Photosensor circuit capable of detecting minute light signal...

Details Photosensor circuit capable of detecting minute light signal... Photosensor circuit capable of detecting minute light signal...

2005-06-21

2005-06-21

Garber, Wendy R. (Department: 2612)

Television

Camera, system and detail

Solid-state image sensor

Reexamination Certificate

active

06909462

ABSTRACT:
A photosensor circuit comprises a photodiode PD, which converts a light signal into electricity, an n-channel MOS transistor QD1which has a logarithmic characteristic in its weakly reversed condition and converts a sensor current generated by the photodiode PD into a detection voltage which has a logarithmic characteristic, and a capacitor which is connected to a detection terminal of this transistor QD1. A resetting voltage VG=VS is applied to the gate G of the transistor QD1to lower the impedance between the drain and the source of the transistor for resetting the transistor to an initial condition. As the n-channel MOS transistor QD1is a depletion type n-channel MOS transistor, when this transistor QD1does not receive any gate voltage, the transistor stays in a weakly reversed condition and has a logarithmic characteristic. This photosensor circuit has a high SN ratio and is capable of detecting minute light signals in high precision. Furthermore, it shows no after-image phenomenon and requires a relatively small number of power sources.

REFERENCES:
patent: 5539461 (1996-07-01), Andoh et al.
patent: 5650643 (1997-07-01), Konuma
patent: 5861621 (1999-01-01), Takebe et al.
patent: 5880460 (1999-03-01), Merrill
patent: 5903021 (1999-05-01), Lee et al.
patent: 6184055 (2001-02-01), Yang et al.
patent: 6242728 (2001-06-01), Merrill et al.

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