JPS59160392A - Color jitter correcting circuit of video disk reproducing device - Google Patents

Abstract

PURPOSE:To obtain a follow-up characteristic sufficient for a color jitter component by removing the jitter component from a video signal through an APC loop and then separating only a color signal component by a comb-shaped filter. CONSTITUTION:The APC loop relating to the removal of the jitter component is composed of the 1st frequency converting circuit 3, a band-pass filter 4, an ACC circuit 6, a phase detecting circuit 7, and a VCXO circuit 8, and the output of the band-pass filter 4 is impressed to the 1st comb-shape filter 5. Consequently, when the color signal component in the output signal of an FM detector 2 varies with the jitter component to vary the color signal component in the output signal of a frequency converting circuit 3, the variation is absorbed completely by the APC loop. Then, an adding circuit 11 adds the color signal output of the filter 5 to a luminance signal from the 2nd comb-shaped filter 10 to output a video signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color jitter correction circuit for a video disc playback device. One type of video disc is a so-called capacitance change type video disc in which information is recorded as changes in capacitance. . In such a video disc playback device that detects recorded information from a video disc, a pickup needle detects a change in capacitance between the surface of the video disc and a pickup needle placed opposite to the surface of the video disc. Then, the detected signal is then subjected to appropriate signal processing to obtain a video signal and an audio signal.

By the way, the video disc on which the above signal is recorded has
Slight eccentricity and distortion of the video disc itself9
There is surface wobbling, and the motor provided in the video disc playback device for rotating the video disc has uneven rotation. Therefore, the playback signal played back from the video disc will contain jitter components.

For this reason, in conventional video disc playback devices,
It had a time axis correction system for the reproduced signal and was designed to absorb its jitter components. Generally, jitter components included in color signals are reduced by automatic phase control (APC>loop, which will be described next with reference to FIG. 1).

However, the A P
As will be described later, the C loop has the disadvantage that it cannot sufficiently follow color signals with large jitter components and cannot obtain high-quality color signals.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide an improved color jitter correction circuit capable of upwardly removing jitter components from a reproduced color signal and obtaining a high quality color signal.

This invention, simply put, AP'C, l rape,
Consists of a station wave number conversion circuit, a bandpass filter, an Ace circuit, a phase detection circuit, and a voltage-controlled oscillator circuit.The APC loop is fed with a video signal picked up from a video disc, and the jitter components contained in the video signal are removed. This is a color jitter correction circuit that then uses a rectangular filter to separate only the color signal components from the video signal from which the jitter components have been removed.

The above-mentioned objects and features of the present invention will be more clearly understood from the following embodiments of the present invention compared with conventional examples, which will be explained with reference to the drawings.

FIG. 1 is a schematic block diagram of m video processing systems of a conventional embedded subcarrier type video disc playback device. Referring to FIG. 1, the configuration and operation of a video processing system of a conventional video disc playback device will be described. For convenience of explanation, the present invention will be described as an NTSC video disc playback device.

For embedded subcarrier type video discs, the color signal has a subcarrier frequency of 3.3 in the NTSC system. ,'57
9545M)-12 (hereinafter, this frequency will be referred to as to)
Instead, it is low frequency converted to a predetermined frequency f, FM modulated together with the luminance signal, and recorded on a video disc.

In FIG. 1, a disc signal pickup unit 1 detects static signal between a rotating video disc (not shown) and a pickup needle (not shown). A change in capacitance is detected, and the detected signal is converted into an electrical signal and output as an FM signal.

The FM signal output from the disk signal pickup section 1 is subjected to FM detection by an FM detector 2. As mentioned above,
The color signal recorded on the video disc is 'l cycle:
Since it is recorded after being low-pass converted to the It number, the output signal of the FM detector 2, considering only the video fg@, consists of a luminance component and a color signal at a frequency of t.

The first frequency conversion circuit 3 receives the signal from the FM detector 2 . A video signal including the luminance signal component and the color signal component having a frequency of f is processed using a voltage controlled crystal oscillator (VCXO) described later.
X' tal 0scilato, r) ) 8
The signal is heterodyned together with the @ signal sent from the signal and performs frequency conversion. In other words, if we focus only on the color signal,
The color signal is converted from the frequency r, to the frequency [0 and output.

In the first frequency conversion circuit 3, the bandpass filter 4 includes:
This is for removing spurious generated due to the frequency conversion, and is configured to pass only frequency components near the frequency to.

The first comb filter 5 is a filter configured to have a pass characteristic at a frequency that is an odd multiple of 1/2 of the horizontal scanning frequency. This filter separates only the color signal component from the signal output from the bandpass filter 4.

That is, the comb filter 5 removes the luminance signal contained in the output signal of the bandpass filter 4.

The output of the first comb filter 5 containing only the color signal component is then given to the ACC circuit 6 and the second frequency conversion circuit 9.

The ACC circuit 6 is a circuit that adjusts the amplitude of the color signal output from the comb filter 5 to a constant level. The phase detection circuit 7 is a continuous wave applied from a crystal oscillator circuit (not shown) that generates a reference signal f, and detects the reference color subcarrier distribution (burst signal) of the color signal output from the ACC circuit 6. Phase detection is performed. The output signal of this phase detection circuit 7 is applied to a VCXO circuit 8. Then, the vcxo circuit 8 oscillates a frequency according to the voltage input from the phase detection circuit 7 and provides it to the first frequency conversion circuit 3 and the second frequency conversion circuit 9. The center frequency of the oscillation frequency of this VCXO circuit 8 is set to be (fo+f+). Therefore, the color signal of the output signal of the first frequency conversion circuit 3 has a frequency of fo.

