JPS5932954B2 - demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a demodulating device for a PAL carrier color signal.

Conventionally, a demodulator for a PAL carrier color signal is (B-Y)
It consisted of a synchronous detector on the axis, a synchronous detector on the (RY) axis, a comb filter, and a polarity inversion circuit for the (RY) demodulated component, but compared to the NTSC system, , there was a problem that it had many components and was complex.

The present invention seeks to solve the above-mentioned problems.

Hereinafter, the present invention will be explained based on illustrated embodiments. FIG. 1 is a block diagram of essential parts of an embodiment of the present invention.

In the figure, the carrier color signal supplied to the signal input terminal 1 and the (B-Y
) A detection carrier wave (carrier) ΦC having a phase difference of 450 with respect to the synchronous detector 3 is input to the synchronous detector 3.

The output signal of this synchronous detector 3 is supplied to a 1H delay line 4, an adder 5 and a subtracter 6. Those IH delay lines 4,
The adder 5 and the subtracter 6 constitute two sets of complementary comb filters 10. The two output signals of this comb filter 10, that is, the output signal of the adder 5 are (B-Y)
The output signal of the subtracter 6 is supplied to the (RY) component output terminal 9 via a polarity inversion circuit T. An example of the spectrum of the carrier color signal supplied to the signal input terminal 1 is shown in FIG.

The spectrum shown in the figure is fs=(284-T)fH
+25H2 (where fH is the horizontal scanning frequency) is the (B-Y) component shown by the solid line, and the (R-Y) component shown by the broken line.
It consists of a spectrum of components. The spectrum of each component is divided into two orthogonal axes as shown in Figure 3 (
Since quadrature two-phase modulation is performed on the B-Y) axis and the R-Y axis, each has orthogonal phase terms.

When such a carrier color signal is detected by a detection carrier wave Φc having a phase of +450 with respect to the (BY) axis, a demodulated output having a spectrum as shown in FIG. 4 is obtained. In this type of uniaxial demodulation with one detection axis, the detection carrier wave Φ
This is achieved by setting the phase of c to 45 with respect to the (BY) axis. Of the demodulated output signal, the (B-Y) component is extracted by a comb filter constituted by a 1H delay line 4 and an adder 5, as shown in its spectrum in FIG. On the other hand, the (R-Y) component whose polarity is inverted for each line is processed by the 1H delay line 4 and subtracter 6 and supplied to the polarity inversion circuit 7, as shown in the spectrum in FIG. be done.

In the polarity inversion circuit 7, the polarity is inverted line by line, thereby obtaining a normal polarity (RY) component having a spectrum as shown in FIG. As described above, by using 45 detection axes, only one synchronous filter is required, and the configuration of the carrier color signal demodulation device is simplified. In addition, in the embodiment of the present invention described above (
A demodulation axis of +45 with respect to the B-Y) axis was selected, but in addition, +135, 225, or 315, that is,
A similar effect can be obtained by selecting 453×n (where n is 3, 5, or 7). Further, if the signal transmission system includes a differential phase error, the phase of the demodulation axis may be shifted from +45 degrees depending on the value of the differential phase error.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a main part of an embodiment of the present invention, FIG. 2 is a diagram showing an example of the frequency spectrum of a carrier color signal, and FIG.
Figures 4 and 5 are diagrams showing the phase of the demodulation axis according to the present invention.
6 and 7 are diagrams showing examples of changes in the frequency spectrum. 3...Synchronous detector, 4...1H delay line, 5...Adder, 6...Subtractor, 7.
...Polarity inversion circuit, 10...Comb filter.

Claims (1)

[Claims] 1. A synchronous detector into which a PAL carrier color signal is input;
A comb filter separates the output of the synchronous detector into a (B-Y) component and a (R-Y) component whose polarity is inverted for each line, and a comb filter that normalizes the polarity of the (R-Y) component. A demodulator for a PAL carrier color signal is configured including a polarity reversal circuit that returns the polarity to 45°×n (however, , n is an integer of 1, 3, 5, or 7). 2. Claim 1 provides that, when a signal transmission system includes a differential phase error, the phase of the detection carrier wave is shifted from the specific angle according to the value of the differential phase error. A demodulating device characterized by comprising: