JPH0946721A - Phase correction device for pal system chrominance signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the phase distortion of PAL system chrominance signals in a digital circuit, to eliminate a subtractor and to reduce a circuit scale. SOLUTION: This device is composed of a demodulation part 10 for demodulating the PAL system chrominance signals EC to color difference signals EB- Y and ER- Y, a point sequential circuit 11 for making the color difference signals EB- Y and ER- Y point sequential, a phase correction part 12 for correcting the phase of point sequential signals and an interpolation circuit 13 for performing separation into the color difference signals EB- Y and ER- Y and they are all the digital circuits. The phase correction part 12 is composed of a 1H delay line 21 and an adder 22 and the 1H delay line 21 delays the point sequential signals for 1H.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase correction apparatus for correcting a phase distortion of a color signal generated in a transmission system in a PAL system in a color television, and more particularly to a digital circuit in which a phase correction circuit is arranged after a demodulation circuit. The present invention relates to a phase correction device for a PAL system color signal that can be realized.

[0002]

2. Description of the Related Art The PAL (Phase Alternation by Line) system in a color television used in Europe and the like uses RY and BY signals as color difference signals. At the time of transmission, the color subcarrier is amplitude-modulated by this color difference signal and multiplexed on the luminance signal. At this time, the phase of the color subcarrier of the RY signal is inverted by 180 degrees for each scanning line. By utilizing this feature, even if there is a phase shift of the color carrier, it can be corrected at the time of reception to reduce the image quality deterioration.

FIG. 2 shows a conventional phase correction apparatus for analog PAL color signals. This phase correction device includes a phase correction unit 30 and a demodulation unit 31. First, the color signal E _C1 is input to the phase correction unit 30, and one horizontal scanning period (hereinafter referred to as 1H)
1H delay line that delays the signal only (1H Delay Line) 3
Pass 2. The color signal E _C2 for the next scanning line is input,
The calculation with the color signal E _C1 is performed. That is, the color signals E _C1 and E _C2 are added by the adder 33 and subtracted by the subtractor 34 to remove the phase distortion of the color signal E _C.

Here, the correction of the phase distortion of the color difference signal will be described in detail. FIG. 3 shows a vector diagram of the color signals E _C1 and E _C2 , (A) shows the color signal E _C1 , and (B) shows the color signal E _C2 of the next scanning line. The color signals E _C1 and E _C2 are, respectively,
This is a combination of E _BY and E _RY of color difference signals that are 90 degrees out of phase with each other in the directions of the RY and B axes that are orthogonal to each other. The color difference signal _{ERY on the RY} axis of the color signals E _C1 and E _C2 is inverted by 180 degrees. Therefore, the addition of the color signals E _C1 and E _C2 results in 2E _BY , and the subtraction results in ± 2E _RY .

When the color signals E _C1 and E _C2 are subject to Δθ phase distortion in the transmission system, for example, as shown in FIG.
It changes to _C11 and E _C21 . As described above, in the color signal, the positive and negative signs of the phase distortion of Δθ are reversed every 1H. Therefore, the color difference signal on the B-Y axis → E _BY ± ΔE _BY The color difference signal on the R-Y axis → ± (E _RY ± ΔE _RY ) Therefore, as described above, the 1H delay line 32
The color signal delayed by H and the color signal of the next scanning line are added by the adder 33.
By adding / subtracting with the subtractor 34, ΔE _BY ΔE _RY is canceled and the phase distortion is corrected.

Next, the demodulation section 31 will be described. A reference subcarrier E is generated by the crystal oscillator 35 with reference to the burst signal B.
Generate _{S (RY)} . A 90-degree phase shift circuit 36 shifts the phase of this signal by 90 degrees to generate a reference subcarrier E _{S (BY)} .
Further, the reference subcarrier −ES _(RY) is created by 180 ° by the 180 ° phase shift circuit 37. The color difference signal E _BY is only positive and only needs to be multiplied by 90 degrees.
_{Since RY} has both positive and negative signs, it is necessary to switch between 0 and 180 degrees for demodulation in order to make it positive only. Therefore, the line discrimination signal f _H is divided by the flip-flop 38 to generate f _H / 2, and the selector 39 is used to switch the signal. These three reference subcarrier signals, + 2E _BY , ±
2E _RY and demodulate. Thus, PAL
Three types of reference subcarriers necessary for the color signal demodulation of the method are generated.

