JPH0220991A - Color difference signal demodulator - Google Patents

Abstract

PURPOSE:To obtain a small-sized circuit of simple constitution by detecting the carrier color difference signal from a separating circuit synchronously with a digital chrominance subcarrier recovered by a chrominance subscriber recovery circuit and demodulating a color difference signal. CONSTITUTION:A composite color television signal tv is converted by an A/D converting circuit 52 into a digital signal with a sampling clock CLK to obtain a digital composite color television signal TV. This composite color television signal TV is separated by the separating circuit 55 into a luminance signal Y' and the carrier color difference signal Ec. A color burst signal, on the hand, is extracted by a chrominance subcarrier recovery circuit 53 to recover the chrominance subcarrier. The carrier color difference signal Ec is detected synchronously by a synchronous detecting circuit 55 with the chrominance subcarrier and color difference signals C1 and C2 are demodulated by digital processing. Consequently, the stability of the circuit is improved and adjustment is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Regarding a color difference signal set for demodulating color difference signals from a composite color television signal digitized with a sampling clock that is not an integer multiple of the frequency of a color subcarrier.

The purpose of this invention is to realize a circuit with a small and simple configuration that demodulates color difference signals from a composite color television signal by digital signal processing while using a sampling frequency that is not an integral multiple of the color subcarrier.

a sampling clock generation circuit that generates a sampling clock;
An A/D conversion circuit that A/D converts the composite color television signal using the sampling clock, and a digital color sub-circuit that extracts a color burst signal from the digital composite color television signal and synchronizes with it! A color subcarrier regeneration circuit that regenerates the cross-transmission wave, a separation circuit that separates the luminance signal and carrier color difference signal from the 3-digital composite color television signal, and a color subcarrier regeneration circuit that reproduces the general transmission color difference signal from the 9-separation circuit. and a synchronous detection circuit that performs synchronous detection and demodulates a color difference signal by digital color printing till transmission.

[Industrial application field]

The present invention relates to a color difference signal demodulator that demodulates a color difference signal from a composite color television signal, and more particularly to a color difference signal demodulator that demodulates a color difference signal from a composite color television signal digitized with a sampling clock that is not an integral multiple of a color subcarrier. Relating to signal demodulators.

Currently, the digitization of color television signals is progressing, and in preparation for international standardization, the CCIR (Consultative Committee International on Radio) supports the two current television systems (NTSC system and PAL system) as a sampling clock. It is recommended that 13.5 Mllz be possible. therefore,
There is a need to develop a demodulation circuit that can accommodate such a sampling clock of 13.5 M Ilz.

[Prior Art] When a color television signal is digitally processed, it is necessary to extract a luminance signal and a color difference signal of the digital signal from the composite color television signal.

There are two methods for this demodulation:

One is the method shown in FIG. 4 in which the luminance signal and color difference signal are separated by a digital circuit. In Figure 4, 31
32 is an A/D conversion circuit that converts the NTSC composite color television signal [V] from analog to digital; 32 is a color burst gate circuit that extracts the color burst signal CB (color subcarrier f sc) from the composite color television signal; 33
is the sampling clock (
34 is a comb filter that separates the luminance signal Y' and the carrier color difference signal EC from the digitized composite color television signal TV; 35 is a comb filter that divides the 4fsc sampling clock into 4; a frequency dividing circuit that generates a color subcarrier rsc with a frequency of 1/4;
is a delay circuit that delays the color subcarrier fsc from the frequency dividing circuit 35 by π/2, and 37 and 38 are digital carrier color difference signals C.
Multipliers 39 to 41 are low-pass filters for multiplying by +1.0°1.

In this demodulation method, a composite color television signal TV converted into a digital signal by an A/D conversion circuit 31 is separated by digital processing into a luminance signal Y' and a carrier color difference signal Ec by a comb filter 34, and the separated digital signal Multiplier 3 multiplies carrier color difference signal Ec by analog color subcarrier fsc.
7. Synchronous detection is performed at 38 to generate two digital color difference signals (B
-Y).

