JPS614390A - Chrominance signal modulating and demodulating system - Google Patents

Abstract

PURPOSE:To correct the synchronous state in a short time and to simplify the circuit by using a horizontal synchronizing signal as synchronizing signals of a demodulating circuit and a modulating circuit that performs demodulation and modulation. CONSTITUTION:In this system, a horizontal synchronizing signal is used as a synchronizing signal supplied to the load terminal LD of a counter 1, and a signal from output QB of duble period is supplied to a preset terminal B of the second bit from the low order. When a horizontal synchronizing signal is set as a synchronizing signal, the next pulse shown by a solid line in the figure D becomes as shown by a dotted line. Accordingly, it becomes necessary to make output of QB to opposite phase at the beginning of 1 line. Therefore, it is so designed to supply ''1'' to a low-order bit of the preset terminal and to supply a signal from the output QB of double period to the preset terminal B of the second bit from low-order. That is, even when a horizontal synchronizing signal is made to a synchronizing signal, demodulation of chrominance signals and modulation of demodulated chrominance signals can be realized by the circuit shown in the figure.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical field of the invention The present invention is directed to the NTSC (National Televis
Regarding the digital modulation and demodulation processing of the color signal of the TV signal of the ionS7gtem Corrml ttae) standard, the color signal is converted to the color subcarrier frequency (hereinafter referred to as FTRA).
This invention relates to an improvement in a processing method that digitally demodulates a signal sampled at a sampling frequency four times as high as , and then modulates and restores the transmitted or recorded material.

o)) Technical Background In order to digitally process the color signal quadrature-modulated at f8c in the NTSC standard TV signal, the color signal C(nr) sampled at a sampling period T of 1/4 fsc is (
1) It is shown by the formula.

C(nt) = (Anw(2π4T nT)+Bng
ln(2πfy nT) )·(t) However, AnBn corresponds to the I and Q components of the color signal, and n is an integer from 0 indicating the sampling order of the sampling points.

To obtain An and Bn by demodulation from equation (1), as is well known, use equation (1) as the coefficient = (Qll(2π-4T ”)
It can be found by multiplying by +s stone (2π "nT)".

That is, the equation for this demodulation is as shown in equation (2).

CD(aT)=C(nt)xK=(Ancm(zπtechn
r) 4-ten Bn*(11π-;nr))
T) +gln(2πT-n'r))
... Song...(2) That is, in equation (2), when n is an even number, it becomes An, and when n is an odd number, it becomes Bn, and demodulated An and Bn can be obtained.

This means that the value of the coefficient in equation (2) is 0.1.2.
When it becomes 3゜4, 5.6.7...1. i, -1
, -1, 1, 1, -1, -1... so C
The value of (nr) is 0.1.2.3.4.5°6.7.
When...1.1. -1. -1.1.1. -1. -1...
・That is, 1/4 fsc = 4 of T
1 of double period. All you have to do is extract the value multiplied by -1.

It is demodulated in this way, and if n is an even number, it becomes An,
When n is an odd number, the signal Bn can be modulated as in the original equation (1) by multiplying it by a coefficient K as shown in the following equation (3).

(An10Bn) When n is an even number, it is 1 and when it is an odd number, it is O, and dn (2π work nr) is O when n is an even number and 1 when it is an odd number, so equation (3) is A
nw (2shi^1r) + Bnm (zg - 5nT) (
1) It becomes the same as Eq.

This means that when n becomes 0.1.2.3.4.5.6.7... as in the case of the postverb in (AntenBn),
1.1. -1゜-1, 1, 1, -1, -1...
< 1/4 f
ttrc = 1.4 times the period of T. 0 (a) Prior art and problems A conventional circuit for demodulating and modulating a sampled color signal has the first factor and the second factor in Figure 2. I will explain using In this case, the demodulation circuit and modulation circuit may be the same. FIG. 1 shows a diagram of a conventional demodulation circuit and modulation circuit.

FIG. 2 shows the waveforms of each part in FIG. A pulse with a period twice that of the vertical synchronizing pulse is supplied as a synchronizing signal, and any signal can be supplied to preset terminals A and B, but in Fig. 2 it is 1110''. As a four-piece T, as shown in Figure 2
= A clock with a period of 1/4 fma is supplied, and the output QB with a period twice as high as T =
A pulse with a period four times that of 1/4 f sc is emitted,
When the output from QB, which is supplied to the selection terminal S of the selector 2 and shown in FIG. 2 (2), is at L level, a signal obtained by multiplying the color signal by -1 in the multiplier 4 is output when demodulating. In the case of modulation, a signal obtained by multiplying the demodulated color signal by -1 in the same multiplier 4 is selected to be output. When the output of QB is at H level, when demodulating, the multiplier 3 selects a signal that is multiplied by 1 to the chrominance signal, and when modulating, the demodulated chrominance signal is
Similarly, the multiplier 3 selects to output a signal multiplied by 1.

