JPH0219096A - Color signal processing circuit - Google Patents

Abstract

PURPOSE:To reduce a residual jitter component by comparing the phase of an output signal of an APC circuit or that of an output signal of a phase adjustment circuit with the phase of a reference signal from a reference signal generating circuit so as to output a control signal thereby using the output of the phase adjustment circuit as a reproduced color signal output. CONSTITUTION:A reproduced low frequency conversion color signal CL incoming from a terminal 1 is converted into a high frequency by using a color signal CP at an APC circuit 2. Then the phase of the color burst of the signal CP and the phase of a reference signal fref from a reference signal generating circuit 4 are compared by a control signal generating circuit 5 to generate a control signal (a), the phase of the signal CP is adjusted minutely at a phase adjustment circuit 3 by using the control signal (a) and the result is outputted at an output terminal 9 as the signal C. Thus, the residual jitter component is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color signal processing circuit for a recording/reproducing apparatus using a low frequency converted color signal, such as a home VTR.

BACKGROUND ART Conventionally, in a home VTR, a color signal C is low-band converted to a frequency fL that has a predetermined relationship with the frequency f, □ of a horizontal synchronizing signal H of a video signal, resulting in a low-band converted color signal. F
It is mixed with the M-modulated luminance signal Y and recorded on a magnetic tape, and during reproduction, a reproduced color signal can be obtained by processing in the reverse manner.

Here, the VH3 method uses a phase shift method (PS method) that sets IL to 40 j n and performs 90° low clearance, and the β method and 8+nn+ method use I
It is well known that L is set to 43.15fl and 47.25fl+ and a phase invert method (PI method) is adopted in which phase inversion is performed. Here, a conventional VH3 type color signal processing circuit is shown in FIG. 5 and explained in detail.

During recording, an input color signal C having a frequency fc is inputted from a terminal 20, and is multiplied by a signal A in a main multiplier 8M21 to produce a signal. Here, the signal frequency fL
is 40 f u, approximately 629 KHz, and the frequency to the signal is 1. is ja-fc+fL, which is approximately 4.2 MHz. On the other hand, horizontal synchronization signal 1 (obtained from the input video signal,
The circuit for multiplying by
O) Consists of a 28.1/8 frequency divider and a 29.1/40 frequency divider 30. In this AFC circuit 26, 320IH
By dividing the output of VC02B which oscillates at 9
0゛ We are getting a rotary 40fH. Part 40
f n signal, input color burst and APC circuit 2
3 locked with 3, 58 MI [z is sub multiplier BM2
By multiplying by 2, signal A is obtained.

During playback, the main multiplier BM31 multiplies the playback signal with the frequency IL including the jitter component by the signal A (frequency ja - fc 10ft) including the jitter component, thereby producing a playback color without jitter components. A signal Cp is obtained. Here, the signal A is the reproduced color signal CP and the reference signal generation circuit X'
3,58MH2 reference signal f which is the output of te136
Based on the information obtained by comparing the phases of ref with the phase comparator PC33, the VCO 34 is controlled to obtain 320 f u, which is divided by 90 degrees in the 1/8 frequency divider circuit to become 40 j u, and that signal and f rof are subdivided. By multiplying by the multiplier BM32, jref+4OfH, that is, signal A is obtained. Here, this reproduction system circuit is a reproduction color signal Cp.
It is well known that the APC circuit 37 controls the color burst to have the same frequency and constant phase as f ref .

Problems to be Solved by the Invention However, in the configuration of the reproduction system of the above conventional example, the APC
In a circuit, it is practically impossible to make the gain infinite, and since there is a limit to the response speed, a jitter component always remains, degrading the PN value, which is the S/N ratio of the color signal. On the playback screen, so-called sideways noise was generated.

Means for Solving the Problems In order to solve the above problems, the present invention converts a color signal into a low frequency signal and reproduces a recording medium recorded as a low frequency converted color signal. an APC circuit that converts the converted color signal to a high frequency while removing jitter components;
a phase adjustment circuit that receives a reproduced color signal that is an output signal of the APC circuit and finely adjusts the phase of the reproduced color signal according to a control signal from a control circuit; and an output signal of the APC circuit, or an output of the phase adjustment circuit. The control circuit compares the phase of one of the signals with a reference signal from a reference signal generation circuit and outputs a control signal, and the output of the phase adjustment circuit is configured to output a reproduced color signal. be.