(T?-Y) is demodulated.

The other method is to separate the luminance signal and color difference signal using an analog circuit, and as shown in FIG.
1 separates the luminance signal Y and two color difference signals (B-Y) and (RY) through analog processing, and then converts these three signals into analog/digital signals using A/D conversion circuits 22 to 24, respectively.
Digital data is obtained through digital conversion.

[Problem to be solved by the invention]

In the former method, in which the luminance signal Y and two color difference signals are demodulated by a digital circuit, the frequency of the sampling signal Y is C
If the frequency is 13.5 Mllz according to the CIR recommendations, this frequency of 13.5 Mllz is not an integral multiple of the color subcarrier (frequency is approximately 3.579 MHz), so the color subcarrier required for coherent detection is A circuit that generates a signal whose phase is delayed by π/2 from the carrier wave cannot be easily realized using the delay circuit 36, which simply delays the Kugata signal by one clock. It is difficult to demodulate color difference signals from a digital composite color television signal with a sampling frequency of 13.5 Mllz.

On the other hand, the latter method in which the luminance signal Y and two color difference signals are filtered by an analog circuit requires a total of three A/D conversion circuits to convert these three signals from analog to digital after demodulation, which is uneconomical. At the same time, the equipment is becoming larger.

Furthermore, since it is an analog process, it has poor stability against temperature changes, changes over time, etc., and the adjustment method is also complicated.

Therefore, an object of the present invention is to be able to demodulate a color difference signal from a composite color television signal by digital signal processing while using a sampling frequency that is not an integral multiple of one color subcarrier. An object of the present invention is to provide a color difference signal demodulator having a small size and simple configuration.

[Means to solve problems]

FIG. 1 is a principle block diagram according to the present invention.

The color difference signal demodulator according to the present invention includes a sampling clock generation circuit 51 that generates a sampling clock, and an A/D conversion circuit 52 that converts a composite color television signal tv from an analog signal to a digital signal using a sampling clock CLX. , A/D
Composite color television signal T digitized by conversion circuit
A color subcarrier regeneration circuit 53 extracts a color burst signal CB in V and regenerates a digital color subcarrier synchronized therewith, and a luminance signal Y' is generated from a composite color television signal TV digitized by an A/D conversion circuit 52. a separation circuit 54 that separates the carrier color difference signal EC from the carrier color difference signal EC; and a synchronous detection circuit that synchronously detects the carrier color difference signal Ec from the 1 separation circuit 54 using the digital color subcarrier regenerated by the color subcarrier regeneration circuit and demodulates the color difference signal. 55.

[Effect]

The composite color television signal tv is converted into a digital signal by the A/D conversion circuit 52 using the sampling clock CLK to obtain a digital composite color television signal TV. This composite color television signal TV is divided into a luminance signal Y' by a separation circuit 55.
and the carrier color difference signal Ec. Here, the carrier color difference signal is a signal obtained by multiplexing two color difference signals C1+C2 using a color subcarrier by quadrature modulation.

On the other hand, a nine-color subcarrier reproducing circuit 53 extracts the color burst signal and reproduces the color subcarrier. Using this color subcarrier, the carrier color difference signal Ec is synchronously detected by a synchronous detection circuit 55, and the color difference signals C1+C2 are demodulated by digital processing.

The method of synchronous detection is to create a chrominance subcarrier and a chrominance subcarrier whose phase is shifted by π/2 from this by digital signal processing, and perform orthogonal synchronous detection of the carrier color difference signal Ec using these two chrominance subcarriers. .

〔Example〕

The present invention will be described in detail below with reference to one drawing. Second
The figure is a block diagram showing a color difference signal demodulator as an embodiment of the present invention.

