JPH0210989A - Color difference signal demodulation circuit - Google Patents

Abstract

PURPOSE:To realize a demodulation circuit with fewer hardwares than a conventional method by using a complex number coefficient filter so as to process an input carrier color difference signal into a complex number signal and multiplying it with a complex number sinusoidal wave signal of a chrominance subcarrier frequency in a color difference signal demodulation circuit for a color TV receiver. CONSTITUTION:A reception signal of a color receiver is subjected to video detection, subjected to YC separation and a carrier color difference signal C is fed to an input terminal. A complex number filter 1 extracts a signal of 2.1MHz-4.2MHz and applies complex number signal processing and the result is subjected to frequency shift by complex number sinusoidal wave multipliers 3, 4. A color signal I1 obtained from the multiplier 3 is subjected to residual side band modulation and a signal I2 is subtracted from the said color signal to demodulate a broad band I signal having a flat spectrum. Thus, no harmonic wave is generated and a filter to eliminate it is not required.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the demodulation of quadrature-phase modulated waves, and particularly to a color difference signal demodulation circuit suitable for demodulating color difference signals in a color television (TV) receiver.

[Conventional technology]

Color difference signals in color TVs are transmitted using quadrature phase modulation. Conventionally known methods for demodulating orthogonal phase modulated waves include a method of multiplying by an orthogonal carrier wave and extracting the modulated signal with a low-pass filter, and a method of using a Hilbert converter. An example of modulating and demodulating a color difference signal using the latter method is disclosed in Japanese Patent Laid-Open No. 62-298295.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, in the method of multiplying orthogonal carrier waves, the sum and difference components of frequencies are output, and a filter is required to remove either unnecessary signal component. In addition, the method using a Hilbert transformer does not generate unnecessary components and does not require a filter, but the hardware required to implement the Hilbert transformer for converting a real signal into a complex signal is large-scale and complicated. , compared to the conventional method using real signals,
Both methods had the disadvantage of requiring more hardware.

An object of the present invention is to provide a device for demodulating orthogonally modulated signals such as color signals using a multi-coefficient filter, and further to realize a demodulation circuit with less hardware than conventional methods. There is a particular thing.

Means for Solving CAM] The above purpose is to construct a complex coefficient filter by using a complex coefficient filter to complexize the real signal and further selecting the sampling frequency to be four times the color subcarrier frequency fsc. And by simplifying the configuration of the multi-line sine wave signal multiplier,
achieved.

A complex coefficient filter can be designed by frequency shifting the frequency characteristics of a real coefficient filter. The transfer function of the FIR filter with N-th real coefficients is H(z)=ao
+azz-'+azz-''+-+a N Z-N.Z=ejcvT.Here, if the frequency characteristic is shifted by fα, 2 becomes jhc(f-/a)T −j2πfaT=
z(z, -1a)z=s
=ze. Substituting this into H(z):

H(z')=ao+a+α-"z-'+aza-"z
-"+-・+aNcx"'r4z" = (2),
In other words, a filter whose coefficients are complex numbers is obtained.

When a real signal is input to this filter, a complex signal is obtained,
Orthogonal demodulation is performed by multiplying this by a compound sine wave signal.

The input quadrature modulated wave is a cosωot + bsinωO
Let it be t.

The signal obtained by converting this into a compound signal is x (t) = acosωot+bsinωot+j(
asinωat-bcosωot). Add to this the complex sine wave −jcvo″=cosωot −jsinωo
When multiplied by t, the output y(t) is y(t)=x(t)・e
−”0t=a+j b −(3), and the real part is a
, b is output to the imaginary part and demodulated. Furthermore, unlike in real signal processing, there is no generation of harmonics (
2O2 component), so a filter to remove this is not necessary.

[Effect]

In the above explanation, the frequency shift amount of the complex coefficient filter and the frequency of the complex sine wave were arbitrary. Here, if the sampling frequency is chosen to be four times the color subcarrier frequency (f sc ) and the amount of one frequency shift is f sc , the coefficients of the complex coefficient filter and complex sine wave multiplication become simple. (1
), if T=4fsc=Jα=fsc.

Then, H(z') = ao -a2z-2+ atz
Ichibanichi・)+j(alz-1aaz-'+asz-'-
-), and the coefficients are real numbers or pure imaginary numbers.

The number of coefficients is the same as the number of original real coefficient filters,
Therefore, it can be realized with the hardware equivalent to one low-pass filter in actual signal processing, and the number of filters can be reduced.