As explained above, in the conventional circuit, the first frequency conversion circuit 3. Bandpass filter 4. First comb filter5.
The ACC circuit 69, phase detection circuit 7, and vcxo circuit 8 constitute an APC loop, which absorbs jitter components of the color signal.

The second frequency conversion circuit 9 heterodynes the output signal from the first comb filter 5 and the output signal from the vcxo circuit 8, and converts the color signal of the frequency to the second comb filter 10. output to.Second comb filter 1
0, the output signal from the second frequency conversion circuit 9 is used to remove a color signal having a frequency of t from the output signal of the FM detector 2. Therefore, the second comb filter 10 outputs only the luminance signal component of the reproduced video signal.

The adder circuit 11 adds the color signal output from the ACC circuit 6 and the luminance signal from the second comb filter 10, performs predetermined signal processing, and sends a signal to a video display device (not shown). Send out.

The conventional APC loop configured as described above has the following drawbacks. That is, if the signal picked up by the disk signal pickup unit 1 contains jitter, the frequency of the color signal component included in the output signal of the FM detector 2 will not always be constant at f, -, and f , it fluctuates around . Therefore, the color signal component in the output signal of the first frequency conversion circuit 3 also fluctuates.

On the other hand, since the comb filter 5 that separates the luminance signal component and the color signal component has a fixed comb characteristic, if the input color signal fluctuates from fO, it will undergo a large phase fluctuation.

For this reason, the closed loop characteristics of the conventional APC loop have a peak around 2 to 3 KHz, as shown in FIG. 3, making the system unstable as a control system. Moreover, there is a problem in that not only the following characteristics for jitter components are poor, but also the S/N ratio of the color signal obtained by this control system is also poor.

FIG. 2 is a schematic block diagram of an embodiment of the present invention drawn in contrast with FIG. 1. The feature of FIG. 2 is that the APC loop involved in removing jitter components is connected to the first frequency conversion circuit 3. Bandpass filter 4. It is constructed of an ACC circuit 61, a phase detection circuit 7, and a VCXO circuit 8, and the output signal of the bandpass filter 4 is applied to a first comb filter 5 disposed outside the APC loop.

Furthermore, the output signal of this first comb filter 5 is applied to the second ACC circuit 60, and the output of this ACC circuit 60) is applied to the groove 1 as shown in the addition circuit 11:2 application JFLb. be.

Note that the circuit configuration of other parts is similar to the conventional configuration shown in FIG. 1, and the same parts are given the same numbers.

By configuring as shown in FIG. 2, A! ] The C loop is the first comb filter 5 [It is not affected by the power fluctuation due to the second filter and has good closed-loop characteristics. That is, the color signal component included in the civil signal of the FM detector 2 modulates the jitter component (=Yotsu'C), and the color 18 component component θ in the output signal of the frequency conversion circuit 3 fluctuates. Figure 2 shows that the variation is completely absorbed by the APC loop, and Figure 4 shows the closed loop characteristics of the PC loop.
As shown in the figure, the closed-loop characteristic of the APC loop has no peaks, is stable as a control system, and can produce a non-normal image with a high S, /i< ratio. Furthermore, even when the jitter component is large, the follow-up characteristics for the jitter component can be improved by using the PC loop 41.

It should be noted that although the above-mentioned embodiment has been explained by taking an NTSC system video disk reproducing apparatus as an example, it goes without saying that the subcarrier frequency etc. will change in the case of other systems.

As described above, the present invention incorporates the APC loop involved in reducing color jitter into a frequency conversion circuit.

It consists of a bandpass filter, an ACC circuit, a phase detection circuit, and a voltage-controlled oscillator circuit, and the output of the bandpass filter is applied to a comb filter placed outside the APC loop. It is possible to provide a color jitter correction circuit for a video disc playback device, which can have tracking characteristics and, as a result, can play back color signals with a high S/N ratio.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of a video signal system of a conventional video disc playback device. FIG. 2 is a schematic block diagram of an embodiment of the present invention. FIG. 3 shows the closed loop characteristics of the conventional APC loop shown in FIG. FIG. 4 shows the closed loop characteristics of the APC loop of the embodiment shown in FIG. In the figure, 1 is a disk signal pickup section, 2 is an F
'M detector, 3 is the first frequency conversion circuit, 4 is the bandpass filter, 5 is the first comb filter, 6 is the ACC circuit, 7
1 is a phase detection circuit, 8 is a voltage-controlled crystal oscillator circuit, 9 is a second frequency conversion circuit, 10 is a second comb filter, 1
1 is a control circuit, and 60 is a second ACC circuit.

Claims (1)

[Claims] (1) A color jitter correction circuit for a video disc playback device that removes jitter components of a color signal included in a playback video signal picked up from a video disc, the circuit being configured to remove jitter components from the video signal. The automatic phase control loop includes a frequency conversion circuit, a bandpass filter that passes the frequency band of the color signal, and an ACC.
circuit, a phase detection circuit, and a voltage-controlled oscillation circuit whose frequency changes in response to the output of the phase detection circuit; A color jitter correction circuit for a video disc playback device, comprising a comb filter that separates only color signal components from the video signal from which the color jitter has been removed.