Television – Image signal processing circuitry specific to television – A/d converters
Reexamination Certificate
1998-08-04
2002-06-04
Hsia, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
A/d converters
C348S689000, C348S712000, C348S713000
Reexamination Certificate
active
06400412
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video signal processing apparatus for converting an analog video signal composed of an analog luminance component signal and an analog chrominance component signal into a digital video signal and processing the digital video signal and for converting the processed digital video signal into a digital video signal and outputting the digital video signal.
2. Description of Related Art
In recent years, digital video apparatuses for digitizing analog video signals to record the digital signals on tapes or disks and reproduce the digital signals therefrom have begun to popularly spread. More specifically, digital video cameras and digital video disks are known as typical digital video apparatuses.
These digital video apparatuses cope with not only recording/reproduction of digital video signals but also recording/reproduction of conventional analog video signals.
FIG. 1
is a block diagram showing the arrangement of a conventional video signal processing apparatus for converting an analog video signal into a digital video signal. Referring to
FIG. 1
, reference numeral
103
a
denotes a low-pass filter (LPF);
123
a
, a band-pass filter (BPF);
104
a
and
125
a
, clamping circuits; and
105
a
and
126
a
, A/D converters.
In the video signal processing apparatus shown in
FIG. 1
, input signals
101
a
and
121
a
are an analog luminance (Y) signal and an analog chrominance (C) signal, respectively. After the luminance signal
101
a
is gain-controlled by an amplifier
102
a
to have a predetermined signal level, the luminance signal
103
aa
is subjected to band limit by the low-pass filter
103
a.
This LPF
103
a
has an amplitude attenuation characteristic of about −12 dB at a frequency of ½ is on the basis of a sampling clock frequency fs of an A/D converter, and also has a group delay time YDLY (nS) in a passing band (see FIG.
3
).
A luminance signal
103
ba
subjected to the predetermined band limit by the LPF
103
a
is inputted to the clamping circuit
104
a
. Then, a signal potential of the luminance signal
103
ba
is set by the clamping circuit
104
a
to be appropriate to the input range of the A/D converter
105
a
of the next stage. More specifically, a clamping operation of the clamping circuit
104
a
is performed such that, even if the average luminance level (APL) of a video signal varies, a pedestal level (black level) of the video signal serving as a reference becomes a fixed DC potential.
The A/D converter
105
a
converts an analog luminance signal
108
a
outputted from the clamping circuit
104
a
into a digital luminance signal
106
a
at a resolution of, e.g., 8 bits.
Similarly, after the chrominance signal
121
a
is a gain-controlled by an amplifier
122
a
to have a predetermined signal level the chrominance signal
123
aa
is subjected to band limit by the band-pass filter (BPF)
123
a.
A chrominance signal in the NTSC system has fsc=3.58 MHz, and a chrominance signal in the PAL system has fsc=4.43 MHz. The BPF
123
a
has a group delay time CDLY (nS) in a passing band (see FIG.
4
). A chrominance signal
123
ba
subjected to band limit by the BPF
123
a
is subjected to delay correction by a delay circuit
124
a
until the chrominance signal
123
ba
has the same timing as that of the luminance signal
103
ba.
Thereafter, a signal potential of a chrominance signal
130
a
outputted from the delay circuit
124
a
is set by the clamping circuit
125
a
to be appropriate to the input range of the A/D converter
126
a
. As in the luminance signal system, an analog chrominance signal
129
a
is converted into a digital chrominance signal
127
a
by the A/D converter
126
a.
Here, in a signal processing system for converting an analog video signal into a digital video signal, the characteristics of an analog filter for suppressing aliasing noise generated in sampling by the A/D converter
105
a
are important factors.
In the conventional signal processing system shown in
FIG. 1
, when the sampling frequency of the luminance signal
101
a
is set to be, e.g., 13.5 MHz, in order to keep the quality (frequency characteristic and pulse response characteristic) of a signal component in the passing band good, a group delay characteristic of about 300 to 800 nS is generally set by setting a cutoff frequency or the like.
Since the chrominance signal
121
a
has a narrow signal band, the BPF
123
a
is generally constituted by a BPF having the characteristics as shown in FIG.
4
. However, since the group delay time CDLY of the BPF
123
a
is shorter than the group delay time YDLY of the LPF
103
a
for a luminance signal, the delay circuit
124
a
must be provided to make the delay time of the chrominance signal
121
a
equal to the delay time of the luminance signal
101
a.
However, the presence of an analog delay circuit for adjusting signal delay, as in the conventional signal processing system, disadvantageously gives bad influence on suppressing the variations of delay timings of the luminance signal and the chrominance signal and assuring the precision of the delay timings, and degrades the quality of the signals, e.g., an S/N ratio or the like.
In addition, an input/output signal processing system for an analog signal in a digital video apparatus is advantageously constituted by a compact system at high precision and low cost by constituting peripheral circuits by ICs. However, from the viewpoints of the circuit scale and the power consumption, it is disadvantageous to constitute a delay circuit for correcting the timings of a luminance signal and a chrominance signal by an analog circuit.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a video signal processing apparatus capable of solving the above problems.
It is another object of the present invention to provide a video signal processing apparatus capable of reducing the variations of delay timings of a luminance component signal and a chrominance component signal and improving the precision of the delay timings.
To attain the above objects, in accordance with an aspect of the present invention, there is provided a video signal processing apparatus for converting an analog video signal composed of an analog luminance component signal and an analog chrominance component signal into a digital video signal and processing the digital video signal, which comprises (i) first analog/digital conversion means for inputting an analog luminance component signal and converting the inputted analog luminance component signal into a digital luminance component signal and for outputting the digital luminance component signal, (ii) second analog/digital conversion means for inputting an analog chrominance component signal and converting the inputted analog chrominance component signal into a digital chrominance component signal and for outputting the digital chrominance component signal, (iii) luminance component signal frequency band limiting means, disposed on a pre-stage of the first analog/digital conversion means, for limiting a frequency band of the analog luminance component signal to be inputted to the first analog/digital conversion means and for supplying the frequency-band-limited analog luminance component signal to the first analog/digital conversion means, (iv) chrominance component signal frequency band limiting means, disposed on a pre-stage of the second analog/digital conversion means, for limiting a frequency band of the analog chrominance component signal to be inputted to the second analog/digital conversion means and for supplying the frequency-band-limited analog chrominance component signal to the second analog/digital conversion means, the chrominance component signal frequency band limiting means having a group delay characteristic different from a group delay characteristic of the luminance component signal frequency band limiting means by a predetermined delay time, and (v) digital signal processing means for individually processing, a
Canon Kabushiki Kaisha
Hsia Sherrie
Robin Blecker & Daley
LandOfFree
Video signal processing apparatus with time adjustment of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Video signal processing apparatus with time adjustment of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Video signal processing apparatus with time adjustment of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2934081