In the BY demodulation circuit 40, the signal + 2E _BY from the adder 33 and the signal E _{S (BY)} from the 90 ° phase shift circuit are provided.
To generate the color difference signal E _BY . RY demodulation circuit 41
Then, the signal from the subtractor 34 + 2E _RY and the selector 39
By a signal from the E _{S (RY),} or the signal -E S _(RY) from the signal -2E _RY and selector 39 from the subtractor 34, and generates the color difference signals E _RY.

[0008]

If the above-mentioned analog circuit configuration is used and digitization is attempted for reasons such as image quality improvement, a problem occurs in the 1H delay line portion.
That is, in the PAL system, the horizontal scanning line period T _H = 64 μ
Let s be the frequency of the reference subcarrier f _SC = 4.4336187
Assuming 5 MHz, the time T _D delayed by the 1H delay line is T _D = 1 / f _SC × (283 + 1/2) = 63.943 μ
s the <T _H. In order to convert it into a digital signal, it is necessary to perform sampling at f _SC , but it is difficult to convert a half portion of the signal into a digital signal.

An object of the present invention is to provide a PAL system color signal phase correction demodulation circuit capable of converting the phase distortion of the PAL system color signal into a digital circuit.

[0010]

A first invention is a demodulation circuit for demodulating a PAL color signal into a color difference signal using a reference subcarrier, and a phase for correcting phase distortion of a signal output from the demodulation circuit. A correction circuit is provided, and the phase correction circuit includes a delay unit that delays the color difference signal by one horizontal scanning period in synchronization with the reference subcarrier, and an addition unit that adds the color difference signal and the delay signal. P characterized by
This is an AL system color signal phase correction device.

A second invention is a demodulation circuit for demodulating a PAL system color signal into a plurality of color difference signals by using a reference subcarrier, a single signal conversion circuit for integrating the color difference signals into a single signal, and the single signal conversion circuit. A phase correction circuit that corrects the phase distortion of the signal, and a separation circuit that separates the signal output from the phase correction circuit into a color difference signal, the phase correction circuit synchronizes the single signal with the reference subcarrier. The PAL system color signal phase correction apparatus is characterized in that it comprises a delay means for delaying only one horizontal scanning period and an adding means for adding the combined signal and the delayed signal.

A third invention is the PA according to the second invention.
In the L-system color signal phase correction device, the single signal conversion circuit is a circuit that sequentially arranges the color difference signals alternately in a constant cycle to perform dot sequential processing, and the separation circuit arranges the dot sequential signals from the dot sequential signal in constant cycles. It is characterized in that it is a circuit for extracting a color difference signal and separating it into color difference signals.

In the present invention, the phase distortion correction, which was previously performed in the analog system, is performed after the color signal demodulation. At the demodulation stage, the color signal is synchronized with the reference subcarrier signal, and one horizontal scanning period becomes an integral multiple of the reference subcarrier frequency. Therefore, the 1H delay line can be synchronized with the reference subcarrier frequency to realize a digital circuit. Further, since the signal after the color signal demodulation is only positive, the adder can perform the operation and the subtractor can be reduced. Particularly, in the second and third aspects, since the color difference signals are integrated into one after the color signal demodulation, the phase distortion can be corrected with one 1H delay line and one adder.

[0014]

1 is a block diagram showing an embodiment of a PAL type color signal phase correction apparatus according to the present invention. This phase correction apparatus includes a demodulation unit 10 for demodulating a PAL color signal E _C into color difference signals E _BY and E _RY , and a color difference signal E.
_{It is composed} of a dot-sequential circuit 11 for making the _BY and _ERY dot-sequential, a phase correction unit 12 for performing the phase correction of the dot-sequential signal, and an interpolation circuit 13 for separating the color difference signals _EBY , _ERY , all of which are digital circuits. is there.

The color signal E _C and the burst signal B, which are digital signals by an A / D converter or the like, are input to the demodulation section 10. First, the reference subcarrier E _{S (RY)} is created by the crystal oscillator 14 with reference to the burst signal B, and the 90 ° phase shift circuit 1
The reference carrier wave E _{S (BY)} is generated by shifting the phase by 90 degrees at 5
The phase shift circuit 16 shifts the phase 180 degrees, and the reference carrier wave-E
Generate _{S (RY)} . A signal for switching between ± _{ES (RY)} is required for _RY demodulation. Therefore, the line discrimination signal f _H is divided by the flip-flop 17 to generate f _H / 2, which is input to the selector 18 and the reference carrier ± _{ES (RY).}
2 signals are switched. E and _{S (BY),} put color signal E _C in BY demodulation circuit 19 to obtain a color difference signal E _BY.
The ± E _{S (RY)} and the color signal E _C are input to the _RY demodulation circuit 11 to obtain the color difference signal E _RY . At this stage, the color difference signal E
_BY and _ERY include phase distortion.

