Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-08-27
2001-10-09
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S208100
Reexamination Certificate
active
06300615
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus for performing logarithmic compression of light signal quantity into logarithmic output, and a photoelectric conversion apparatus making use of a phototransistor.
2. Related Background Art
There are conventional photoelectric conversion apparatus including those for providing a linear output signal against signal current quantity and those for providing a logarithmically compressed output signal in order to gain a wide dynamic range. A prior art example of such logarithmic compression type photoelectric conversion apparatus is one making use of a so-called logarithmic amplifier.
FIG. 1
shows an example of circuitry of the logarithmic amplifier. In
FIG. 1
, numeral
1
designates a photodiode,
2
an operational amplifier (op amp),
3
a diode,
4
a constant-potential input, and
5
an output terminal. When light is incident to the photodiode
1
, a photocurrent according thereto flows into the negative input terminal of op amp
2
. In the so-called logarithmic amplifier composed of the operational amplifier (op amp)
2
, the diode
3
, the constant-potential input
4
, and the output terminal
5
, the diode
3
is interposed between the output terminal
5
and the negative input side of an inverting input terminal. In such a coordinate system that light quantity/photocurrent is represented on the axis of abscissa while output potential at the output terminal is on the axis of ordinate, a light quantity produces a logarithmically compressed output with flow of a photocurrent to the diode
3
. The wide dynamic range property can be achieved in this way.
In the above prior art example, however, one op amp has to be assigned to one light signal current. Therefore, the prior art example had such a drawback that when the prior art example was applied to the photoelectric conversion apparatus composed of an array of many photodiodes, the apparatus needed to have op amps in the same number as the number of pixels and this increased the area and the supply current of the apparatus.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a photoelectric conversion apparatus that permits the logarithmic compression of light signal in a simple circuit configuration.
Another object of the present invention is to provide a photoelectric conversion apparatus using a phototransistor with good optical response.
In order to accomplish the above object, according to one aspect of the present invention, there is provided a photoelectric conversion apparatus comprising a pair of transistors whose respective control electrodes are connected to each other, and a capacitor, wherein said pair of transistors are arranged so that a potential of a main electrode of one transistor is fixed to a constant potential and so that a main electrode of the other transistor is connected to said capacitor, and wherein a voltage or a charge appearing in said capacitor is taken out as a signal.
According to another aspect of the invention, there is provided a photoelectric conversion apparatus comprising a phototransistor having a control electrode portion for receiving light and a main electrode portion for outputting a signal, and potential control means for changing a potential of the main electrode portion without variation of a potential of the control electrode portion.
Other features and objects of the present invention will become more apparent by the description of the specification which follows.
REFERENCES:
patent: Re. 34309 (1993-07-01), Tanaka et al.
patent: 5288988 (1994-02-01), Hashimoto et al.
patent: 5424529 (1995-06-01), Hashimoto et al.
patent: 5587738 (1996-12-01), Shinohara
patent: 5698844 (1997-12-01), Shinohara et al.
patent: 5737095 (1998-04-01), Kikuchi et al.
patent: 5991467 (1999-11-01), Kamiko
Kikuchi Shin
Shinohara Mahito
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Le Que T.
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