Operation The present invention, with the above-described configuration, can significantly reduce the residual jitter component that could not be removed by the conventional APC circuit, and is effective in improving the PM value and reducing horizontal scanning noise.

Embodiment A block diagram of a first embodiment of the present invention is shown in FIG. 1. A reproduced low frequency converted color signal CL inputted from a terminal 1 is converted into a color signal CP and a high frequency signal in an APC circuit 2. .

The control signal generation circuit 5 compares the color burst of the signal CP and the phase of the reference signal j ref from the reference signal generation circuit 4, generates a control signal a, and generates the signal CP from the control signal a.
After the phase is finely adjusted by the phase adjustment circuit 3, the output terminal 9
is output as signal C. Here, the APC circuit 2 is
It is the same as the APC circuit 37 of the conventional example shown in FIG. , and a jitter-free color signal can be obtained, but in reality, as mentioned earlier, due to the finite gain in the APC circuit and the responsiveness of the APC circuit, jitter components remain in the CP. be.

Here, the control signal generation circuit 5 includes a phase comparator PC6, a gate circuit Gate7, and a low pass filter LPFB. The gate circuit 7 inputs the horizontal synchronization signal H,
The gate is closed only during the burst period.

An example of the phase adjustment circuit 3 is composed of resistors R1, R2, R3, a capacitor C, a coil L, and a varicamp 10, as shown in FIG. This is to finely adjust the phase of the signal.

In addition to this, various other circuits having constant frequency characteristics and varying only the phase may be used. By optimally operating this phase adjustment circuit 3, the residual jitter of the signal CP can be significantly reduced.

Next, a second embodiment of the present invention is shown in FIG.

This differs from the first embodiment in that the input signal of the phase comparator PC6 of the control signal generation circuit 5 is input from the output of the phase adjustment circuit 3. This forms a closed-loop feedback control "B" in contrast to the oven loop control n of the first embodiment, and although the responsiveness is inferior to that of the first embodiment, the stability is improved.Each part The operation is similar to that of the first embodiment.

Next, a third embodiment of the present invention is shown in FIG. 4, in which the output information of the phase comparator PC33 existing in the conventional APC circuit 37 is used as a control signal as it is. This is one method that can be achieved at the lowest cost. The operation of each part is the same as in the first embodiment.

Effects of the Invention As described above, the present invention has the above-mentioned configuration.
The residual jitter component that could not be removed by the circuit can be significantly reduced, and it is effective in improving the PM value and reducing horizontal noise.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a circuit diagram of a phase adjustment circuit of the present invention, and FIG. 3 is a block diagram of a second embodiment of the present invention.
FIG. 4 is a block diagram of a third embodiment of the present invention, and FIG. 5 is a block diagram of a conventional example. 2.37...APC circuit, 3...phase! I! 1 adjustment circuit, 4... crystal oscillation circuit, 5...
... Control signal generation circuit, 6.33 ... Phase comparator, 7 ... Gate circuit, 8 ... Low pass filter, 31.32 ...・fil n
H. Name of agent: Patent attorney Shigetaka Awano (1 person) Figure 1

Claims (2)

[Claims] (1) In a playback device that converts a color signal to a low frequency band and plays back a recording medium recorded as a low frequency converted color signal, the reproduced low frequency converted color signal is converted to a high frequency band while removing jitter components. an APC circuit; a phase adjustment circuit that receives a reproduced color signal as an output signal of the APC circuit and finely adjusts the phase of the reproduced color signal according to a control signal from a control circuit; and an output signal of the APC circuit or the phase of the reproduced color signal; The control circuit is configured to compare the phase of one of the output signals of the adjustment circuit with a reference signal from the reference signal generation circuit and output a control signal, and the output of the phase adjustment circuit is used as a reproduced color signal output. Characteristic color signal processing circuit. (2) The color signal processing circuit according to claim (1), wherein the control signal is obtained from an APC circuit.