JPS60160287A - Digital color demodulator - Google Patents

Abstract

PURPOSE:To reduce the number of digital low-pass filters to be used by supplying a demodulated output to a digital low-pass filter and providing an adder at the posterior stage of an invertor or a output stage of the digital low-pass filter in a color television receiver. CONSTITUTION:A phase invertor 43 is constituted of an invertor 41 for inverting codes and an adder 42 as shown in the figure. LSB data, whose invertor output CD' and a logical level are ''1'', are supplied to the adder 42, and a digital carrier chrominance signal DD'' whose phase is digitally inverted is formed. In case of digital data, their phase inversion output cannot be constituted only by inverting their codes. This can be achieved by adding an LSB bit having a logical level ''1'' as shown in the figure to phase inversion data. A digital carrier chrominance signal CD and a phase-inverted digital carrier chrominance signal CD'' are multiplexed in a multiplexer 44.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a digital color television receiver in which a signal processing system for forming a television signal, a luminance signal, and a pair of component color signals is digitally configured. This invention relates to a digital color demodulator suitable for application to.

BACKGROUND ART AND PROBLEMS A digital color television receiver has been proposed in which a signal processing system is digitally configured to form a luminance signal and a pair of component color signals, for example, a pair of color difference signals, from a television signal.

FIG. 1 is a system diagram showing an example of this system, in which a television signal supplied to a terminal (1) is supplied to a zero converter (4) via a tuner (2) and a video intermediate frequency amplifier (3). The television signal is converted into a digital signal while remaining in the composite state. The digitized television signal is supplied to a Y/C separator (5), which separates it into a digital luminance signal YD and a digital carrier color signal CD, and the digital carrier color signal CD is sent to an ACC circuit (6). A pair of digital color difference signals (R-Y)D and (B-Y)D are demodulated.

These and the digital luminance signal YD are sent to the D/A & converter (
9) and is analog-converted into a luminance signal Y and a pair of color difference signals R-Y and B-Y.

These are supplied to the matrix circuit α and the primary color signal R
, G, and B are formed. These primary color signals R, G, and B are supplied to a cathode ray tube (not shown) to reproduce a predetermined color image.

In this example, the sampling frequency for φ-converting the television signal is 4f, where the carrier frequency is kfmc.
It has been selected by ac. Therefore, the digital carrier color signal CD
is output as a signal having a time series as shown in FIG. 3A. That is, a pair of digital color difference signals (B
-Y)D, (R-Y) are output as a digital signal having a time series such that they are obtained alternately in each sampling period. Here, a pair of digital color difference signals (B-Y
)D and (RY)D are obtained with their phases inverted every twice the sampling period.

A pair of digital color difference signals (B Y)n, (B Y)n't are obtained from the digital carrier color signal CD having such a time series.
- For demodulation, a digital color demodulator (e) as shown in FIG. 2 is used. FIG. 2 shows an example of this digital color demodulator (2), in which (20A) is a demodulation system that fully demodulates the blue color difference signal (n-Y)n;
B) is a demodulation system that demodulates the red color difference signal (RY)D. Digital carrier color signal CD supplied to terminal (13)
is the first D-type flip-flop CD with latch function.
and latches the -blue digital color difference number 4 (B-Y)D among those constituting the digital carrier color signal Cnk. The clock CK1 supplied to the first flip-flop (2]) has a frequency flI as shown in FIG. 3B.
C is a pulse with a duty of 50, and from this a digital color difference signal (B Y)o as shown in FIG. 3C is obtained.

Similarly, the digital carrier color signal CD is supplied to a second D-type fritz clock (221) which also has a latch function. For this reason, the second flip-flop (24) latches the phase-inverted digital color difference signal (B-Y) D of the time series in FIG. 3A. This latch output is supplied to a digital phase inversion circuit (to) to invert the phase of the digital data.The result is shown in FIG. 3E.

The phase-inverted digital color difference signal (B-Y) D2 and the above-mentioned digital color difference signal (B-Y) DI are added to the adder C241.
After being added to form a digital demodulated output, it is supplied to a digital loaf 4 filter (251) to form a digital color difference signal (B-Y)D having a predetermined frequency band.

A demodulation system (
20B) is similarly configured. Punishment and (c) are the third and fourth D-type flip-flops that have a latch function, and the clock CK2 supplied to the third flip-flop is out of phase with the clock CK1. is used. The clock CKQ supplied to the fourth fritz f(2) has the phase of the clock CK2'i inverted.

Clocks CK2, CK2 having such a phase difference
Of the digital carrier color signal CD shown in FIG. After that, the water is supplied to a digital low-pass filter and demodulated into a digital color difference signal (R-Y) D having a predetermined frequency band as described above.

By the way, when a digital color demodulator is configured in this way, it is necessary to provide a digital low-pass filter (2!19.oa'i) in the digital signal demodulation system, which increases the number of parts and reduces the circuit size. is causing an increase.

Purpose of the Invention The present invention takes all of these points into account and reduces the number of digital low-pass filters used, thereby reducing the circuit scale.

SUMMARY OF THE INVENTION Therefore, in the present invention, a pair of digital carrier color signals are obtained by sequentially and alternately obtaining a pair of component color signals in each sampling period, and a pair of digital carrier color signals are obtained through an inverter for inverting all signs of the digital carrier color signals. An adder is provided that supplies the signal to the multiplexer and its demodulated output to the digital low-pass filter, and adds LSB data of logic level "'1#" to the downstream stage of the inverter or the output stage of the digital low-pass filter. ,
The digital carrier color signal is demodulated into a digital color signal having a predetermined band.