In FIG. 2, an NTSC analog composite color television signal tv is clamped by a clamp circuit 1 and a DC component is regenerated, and then input to a horizontal synchronization detection circuit 2 and an A/D conversion circuit 4. The horizontal synchronization detection circuit 2 is a circuit that detects a horizontal synchronization signal in the composite color television signal tv and generates a detection pulse of a horizontal synchronization interval, and the detection pulse is input to the phase synchronization oscillator 3.

The phase synchronization oscillator 3 generates 13°5Ml1z which is phase synchronized with the horizontal synchronization signal based on the detection pulse of this horizontal synchronization interval.
This circuit generates a sampling clock fs-ρ of 858 sampling points even when the horizontal synchronization interval of a composite color television signal varies even if the horizontal synchronization interval is varied. These 858 sampling points are 13.5 MH under normal conditions with no fluctuation in horizontal synchronization interval.
It corresponds to z.

The A/D conversion circuit 4 converts the analog composite color television signal tv into a digital composite color television signal TV using the sampling clock r sap from the phase synchronized oscillator 3, and inputs it to the comb filter 5.

A comb filter 5 separates a luminance signal Y' and a carrier color difference signal Ec from this composite color television signal TV. The luminance signal Y' is converted into a luminance signal Y through a low-pass filter 12.

The carrier color difference signal EC is also input to the color burst gate circuit 6 and multipliers 10 and 11.

The color burst gate circuit 6 receives a composite color television signal T.
This circuit extracts only the color burst signal CB, that is, the color subcarrier S in V. Here, this color subcarrier S is
Let Eo be the maximum amplitude value of the color subcarrier and ωS be the angular frequency of the color subcarrier.

S = E□ 5in (ωs t) It is expressed as

The extracted color subcarrier S is the amplitude detection time i? 37 and multiplier 8. The amplitude detection circuit 7 is composed of a delay element 71 that provides a delay of one sample clock and a ROM 72, and the amplitude detection circuit 7 is composed of a delay element 71 that provides a delay of one sample clock, and a ROM 72, and the amplitude detection circuit 7 is composed of a delay element 71 that provides a delay of one sample clock, and a ROM 72.
Eo is calculated and given to the multiplier 8. The amplitude detection circuit 7 and the multiplier 8 constitute an amplitude adjustment circuit that adjusts the amplitude of the extracted color subcarrier S to a constant value.

The color subcarrier NS of constant amplitude output from the multiplier 8 is s
The signal is input to the in/cos conversion circuit 9. This Sin/c
The os conversion circuit 9 converts the color subcarrier N S -5in (ωs
t ) into a color subcarrier N C = cos (ωs t) consisting of a cosine wave whose phase is shifted by 90 degrees.
The color subcarrier NS is sent to a multiplier 10 and the one color subcarrier NC is sent to a multiplier 11.

A detailed configuration example of the sin/cos conversion circuit 9 is shown in FIG. In FIG. 3, 91 is a delay element, 92.95
~98 is a multiplier, and 93.94 is a selector.

99 is an adder, and 90 is a subtracter. Each multiplier 92.9
5 to 98 are circuits for multiplying the input signal by the coefficient in each block. Selectors 93 and 94 select the input side only during the color burst signal period.

In other periods, the input a side is selected, so that the color subcarrier extracted from the color burst signal CB can be sent to the multiplier 10.11 even in periods other than the color burst period. ing.

Multipliers 10 and 11 synchronously detect the carrier color difference signal EC from the comb filter 5 with the color print IN transmission waves NS and NC'. The respective detection outputs are demodulated into color difference signals (B-Y) (R-Y) by passing through low-pass filters 13 and I4.

The operation of the circuit of this embodiment will be explained below. The horizontal synchronization detection circuit 2 detects the horizontal synchronization signal and based on it, 13.
A sampling clock fss+p of 5 Mllz is generated by the phase synchronized oscillator 3. This sampling clock f sap
A/D conversion circuit 4 converts the composite color television signal tv using
digitized into a digital composite color television signal T
V is output to the comb filter 5.