In this way, the color signal or the signal obtained by multiplying the demodulated color signal by 1 or -1 is selected every four times the cycle of 1/4 f sc = T, so the color signal is demodulated and demodulated. It is possible to modulate color signals.

However, in this method, the synchronization signal is a pulse with twice the period of the vertical synchronization signal, so this pulse is usually not used elsewhere and requires a new pulse generator, and the period is long, so it cannot be synchronized due to noise etc. In this case, there is a drawback that correction cannot be made between two frames.

(d) Purpose of the Invention In view of the above-mentioned drawbacks, the purpose of the present invention is to provide a synchronizing signal that demodulates a color signal and modulates the demodulated color signal, and which has a short period and is generally used for other signal processing. The purpose of the present invention is to provide a color signal modulation/demodulation method using pulses that are

(e) Structure of the Invention In order to achieve the above object, the present invention is configured using a horizontal synchronization signal as a synchronization signal for a demodulation circuit that demodulates a color signal and modulates the demodulated color signal, and a modulation circuit. .

That is, by using the horizontal synchronization signal, the period of the synchronization signal becomes shorter, and since the horizontal synchronization signal is usually used in devices that process some kind of TV double signal, there is no need to have a synchronization signal generator. , and can achieve a synchronized state in a short time.

(f) Embodiment of the Invention An embodiment of the invention will be described below with reference to the drawings. In this case as well, the demodulation circuit and modulation circuit are the same circuit.

The waveforms (A)-(Dl correspond to points a-d in FIG. 1).

The difference between Fig. 3 and Fig. 1 is that a horizontal synchronization signal is used as the synchronization signal supplied to the load terminal LD of the counter, and the signal from the output QB with double period is preset to the second bit from the lowest. This is because the signal is supplied to terminal B.

If the horizontal synchronization signal is used as a synchronization signal, synchronization is achieved for each line, but in the case of an NTSC standard TV signal, if the clock cycle is T W 1/4fsc, the sampling points for one line are 910, which is divisible by 2. is not divisible by 4, so at the point of loading the horizontal synchronizing signal, the solid line pulse is followed by the dotted line as shown in Figure 4 0, so at the beginning of one line, the QB output is loaded. It is necessary to make the phase opposite.For this reason, "1" is supplied to the lower bit of the preset terminal, and the signal from the output QB of twice the cycle is supplied to the preset terminal B, which is the second bit from the lower. Furthermore, since the demodulated color signal and the beginning of the frame when it is modulated are not synchronized, the modified color signal selected by selector 2 has a 180° phase with the original demodulated color signal. There may be cases where the values are different.

However, when processing color signals on a monitor, the colors are An, B.
Since it is determined by the power of n and the phase difference between An and Bn, even if the phase changes by 180°, there is no problem because the phase difference between An and Bn does not change.

The above was explained by supplying the output of 11" to preset terminal A and the output of QB to B, but this
A similar effect can be obtained by supplying II□II to B and supplying the inverted output of QB to B.

That is, even if the synchronization signal is used as a horizontal synchronization signal, the color signal can be demodulated;
Modulation of the demodulated color signal can be realized by the circuit shown in FIG.

In this way, since the period of the synchronization signal is short, even if synchronization breaks down, it can be corrected immediately. Furthermore, since the horizontal synchronization signal is normally used, there is no need to have a synchronization signal generator.

(g) Effects of the Invention As explained in detail above, according to the present invention, the period of the synchronization signal is short, so even if synchronization is lost due to noise, it can be corrected immediately.
In addition, there is an effect that there is no need to have a synchronization signal generator.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a demodulation circuit and modulation circuit of a conventional example, FIG. 2 is a time chart of waveforms of each part in FIG. 1, and FIG. 3 is a block diagram of a demodulation circuit and a modulation circuit of an embodiment of the present invention. FIG. 4 is a time chart of waveforms at various parts in FIG. 3. In the figure, 1 is a counter, 2 is a selector, 3 is a multiplier of 1,
4 indicates a -1 multiplier. τ Ding - Deki・

Claims (1)

[Claims] A demodulation circuit and a modulation circuit that perform demodulation and modulation in a processing method that digitally demodulates a signal obtained by sampling the color signal of an NTSC standard TV signal at a frequency four times that of the color subcarrier, then modulates it and returns it to its original state. A color signal modulation/demodulation method characterized by using a horizontal synchronization signal as a synchronization signal.