(Two filters are required in real signal processing.) Next, for complex sine wave multiplication, equation (3) is performed by hardware, but it is determined whether ωo=2πfsc, T= or fsc ”1+ J+ 1−+ j+1 . . . In other words, if the sampling frequency is selected to be 4 fsc, multiplication of the multi-line sine wave can be performed only by code conversion and exchanging the real and imaginary parts, and no multiplier is required.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, 1 and 2 are complex coefficient filters, 3 and 4 are complex sine wave multipliers, 5 is an adder/subtractor, and 6 and 7 are coefficient multipliers. A TV signal received by a color receiver is image-detected and separated into Y and C signals, and a carrier color difference signal C is applied to the input terminal of FIG. Here, complex coefficient filters 1 and 2 convert them into complex signals, and complex sine wave multipliers 3 and 4 multiply them by a complex sine wave cosωsct+1sinωsct to shift the frequency of the signals, resulting in Iz, 2Iz, 2Q
Output each. 2I2, 2Q are coefficient multipliers 6, 7
is multiplied by 1/2, and Iz is further subtracted from Iz by an adder/subtractor 5 to obtain an engineering signal. A signal spectrum diagram is shown in FIG. The carrier color signal is obtained by orthogonally modulating fsc with signals I and Q having different bands as shown in FIGS. 2-8. Complex filter 2 is 3, 1 MHz to 4
, 2 MHz signals are extracted and made into complex signals. Complex filter 1 is 2.1 MHz to 4.2
The MHz signal is extracted and complexized.

When the frequency is shifted by complex sine wave multipliers 3 and 4, the second -b
The signal shown in the figure is obtained. Since the color signal signal 1 obtained from the complex sine wave multiplier 3 is vestigial sideband modulated, 2-
The spectrum will be as shown in figure b. By subtracting step 2 from this, a broadband signal with a flat spectrum can be demodulated.

〔Effect of the invention〕

A conventional circuit having the same function as that shown in Fig. 1 is shown in Fig. 3.
In the figure, 31.32 is a frequency mixer, 33.degree. 34.35 is a low-pass filter for removing harmonic components, 36.37 is a coefficient multiplier, and 38 is an adder/subtractor.

As can be seen in Figure 3, two L
A PF is required, and the LPF 34 has exactly the same configuration as the LPF 35. In the embodiment of FIG. 1, the present invention has one less filter than the conventional example, and it can be seen that the configuration hardware can be reduced. Note that the filter 1 and multiplier 3 shown in FIG. 1 can also be constructed by replacing them with a conventional method.

According to the present invention, since demodulation is performed by complex signal processing, there is no generation of unnecessary components (generation of harmonics) unlike in real signal processing, and a filter for removing these components is not required. Also, unlike complex processing using a conventional Hilbert transformer, since a multi-coefficient filter is used, the hardware is extremely small and is no different from a real coefficient filter. Furthermore, by selecting the operation sampling frequency to be four times the color subcarrier frequency, complex sine wave multiplication can be realized using only switches and polarity switching, which has the effect of simplifying the configuration of the color difference signal demodulation circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a color difference signal demodulation circuit according to the present invention, FIG. 2 is a spectrum diagram illustrating the operation of the structure of FIG. 1, and FIG. 3 is a diagram of a conventional color difference signal demodulation circuit. 1.2... Multiple coefficient filter, 3, 4... Complex sine wave multiplier, 5, 38... Addition/subtraction device, 6, 7, 36°3
7... Coefficient multiplier, 31.32... Frequency mixer,
Part 1 Part 22

Claims (1)

[Claims] 1. Demodulating the carrier color difference signal in a color TV receiver,
In a color difference signal demodulation circuit that reproduces two color difference signals I and Q, the input carrier color difference signal is converted into a complex signal by a complex coefficient filter, and this is multiplied by a complex sine wave signal of the color subcarrier frequency to obtain the real part of the output complex signal. A color difference signal demodulation circuit characterized in that I and an imaginary part are Q. 2. The color difference signal demodulation circuit according to claim 1, wherein the sampling frequency is set to four times the color subcarrier frequency when sampling the input signal input to the complex coefficient filter. . 3. The color difference signal demodulation circuit according to claim 1, further comprising a circuit for demodulating only the second I signal from the input carrier color difference signal, and subtracting 1/2 of the I signal from the second I signal. A color difference signal demodulation circuit is characterized in that it demodulates a wideband I signal by obtaining a calculated signal.