tracks of the reproduced low-frequency color signal is attempted to be reduced, the worse the degree of improvement in color image quality by removing jitter components becomes. This will be explained in detail below.

Since the PLL and color process circuit 4 are sampling systems of 15.73KHz, the sampling frequency alone is 7.9K, which is 172 of the sampling frequency.
The phase delay of the loop-circular transfer function at Hz is about 70 degrees. Moreover, delays of other circuit elements are added to this phase delay. Therefore, if a phase margin and a gain margin are provided to ensure operational stability of the loop in consideration of these phase delays, the frequency response of the roof becomes approximately 3 KHz or less, and in many cases approximately IKHz. Therefore, high-frequency jitter components of IKHz or higher due to tape vibration are not sufficiently canceled out by the frequency converter 1 and remain.

Further, since the sampling frequency of the APC consisting of the phase comparator lO1 low-pass filter 11 and the voltage-controlled crystal oscillator 12 is the same as that of the PLL and color process circuit 4 described above, it is not useful for improving jitter.

On the other hand, the reproduced low-frequency color signal is subject to crosstalk interference from adjacent tracks. To deal with this crosstalk interference, PS (
By adopting PHASE 5HIFT), the frequency spectrum pattern of crosstalk from adjacent tracks is inserted into the subsequent stage of frequency converter 1 in the form of line interleaving so that it has a line anti-correlation relationship with the original color signal. It is removed by filter 2. However, some influence still remains due to the accuracy of the rectangular filter and the limit on the accuracy of keeping the tape speeds for recording and playback the same or -.Originally, the image quality of color signals, especially the quality of hue, Although it is extremely sensitive to the stability of the phase of the reference color burst, if crosstalk cannot be completely removed, the image quality will deteriorate accordingly.

Therefore, in order to further reduce the influence of crosstalk,
When a comb filter is inserted into the APC loop, the operation of the loop becomes unstable unless the cutoff frequency of the loop response is lowered due to the influence of the l-line delay component caused by the comb filter, resulting in significant hue deterioration. However, if the cutoff frequency is lowered, the operation of the loop becomes stable, but the degree of improvement in high-frequency jitter deteriorates.

However, if the <C-shaped filter is placed outside the APC roof, the loop response will be improved, but the degree of deterioration of color image quality due to the influence of crosstalk will increase.

On the other hand, since the above-mentioned phase comparator IO handles a 3.58 MHz signal, a double balanced modulator as shown in FIG. 5 is used. Since this is a kind of exclusive OR circuit, when the phase difference between signal A and signal B in Figure 6 (a> A signal C corresponding to The signal B' becomes a ripple.On the other hand, if the integral constant is made thicker (then A
The cutoff frequency of the PC loop is lowered, the response becomes worse, and the degree of improvement in high-frequency jitter becomes worse as stable operation of the loop is ensured.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a color signal processing device that can improve color image quality due to high-frequency jitter without impairing crosstalk suppression performance.

[Means to solve the problem]

A color signal processing device according to the present invention includes a first frequency converter that inputs a color signal and a local signal and outputs a frequency deviation component of these two signals; A PLL that generates a signal with a frequency that is an integer multiple of the signal, a phase modulator that uses the signal generated by this PLL as the input signal and the phase error signal of this PLL as the modulation input, and oscillates at a fixed frequency. an oscillator, the output of this oscillator, and the output of the phase modulator are input, and the sum component of these two signals is outputted to generate the first signal.
and a second frequency converter that converts the local signal into a local signal of the frequency converter.

[For production]

In the present invention, jitter is compensated for by using only the PL level of the horizontal synchronization signal, and crosstalk interference is improved by azimuth loss. It is possible to prevent interference due to crosstalk when the comb filter is placed outside the APC loop, and thereby the degree of jitter improvement can be extended to high frequencies without worrying about crosstalk interference.

〔Example〕

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, the same reference numerals as in FIG. 4 indicate the same elements. This device eliminates APC using color burst, which constitutes the conventional device, and instead compensates for jitter using only PLL using a horizontal synchronization signal. Here, the phase comparator 15,
A well-known PLL is configured by a low-pass filter 16, a voltage controlled oscillator 17 and an l/N frequency divider 19, and a phase comparator 1
5, and the output signal frequency of the voltage controlled oscillator 17 is applied to the l/N frequency divider 19.
By dividing the frequency into l/H by and adding it as the other input of the phase comparator 15, it is synchronized with the horizontal synchronizing signal, and
A signal having a frequency N times that of the horizontal synchronizing signal is output from the voltage controlled oscillator 17. The output from this voltage controlled oscillator 17, ie, the output signal of the PLL, is applied to a color processing circuit 18. The color process circuit 1g performs phase shift processing on the drum pulse DP to reduce crosstalk interference from adjacent tracks during playback, and applies it to the phase modulator 21 as a carrier input.

