Television – Image signal processing circuitry specific to television – Chrominance signal demodulator
Reexamination Certificate
2000-11-07
2003-05-20
Miller, John (Department: 2614)
Television
Image signal processing circuitry specific to television
Chrominance signal demodulator
C348S639000, C348S726000, C348S727000, C348S537000, C348S507000
Reexamination Certificate
active
06567129
ABSTRACT:
TECHNICAL FIELD
The present invention relates to color demodulation apparatuses and, more specifically, to an apparatus color-modulating a chrominance subcarrier signal separated from a composite television video signal through digital processing.
BACKGROUND ART
With recent advances in video quality, digitalization of television video signals has been required. To cope with digitalization, a color demodulation apparatus such as disclosed in Japanese Patent Laid-Open Publication No. 8-140114 (hereinafter referred to as prior document) has been suggested for color signal demodulation.
The conventional color demodulation apparatus disclosed in the above prior document is described below.
FIG. 11
shows a block diagram illustrating the configuration of the conventional color demodulation apparatus disclosed in the above prior document.
In
FIG. 11
, the conventional color demodulation apparatus includes a BPF circuit
101
, multiplier circuits
102
to
104
, first LPF circuits
105
and
106
, accumulator circuits
107
and
108
, second LPF circuits
109
and
110
, a VCO circuit
111
, a SIN data generator circuit
112
, and a comparator circuit
113
.
The BPF circuit
101
is a band-pass filter circuit allowing passage of the frequency band of a chrominance subcarrier signal. The BPF circuit
101
is supplied with the chrominance subcarrier signal separated from a composite digital video signal, and eliminates signal components of an unnecessary frequency band. According to gain control from the comparator circuit
113
which will be described later, the multiplier circuit
102
controls its output to keep a predetermined amplitude with respect to the received chrominance subcarrier signal. This control is generally called Auto Color Control (hereinafter referred to as ACC). The multiplier circuit
103
is supplied with the chrominance subcarrier signal after ACC processing outputted from the multiplier circuit
102
, and multiplies the chrominance subcarrier signal by a 90-degree-phase-shifted SIN wave signal outputted from the SIN data generator circuit
112
for R-Y demodulation. The multiplier circuit
104
is supplied with the chrominance subcarrier signal after ACC processing outputted from the multiplier circuit
102
, and multiplies the chrominance subcarrier signal by a 180-degree-phase-shifted SIN wave signal outputted from the SIN data generator circuit
112
for B-Y demodulation. The first LPF circuit
105
is a low-pass filter allowing passage of the frequency band of an R-Y signal, eliminating predetermined high frequency band components (such as noise) from a signal after demodulation by the multiplier circuit
103
and then outputting the R-Y signal. The first LPF circuit
106
is a low-pass filter allowing passage of the frequency band of a B-Y signal, eliminating predetermined high frequency band components (such as noise) of a signal after demodulation by the multiplier circuit
104
and then outputting the B-Y signal.
The R-Y signal from the first LPF circuit
105
is fed to the accumulator circuit
107
. The accumulator circuit
107
accumulates the R-Y signal during a burst signal period of one horizontal period, that is, a burst signal according to a burst gate pulse (hereinafter referred to as BGP) from a horizontal deflection apparatus (not shown). The accumulated the burst signal is supplied through the second LPF circuit
109
to the VCO circuit
111
. The VCO circuit
111
is a voltage controlled oscillator circuit capable of varying the period of a ramp wave, which is an output signal therefrom, according to the magnitude of a received signal. According to the received accumulated burst signal, the VCO circuit
111
controls the period of the ramp wave to be outputted to synchronize with that of the burst signal. Using the ramp wave from the VCO circuit
111
, the SIN data generator circuit
112
generates a 90-degree-phase-shifted SIN signal and a 180-degree-phase-shifted SIN signal with respect to the period of the ramp wave, and then outputs the 90-degree-phase-shifted SIN signal to the multiplier circuit
103
and the 180-degree-phase-shifted SIN signal to the multiplier circuit
104
.
By constituting a feedback loop as described above (hereinafter referred to as first feedback loop), the conventional color demodulation apparatus can perform accurate R-Y and B-Y demodulation always in synchronization with the burst signal.
On the other hand, the B-Y signal from the first LPF circuit
106
is fed to the accumulator circuit
108
. Like the above, the accumulator circuit
108
accumulates a burst signal according to a BGP from the horizontal deflection apparatus. The accumulated the burst signal is supplied through the second LPF circuit
110
to the comparator circuit
113
. The comparator circuit
113
has a predetermined reference value therein, and compares the value of the accumulated burst signal from the second LPF circuit
110
with the reference value. The comparator circuit
113
then controls gain of the multiplier circuit
102
so that the value of the accumulated burst signal matches the reference value.
By constituting a feedback loop as described above (hereinafter referred to as second feedback loop), the conventional color demodulation apparatus can always obtain a constant color signal amplitude.
In the conventional color modulation apparatus, however, the circuit for R-Y demodulation (the multiplier circuit
103
and the first LPF circuit
105
) and the circuit for B-Y demodulation (the multiplier circuit
104
and the first LPF circuit
106
) are formed individually. Furthermore, part of the circuits constituting the first feedback loop (the accumulator circuit
107
and the second LPF circuit
109
) and part of the circuits constituting the second feedback loop (the accumulator circuit
108
and the second LPF circuit
110
) are provided individually.
Therefore, the above conventional color demodulation apparatus has plural multiplier circuits, accumulator circuits, and LPF circuits, all or part thereof performing similar operation, thereby making the apparatus large in size.
Therefore, an object of the present invention is to provide a color demodulation apparatus having color demodulation capabilities as the conventional ones, with its size reduced by sharing part of processing circuits therein.
DISCLOSURE OF THE INVENTION
The present invention has the following features to solve the problem above.
A first aspect of the present invention is directed to a color demodulation apparatus color-demodulating a chrominance subcarrier signal separated from a composite television video signal through digital processing, comprising:
a frequency divider circuit for generating a predetermined load clock (hereinafter referred to as RCLK) using a system clock (hereinafter referred to as SCLK) which is an operational reference for the apparatus;
a band-pass filter circuit, supplied with the chrominance subcarrier signal, for eliminating signal components of an unnecessary frequency band from the chrominance subcarrier signal;
a first multiplier circuit, supplied with the chrominance subcarrier signal from the band-pass filter circuit, for controlling the chrominance subcarrier signal to be outputted therefrom to keep constant amplitude according to gain controlled by a comparator circuit;
a second multiplier circuit, supplied with the chrominance subcarrier signal after amplitude control outputted from the first multiplier circuit and a phase alternate SIN wave signal outputted from a SIN data generator circuit, for multiplying the signals together for multiplex demodulation of an R-Y signal and a B-Y signal;
a first low-pass filter circuit, supplied with a multiplex-demodulated signal from the second multiplier circuit, for passing frequency bands of the R-Y signal and the B-Y signal and eliminating predetermined high frequency band components;
a first load hold circuit, supplied with the multiplex-demodulated signal with the high frequency band components eliminated outputted from the first low-pass filter circuit, for separating the mul
Ando Hiroshi
Moribe Hiroshi
Morita Hisao
Shibutani Ryuichi
Taketani Nobuo
Desir Jean W.
Matsushita Electric - Industrial Co., Ltd.
Miller John
Wenderoth , Lind & Ponack, L.L.P.
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