Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1999-02-02
2003-07-01
Christensen, Andrew (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C348S243000, C348S250000
Reexamination Certificate
active
06587144
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital camera, and more particularly, to an improved analog signal processing apparatus for a digital camera which is capable of carrying out a black level clamping with regard to a digital-converted image signal.
2. Description of the Background Art
In general, in a digital camera, the light from a lens is converted into an electrical signal via a charge coupled device (CCD). The converted electrical signal is sampled using a black level as a reference to generate a typical video signal which is then converted to a digital image signal via respective signal processing steps. Eventually, the converted digital image signal is outputted via a digital signal processor (DSP).
The digital signal converting process of carrying out the respective signal processing steps with regard to the analog signal will now be described with reference to the accompanying drawings.
As shown in
FIG. 1
, a conventional analog signal processing apparatus for a digital camera includes a correlated double sampling (CDS) circuit
10
adjusting a direct current (DC) level of an electrical signal from a CCD (not shown) by using a black level as a reference and converting the DC level electrical signal into a typical video signal, an automatic gain control (AGC) circuit
20
adjusting the gain of the output signal of the CDS circuit
10
and outputting a signal amplified by as much as a predetermined gain, an analog-to-digital (A/D) converter
30
converting the analog signal from the AGC circuit
20
into a digital signal and outputting the converted signal to a DSP (not shown), and a black level clamp circuit
40
comparing a black level signal from the AGC circuit
20
and a preset black level reference value V
REF
and carrying out a black level clamping.
The black level clamp circuit
40
includes a switch
41
connected to an output of the AGC circuit
20
and turned on/off under the control of a black level clamping signal BLKCLP outputted at time intervals from a clock generator (not shown), an analog comparator
42
comparing a signal corresponding to the black level from the AGC circuit
20
and the preset black level reference value V
REF
in accordance with the turning on of the switch
41
, and an integrator
43
determining an accurate black level required to the CDS circuit
10
in accordance with the compared result and applying the same to the CDS circuit
10
.
The analog signal processing steps for the conventional digital camera will now be explained.
The signal from the CCD is converted into a typical video signal via the CDS circuit
10
. At this time, the DC voltage of the video signal is adjusted with reference to a black level.
Here, the black level is adjusted at predetermined time intervals in accordance with the output of the black level clamp circuit
40
.
The video signal formed by the CDS circuit
10
is applied to the AGC circuit
20
and amplified therein depending upon a gain value, and then converted into a digital video signal in the A/D converter
30
.
Meanwhile, the switch
41
provided at the output terminal of the AGC circuit
20
is turned on/off in accordance with the black level clamping signal BLKCLP received at predetermined time intervals from the clock generator (not shown), and it transmits the output signal of the AGC circuit
20
to the analog comparator
42
.
As shown in
FIG. 2
, the black level clamping signal BLKCLP becomes active during non-image intervals B which occur between respective lines of a camera scan.
In the intervals B where the black level clamping signal BLKCLP becomes active, the switch
41
is turned on and accordingly a signal outputted from the AGC circuit
20
and corresponding to a black level is applied to the analog comparator
42
.
Then, the analog comparator
42
compares the present black level signal from the AGC circuit
20
and the preset black level reference value V
REF
. The integrator
43
levels up or down the black level value according to the compared result and feeds back the same to the CDS circuit
10
.
As a result, when the CDS circuit
10
converts the electrical signal which is received from the CCD into a video signal in accordance with the output signal of the integrator
43
to a video signal, the black level as its reference is accurately corrected and the DC voltage level of the video signal is adjusted, accordingly.
As described above, in the conventional digital camera, it is difficult to maintain the preset black level due to error factors such as a process error and an offset which occur in respective blocks inside the system, so that the black level clamping circuit
40
is provided which clamps the black level at predetermined time intervals for its solution.
However, the conventional black level clamp circuit
40
has difficulty in solving the offset voltage generated from the analog comparator
42
or the integrator
43
in the black level clamp circuit
40
, or the A/D converter
30
operating after the clamping performance. In order to solve the above drawbacks, an additional compensation block should be disadvantageously included in an initial circuit design.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming the conventional disadvantages.
Therefore, it is an object of the present invention to provide an analog signal processing apparatus for a digital camera, capable of carrying out a black level clamping with regard to a digital-converted image signal.
To achieve the above-described object, there is provided an analog signal processing apparatus for a digital camera according to the present invention which includes a correlated double sampling (CDS) circuit adjusting a direct current (DC) level signal from a charge coupled device (CCD) by using a black level as a reference and converting the DC level signal to a typical video signal, an automatic gain control (AGC) circuit automatically adjusting the gain of an output signal of the CDS circuit, an analog-to-digital (A/D) converter converting the analog signal from the AGC circuit into a digital signal, a black level clamp circuit clamping the black level of a digital image signal from the A/D converter for a predetermined time interval and feeding back the same to the CDS circuit, and a clock generator generating first and second clock signals and a black level clamping signal so as to control the timing of the black level clamp circuit.
The features and advantages of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific example, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 5121117 (1992-06-01), Rabii
patent: 5512947 (1996-04-01), Sawachi et al.
patent: 6005613 (1999-12-01), Endsley et al.
patent: 6157407 (2000-12-01), Kobayashi
patent: 07-162713 (1995-06-01), None
Birch & Stewart Kolasch & Birch, LLP
Christensen Andrew
Hynix / Semiconductor Inc.
Ye Lin
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