Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
2000-01-25
2003-09-09
Vu, Ngoc-Yen (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C348S364000, C348S366000
Reexamination Certificate
active
06618080
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a signal amplifying circuit in a CCD (Charge Couple Device) camera using an area image sensor for use in a device such as a monitoring video camera.
2. Background Information
Heretofore, as shown in
FIG. 5
, in a conventional CCD camera, a light signal passed through lens a is transduced into signal S
1
, by CCD sensor b. The signal S
1
is a sampling held in CDS c as signal S
1
, the signal S
1
is processed in processing circuit d and output from signal input part
1
as signal S
2
as shown in FIG.
6
.
This invention relates to processing circuit d which is explained in more detail. As shown in
FIG. 5
, OSC (oscillator)
2
generates a synchronizing signal, timing generator
3
drives a CCD, V driver
4
is an iris signal S
4
output from processing circuit d for an automatic iris.
To obtain composite video signal S
1
, processing circuit d is constructed as shown in FIG.
7
. Input signal S
1
is amplified to a predetermined level V
1
in AGC amplifier e and transduced into constant level signal S
3
. On the other hand, signal S
4
amplified in fixed amplifier f is output as a control signal of a lens having an automatic iris or control signal for inputting a light limiting circuit. Operation of above device is as follows:
Signal S
3
, AGC, amplified in AGC amplifier e is passed by low pass filter g, to remove a useless wide frequency component, passed through gamma correction circuit h, white clip circuit i, composite sync mixer j, driver k (matching to 75 ohm line) and output as a video output signal S
2
shown in FIG.
6
. In the composite video output signal, S
2
, the S/N (signal to noise) ratio is set to more than 40 dB (1%). This invention concerns the S/N ratio.
Problems to be Solved by This Invention.
If an object is illuminated by a sufficient light source of more than 0.02 lux, the S/N ratio is kept more than 40 dB (1%) and no problems occur, but in low illumination such as night, photographing is impossible. However, in night photographing, it is desired to broaden the range of illuminating until 0.02 lux under a wrong S/N ratio.
BRIEF DESCRIPTION OF THE INVENTION
This invention intends to eliminate said drawbacks, and an object of this invention is to provide a signal amplifying circuit in a CCD (Charge Couple Device) camera in which under a sufficient object illuminating conditions (normally more than 0.02 lux), photographing normal circuit construction (FIGS.
5
and
7
), while under a low object illuminating condition, photographing while ignoring the S/N ratio, by inserting auxiliary amplifying circuit m or raising the amplification factor of AGC amplifier e.
Namely, in this invention when photographing at normal object illumination, the photograph is at a high S/N ratio and high grade, but when photographing at a low object illumination, the photograph is at high noise and ignoring the utility 20 db S/N.ratio (noise component 10%).
The detection means of said low object illumination is an output level of fixed amplifier f or lowering of the video output level (FIG.
2
).
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O'Reilly David
Vu Ngoc-Yen
Watec Co., Ltd.
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