Further, the phase error signal output from the phase comparator 15 is adjusted by a gain adjustment circuit 20 and added as a modulation input to a phase modulator 21. The phase modulation signal thus generated is combined with the output of the crystal oscillator 8 in the frequency converter 5, and the frequency addition component of both signals is added as a local signal of the frequency converter 1.

Further, the output of the phase comparator 10 is output from the voltage controlled crystal oscillator 12.
The output of this voltage controlled crystal oscillator 12 is applied to a phase comparator 10 and a phase shifter 13.

FIG. 2 shows a specific example of the configuration of the phase modulator 21.

In the figure, one end of a resistor R is connected to the emitter A of a transistor Q whose base serves as an input end for a carrier signal, and the other end of this resistor R is connected to an output end C.

Furthermore, a variable capacitance diode D1, a capacitor C1, and an inductor LO are connected in series between the flipter B and the output terminal C of the transistor Q. Furthermore, the variable capacitance diode D
and the mutual junction of capacitor C1.

The input end of the modulation signal is connected to the movable terminal of the variable resistor VR via the capacitor C2.

In FIG. 2, variable capacitance diode D, capacitor CI and inductor LO form a series resonant circuit. Among these, the junction capacitance of the variable capacitance diode D changes depending on the modulation input signal. Further, the reactance of the series resonance at the carrier frequency changes from the capacitive range to the inductive range due to a change in the junction capacitance of the variable capacitance diode D. Therefore, as shown in FIG. 3, the vector locus of the output signal of output terminal C is
Draw a circle with diameter.

The maximum phase shift is determined by the maximum amount of jitter in the reproduced signal, so if this is large, the required number of phase modulators shown in FIG. 2 may be connected in cascade.

As explained above, according to this embodiment, the burst-based APC used in the conventional device is eliminated, which reduces image quality deterioration and loop response that would otherwise occur when a comb filter is provided to remove crosstalk. Deterioration can be avoided.

Further, according to this embodiment, the PLL by the horizontal synchronization signal
However, since the crosstalk interference of the horizontal synchronizing signal is improved by the azimuth loss, the above-mentioned problems of deterioration of image quality and deterioration of loop response do not occur.

On the other hand, regarding the improvement of the problem of PLL response limit due to sampling and holding, PLL voltage controlled oscillator 17
A high-speed response is achieved using an oven loop by phase modulating the output of the PLL with a phase modulator 21 that uses the phase error of the PLL as a modulation input.

Furthermore, since the PLL phase comparator handles a low frequency of 15.73 KHz, a sampling and holding circuit can generally be used, so that a phase error signal with less ripple can be obtained as the output.

〔Effect of the invention〕

As is clear from the above description, according to the present invention,
Since jitter is compensated for only by PLL using a horizontal synchronization signal, and crosstalk interference is improved by azimuth loss, the degree of jitter improvement can be extended to high frequencies without worrying about crosstalk interference.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. 2 is a circuit diagram showing the detailed configuration of the main elements of the same embodiment, FIG. 3 is a vector diagram for explaining the operation of the same elements, and FIG. 4 is a diagram of a conventional color signal processing device. FIG. 5 is a block diagram showing the configuration, FIG. 5 is a circuit diagram showing the detailed configuration of the main elements of the device, and FIGS. 6A and 6B are waveform diagrams for explaining the operation of the device. 1.5... Frequency converter, 2... Comb filter, 3... Color killer circuit, 6... Changeover switch, 7... Burst gate, 8... Crystal oscillator, 1o
...Phase comparator, 14.15...Phase comparator, 1
2.17... Voltage controlled oscillator, 13... Phase shifter, 1
6...Low pass filter, 18...Color process circuit, 19...17N frequency divider, 20...Gain adjustment circuit,
21...Phase modulator. Inventor: Yoshiteru Kosaka Applicant: Victor Japan Co., Ltd.

Claims (1)

[Claims] (1) A color signal and a local signal are input to a color signal processing device that converts the frequency of the color signal from high frequency to low frequency during recording and from low frequency to high frequency during playback,
a first frequency converter that outputs a frequency deviation component of these two signals; a PLL that generates a signal that is synchronized with a horizontal synchronization signal and has a frequency that is an integral multiple of the horizontal synchronization signal; a phase modulator that uses the signal obtained as a carrier input and a phase error signal of the PLL as a modulation input, an oscillator that oscillates at a fixed frequency, and an output signal of the oscillator and an output signal of the phase modulator. , and a second frequency converter that outputs an added component of these two signals and uses it as a local signal of the first frequency converter.