The comb filter 5 separates this digital composite color television signal TV into a luminance signal Y' and a one-stop color difference signal EC, and outputs the separated signals. This carrier color difference signal Ec is supplied to multipliers 10 and 11.
It is also sent to the color burst gate circuit 6. Color burst gate circuit 6 extracts color burst signal CB from this carrier color difference signal Ec only during the color burst signal period, and sends it to amplitude detection circuit 7 and multiplier 8.

Here, in order to demodulate the two color difference signals (R-Y) and (B-Y) from the carrier color difference signal Ec by synchronous detection, the color subcarrier S extracted from the color burst signal CB is added to the carrier color difference signal Ec. The multiplier 10.11 multiplies the signal by the color subcarrier C whose phase is shifted by 90 degrees, and then passes the signal through the low-pass filters 13 and 14, respectively.

That is, if the amplitudes of the two color difference signals (R-Y) and (B-Y) are respectively Er and Eb, then the m feeding color difference signal Ec is.

Ec = Er cos(ωs t) + Eb 5in
(ωs t). In order to extract the amplitudes Er and Eb of the color difference signals from this II color difference signal Ec, it is necessary to
C has a color subcarrier S = EO5in (ωs t ) and a color subcarrier C = Eo C whose color phase is shifted by 90°.
03 ((1) S t ). Namely.

Ec X Eo 5in(ωs t) =F, o 5
in(ωs t)X (Er cos(ωs t)
+Eb 5in(ωst) )='AEb F, o
+'AEr Eo 5in (2ωs t)++AE
b Eo C03(2(IIs t)Ec XEa
cos(ωs t) =Eo cos(ωs
t)X (Er cos(ωs L) +Eb
5in(ωs t) )='AEr Eo +! 4
Eb Eo 5in (2ωs L) 10'AEr Eo
cos(2ωs t). This (2) and (
If the signal obtained by the 3-channel equation is passed through the low-pass filter 13.14 to remove the second harmonic, the term (2ωs t) disappears, and 〃Eb Eo + %Er Eo is obtained. baseband color difference signal (RY),
(B-Y) is found.

However, in this case, one color difference signal (RY), (B-Y)
is the maximum amplitude value E of the color subcarrier S. If the value changes, the size will change accordingly. Therefore, in this embodiment, the amplitude of the color subcarrier used for synchronous detection is adjusted to a constant value by an amplitude adjustment circuit comprising an amplitude detection circuit 7 and a multiplier 8.

That is, the amplitude detection circuit 7 detects the maximum amplitude value E of the color subcarrier S.
o is detected and its inverse value 1/E is given to the multiplier 8, and the multiplier 8 converts the color subcarrier S = E□ 5in(ωs t
), the amplitude-adjusted color subcarrier etN
Create S=sin(ωs L) and convert it into sin/co
The signal is supplied to multipliers 10 and 11 for synchronous detection via an s conversion circuit 9.

Here, the amplitude detection circuit 7 detects the maximum amplitude value E of the color subcarrier S.

, two consecutive sample time points to.

It is obtained from the sampling data of Ll. That is,
At the sampling point, the color subcarrier data sampled at 3
1+ The previous sample time t.

The color subcarrier data sampled in S. If so.

The color subcarrier data So is.

S□ = EO5in (ωs tq ) = Eqsin (ωs L1$), where φ is the phase difference between the sampling time to and tl, and when the 9 color subcarriers are sampled at a sampling frequency of 13.5MHz. It is approximately 95.4545 degrees. If we further transform the color subcarrier data So in equation (4) above.

5o=Eosin(ωs El −φ)=Eosin
(ω5L1)cosφ−EOcos(ω5at)sinφ=Sj cosφ−Eocos(ω5L1)sinφ. Therefore.

,', (SO-31cosφ)2-(F, □ cos(ωs t 1 ) sinφ)]2 where.