Embodiment Next, an example of the digital color demodulator according to the present invention will be described in detail with reference to FIG. 4 and subsequent figures, regarding the case where it is applied to a television receiver that receives an NTSC television signal.

In FIG. 4, the ring indicates a digital demodulator, which is composed of a digital phase inverter (2) and a multiplexer (2), and a digital carrier color signal cn (A in FIG. 5) supplied to a terminal (40a). is supplied to the multiplexer 04, and a phase-inverted digital carrier color signal CD is also supplied.

As shown in the figure, the phase inverter (A) is composed of an inverter α for sign inversion and an adder), and the inverter output Cp
’ and the LSB data whose logic level is @1” are sent to the adder (
6) to form a digitally phase-inverted digital carrier color signal CD (FIG. 5B).

In the case of digital data, its phase-inverted output cannot be constructed simply by inverting its sign. This can only be achieved by adding the LSB bit of logic level "1" to the phase-inverted data as shown in the figure.

The digital carrier color signal Cn and the phase-inverted digital carrier color signal G are multiplexed in multiplexer 2. Clock CKa supplied to multiplexer■
As shown in FIG. Both digital carrier color signals C whose phases are inverted during the low level period Y.
D is imported.

As a result, the multiplex output CM is output with its polarity aligned as shown in the fifth diagram.

The multiplex output CM is supplied to a digital low-pass filter (digital low-pass filter) and given a predetermined frequency characteristic. In this example, a low-pass characteristic is provided such that the cutoff frequency is approximately I MHz.

(for the digital low-noise filter) as shown in the figure.

It is composed of a delay element (C) selected for the total delay time and an adder U. The output of the digital low-pass filter (2) is supplied to a switching circuit (2) having a latch function, and the digital color difference signals (RY)D and (B-Y)n are synchronized.

Therefore, the blue digital color difference signal (BY)D is latched during the high level period of the switching pulse CKI) supplied to the switching circuit (b) (FIG. 5F).
At the same time, during the low level period, the red color difference signal (R-Y)
D is latched (FIG. 5G) and synchronized.

FIG. 6 shows another example of the digital color demodulator according to the present invention. This is a case in which the adder α power provided in the low-noise filter (A) is also used. Therefore, the digital demodulation section (6) is provided with only the inverter 0 for sign inversion, whereas the digital low iJ? LSB data with a logic level of 1'' is further added to the adder 071 of the filter.

Even with this configuration, it is possible to digitally completely invert the phase of the predetermined digital data that constitutes the multiplex output, that is, the digital demodulation output CMk output from the adder α of the digital low-pass filter (A). become.

By the way, although the above-mentioned embodiment is a case in which the digital color demodulator (a) i according to the present invention is applied to an NTSC system color television receiver, it can also be applied to a PAL system digital color television receiver. can.

However, in this case, as shown in FIGS. 7A and 7B, the polarity of the data of the digital carrier color signal CD is inverted for each line, so the clock CKa supplied to the multiplexer
It is necessary to use different phases for each horizontal line.

That is, in the case of a digital carrier color signal CD having a polarity as shown in FIG.
In the +1 line, the digital carrier color signal CD is the seventh
Since the polarity as shown in FIG. B is obtained, at this time, a clock CKa2e whose phase is different from the clock CK, 1 by 1 is used as shown in the same figure.

In this way, the clock CKa1. which differs from line to line. C.K.
2, it is possible to demodulate the PAL digital carrier color signal CDk using the same circuit as shown in FIG. 4 or FIG. , (BY)D can be formed.

As described in detail, in this invention, the sign inversion demodulation method is adopted in the digital demodulation section (to). Since one digital low-pass filter to be provided can be omitted, the circuit scale can be reduced, and cost reductions can be easily achieved.

In addition, in the present invention, the low-pass filter for digital demodulation can also be used as a band-limiting filter, so the number of circuit elements can be further reduced. Further, in the present invention, by appropriately selecting the phase of the clock CKa supplied to the digital demodulator O0, the digital color demodulator 0! I vf-NT
It is versatile because it can be applied not only to SC type television receivers but also to PAL type television receivers.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a digital color television receiver to explain the present invention, FIG. 2 is a system diagram showing an example of a conventional digital color demodulator, and FIG. 3 is a diagram to explain its operation. , FIG. 4 and FIG. 6 are system diagrams showing an example of a digital color demodulator according to the present invention, and FIG.
7 and 7 are diagrams for explaining the operation, respectively. (4) is an A/D converter, (9) is a D/A converter, (5)
1 is a Y/C separator, 1 is a digital color demodulator, αQ is a digital demodulator, 2) is a digital low-pass filter, a ring is a phase inverter, and 2 is a multiplexer. ...Kゝ・ Agent Sadao Ito;

Claims (1)

[Claims] A digital carrier color signal in which a pair of component color signals are obtained alternately in each sampling period, and a digital carrier color signal obtained through an inverter for sign inversion are supplied to a multiplexer, and the demodulated output is filtered through a digital low-pass filter. At the same time, an adder is provided which adds LSB data of logic level "1" to the downstream stage of the inverter or the output stage of the digital signal filter, and the digital carrier color signal has a predetermined band. Digital color demodulator that demodulates to digital color ◎