|Publication number||USRE41144 E1|
|Application number||US 11/203,651|
|Publication date||Feb 23, 2010|
|Priority date||Feb 15, 1999|
|Also published as||US6618080|
|Publication number||11203651, 203651, US RE41144 E1, US RE41144E1, US-E1-RE41144, USRE41144 E1, USRE41144E1|
|Original Assignee||Watec Co., Ltd.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (24), Classifications (10), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
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
This invention relates to processing circuit d which is explained in more detail. As shown in
To obtain composite video signal S1, processing circuit d is constructed as shown in FIG. 7. Input signal S1 is amplified to a predetermined level V1 in AGC amplifier e and transduced into constant level signal S3. On the other hand, signal S4 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 S3, 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 S2 shown in FIG. 6. In the composite video output signal, S2, the S/N (signal to noise) ratio is set to more than 40 dB (1%). This invention concerns the S/N ratio.
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.
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).
The above and other objects, advantages and novel features of this invention will be more fully understood from the following detailed description and the accompanying drawings, in which like reference numbers indicate like or similar parts throughout wherein:
FIG. 2(A) shows the relation of object Lux (abscissa) and video output voltage (ordinate) of a prior device (dotted line) and this invention. (B) shows the relation of object Lux (abscissa) and S/N ratio (ordinate) of this invention. (C) shows the relation of object Lux (abscissa) and gain of auxiliary amplifying circuit m (ordinate) of this invention.
According to claim 1 of this invention, signal processing circuit d of a video camera using a CCD, area sensor etc. is increased in an auxiliary amplifying circuit m, the amplification degree of the auxiliary amplifying circuit m being raised according to necessity so as to maintain the video output voltage at a predetermined voltage and vary the amplification degree of the processing circuit d so that the range of photographing is broadened.
According to claim 2 of this invention, signal processing circuit d of a video camera using a CCD, area sensor etc. provides an automatic gain control auxiliary amplifying circuit m1 of high S/N ratio, low amplification degree and automatic gain control auxiliary amplifying circuit m2 of low S/N ratio, high amplification degree. According to necessity, it is possible to selectively use automatic gain control auxiliary amplifying circuit m1 of high S/N ratio or automatic gain control auxiliary amplifying circuit m2 of low S/N ratio.
According to claim 3 of this invention, signal processing circuit d of a video camera using a CCD, area sensor etc. the function of said two automatic gain control auxiliary amplifying circuits m1 and m2 in claim 2 are included in one AGC amplifying circuit em which functions are switched by outer switching.
According to claim 4 of this invention, to detect the change of object illumination, the output voltage or the signal level in signal amplifying process is detected.
As shown in
Operation of above device is as follows:
In normal photography, the amplification degree is 0 dB.
AGC level detector r monitors video output signal S2 and if the image signal is lower than 0.72 v, the output of level detector r changes and the amplification degree of the auxiliary amplifying circuit m increases.
By said feedback operation, the video output voltage is maintained at a regular voltage of 0.72 v.
In the first embodiment, auxiliary amplifying circuit m is newly inserted between low pass filter g and gamma correction circuit h, but may be inserted between gamma correction circuit h and white clip circuit i, or between AGC amplifier e and low pass filter g, or between signal input part 1 and AGC amplifier e.
The above relationships are shown in the graphs of FIGS. 2(A), (B), (C). FIG. 2(A) shows the relationship of object Lux (abscissa) and video output voltage (ordinate) of the prior device (dotted line) compared with this invention. The hatched lines shows the broadened range for photographs in this invention. FIG. 2(B) shows the relationship of object Lux (abscissa) and S/N ratio (ordinate) of this invention.
In this invention, as shown in FIG. 2(C), the object Lux is lower than 0.02 Lux, the amplification degree increases, and photographing is possible until an object of Lux 0.002 Lux. But the S/N ratio is lowered to 25 dB as shown in FIG. 2(B).
As shown in
As shown in FIG. 2(C), the object illumination is higher than 0.02 Lux, amplification degree automatic gain control auxiliary amplifying circuit m1 of high S/N and low amplification degree 0 dB to 26 dB works. For an object illumination lower than 0.02 Lux, high amplification degree automatic gain control auxiliary amplifying circuit m2 works, and the amplification degree increases. However the S/N ratio is lower than 25 dB as shown in FIG. 2(B).
As shown in
Maximum amplification degrees are 0 dB to 26 dB and 0 dB to 46 dB and their amplification degrees are selected by switch S. Level of entering light are detected by level detecting circuit r and controls the switch S and set the amplification degree to a suitable value.
As explained in the construction, the same effects are accomplished.
According to this invention, in the case of sufficiently bright object, photographing is performed by conventional circuit, in the case of insufficient bright object, inserting auxiliary amplifying circuit m, m1, m2 or em, ignoring the S/N ratio, and raising the amplification degree, in the case of a sufficient bright object, photographing is performed by high S/N ratio, and high degree, in the case of insufficient bright object, inserting auxiliary amplifying circuit m, m1, m2 or em, and ignoring S/N ratio, utility photographing is possible.
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|JPS63119388A||Title not available|
|U.S. Classification||348/229.1, 348/E05.041, 348/366, 348/364|
|International Classification||H04N5/243, H04N5/14, H04N5/235, H04N5/238|
|Dec 16, 2010||FPAY||Fee payment|
Year of fee payment: 8
|Nov 28, 2014||FPAY||Fee payment|
Year of fee payment: 12