Eo 2-CEO5in(ωs tl ) )
From the relationship 2+(EOCO3(ω5L1))2.

(So-3, cosφ)2 -(lEo 2-3t 2) sin 2φ・-(5) Therefore, the amplitude Eo is two consecutive sample data S.

+31 and the constant 5irlφ+cosφ. The amplitude detection circuit 7 in FIG. 2 performs this calculation to find the maximum amplitude E, and its reciprocal value 1 / E
This circuit outputs two consecutive sample data So and S1 using a delay element 71, and uses this as an address to read data of 1/Eo from the ROM 72 and output it. Here the maximum swing l1gEo
Since the value of does not change frequently, it is sufficient to output it once based on the color burst signal for each scanning line, and the ROM?
2 can be realized with EPROM.

This I/E o and color subcarrier S = E□ 5in
((ds t ) is multiplied by the multiplier 8 to obtain a color subcarrier N S =sin(ωs t ) with a constant amplitude,
Based on this 5in(ωs L), s in/cos
Cos (ω!1) with a 90 degree phase shift in the conversion circuit 9
t). And these amplitude-constant color subcarriers 5
Using in(ωst) and cos(ωs L), the carrier color difference signal Ec is synchronously detected in a multiplier 10.11 to obtain one color difference signal (B-Y) and (R-Y).

Various modifications are possible in implementing the invention. Although the above-mentioned embodiment applies the present invention to an NTSC color television signal, the present invention is not limited thereto.
It can also be used for AL color television signals.

〔Effect of the invention〕

According to the present invention, it becomes possible to sample a color television signal using a sampling clock that is not an integer multiple of the two-color subcarrier and demodulate a color difference signal through digital signal processing. In this case, since the color difference signal is obtained by directly converting the color television signal from analog to digital and performing digital signal processing, a luminance/color difference signal separation circuit using an analog circuit is not used, and therefore the stability of the circuit is improved. This has improved the performance and simplified the adjustment.

The number of A/D conversion circuits used can be reduced compared to the analog type, and the circuit can be made smaller by using LSI.

[Brief explanation of the drawing]

FIG. 1 is a principle block diagram according to the present invention. FIG. 2 is a block diagram showing a color difference signal demodulator as an embodiment of the present invention. FIG. 3 is a block diagram showing an example of the configuration of the sin/cos conversion circuit in FIG. 2. FIG. 4 is a block diagram showing a conventional digital color difference signal demodulator; FIG. 5 is a block diagram showing conventional analog color difference signal demodulation. In fig. 1-clamp circuit 2-horizontal synchronization detection circuit 3.33...phase synchronization oscillator 4.31--A/D conversion circuit 6.32-color burst gate circuit 5.34..., comb filter 7-・Amplitude detection circuit 8.10, 11, 37.38--Multiplier 9...a
in/cos conversion circuits 12-14.39-41--Low-pass filter 91--Delay element 93.94--Selector 92.95-98--Multiplier 99--Adder 9〇-Subtractor Non-explosion date/month 1z4 system principle block diagram Figure 1 SIN/CO9Lm times h tn configuration g e11 Figure 3

Claims (1)

[Claims] A sampling clock generation circuit (5) that generates a sampling clock.
1), and an A/D conversion circuit (52) that converts the composite color television signal from an analog signal to a digital signal using the sampling clock.
), a color subcarrier regeneration circuit (53) that extracts a color burst signal from the composite color television signal digitized by the A/D conversion circuit and regenerates a digital color subcarrier synchronized therewith; a separation circuit (54) for separating a luminance signal and a carrier color difference signal from the composite color television signal digitized by the D conversion circuit (52); and a separation circuit (54) for reproducing the carrier color difference signal from the separation circuit (54) into the color subcarrier. A color difference signal demodulator comprising a synchronous detection circuit (55) that demodulates a color difference signal by performing synchronous detection using digital color subcarriers reproduced by the circuit.