Next, the color difference signals E _BY and E _RY are applied to the dot sequential circuit 1
1 to make a dot sequence. With a frequency clock of f _SC / 2,
The function of the dot-sequential circuit 11 is to alternately take in the color difference signals E _BY and E _RY in a constant cycle and integrate them into one signal. This signal is input to the phase correction unit 12.

The phase corrector 12 comprises a 1H delay line 21 and an adder 22. The 1H delay line 21 delays the dot-sequential signal by 1H. The dot-sequential signal including the color difference signals E _BY and E _RY is synchronized with the frequency of the reference subcarrier, and the 1H delay line 21 is synchronized with the frequency of the reference subcarrier. Therefore, unlike the conventional technique, the signal delayed by 1H is
Sampling at f _SC is possible and there is no problem in digitization. The delayed signal and the dot-sequential signal are added by the adder 22. Since 1 signal is generated by the dot sequential circuit 11, 1H
Only one delay circuit 21 and one adder 22 are required. Since the demodulated chrominance signals E _BY and E _RY both have positive phases and the phase distortion is inverted between positive and negative every 1H, the phase distortion is removed by adding the chrominance signals E _BY as in the prior art. can do. Therefore, since it is not necessary to use a subtractor having a large circuit scale, the circuit scale of the phase correction unit 12 can be reduced, the overall size of the device can be reduced, and the cost can be reduced.

Finally, the dot-sequential signal is input to the interpolation circuit 20 and separated into two color difference signals E _BY and E _RY . The dot-sequential circuit with the phase distortion corrected has a color difference signal E for each f _SC / 2.
_BY and E _RY alternate. This signal is f _SC / 2
And the color difference signals E _BY and E _RY are separated.

The present invention is not limited to such a configuration. A phase correction circuit may be provided for each color difference signal without using the dot sequential circuit.

[0020]

According to the present invention, the phase distortion can be corrected into a digital circuit by the phase correction by the means for delaying one horizontal scanning period after demodulation. Moreover, since the phase of the color difference signal becomes positive by demodulation, the phase distortion can be eliminated by adding, and it is not necessary to use a subtractor having a large circuit scale, so that the circuit scale can be reduced. Furthermore, the demodulated signal is set to 1
In this case, since the phase correction circuit requires only one delay unit and one addition unit, it is possible to provide a small and inexpensive device.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a PAL system color signal phase correction apparatus according to the present invention.

FIG. 2 is a block diagram showing an example of a conventional PAL system color signal phase correction apparatus.

3A and 3B are vector diagrams of color signals generated by a conventional PAL system color signal phase correction apparatus.

[Explanation of symbols]

 10 Demodulator 11 Point Sequential Circuit 12 Phase Corrector 13 Interpolator 21 1H Delay Line 22 Adder

Claims (3)

[Claims] 1. A phase correction circuit comprising: a demodulation circuit for demodulating a PAL color signal into a color difference signal using a reference subcarrier; and a phase correction circuit for correcting phase distortion of a signal output from the demodulation circuit. A delay means for delaying the color difference signal by one horizontal scanning period in synchronization with the reference subcarrier;
A phase correction apparatus for a PAL system color signal, comprising: an addition unit that adds the color difference signal and the delay signal. 2. A demodulation circuit for demodulating a PAL system color signal into a plurality of color difference signals using a reference subcarrier, a single signal conversion circuit for integrating the color difference signals into one signal, and phase distortion of the single signal. And a separation circuit that separates the signal output from the phase correction circuit into color difference signals again. The phase correction circuit synchronizes the single signal with the reference subcarrier for one horizontal scanning. Delay means to delay by a period,
A phase correction apparatus for a PAL system color signal, comprising: an addition means for adding the combined signal and the delayed signal. 3. A single signal conversion circuit is a circuit for arranging each color difference signal alternately in a constant cycle and performing dot sequence, and a separation circuit extracts a color difference signal arranged in a constant cycle from the point sequential signal. 3. The phase correction apparatus for PAL color signals according to claim 2, wherein the circuit is a circuit that separates each color difference signal.