Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-04-26
2001-10-16
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C257S291000, C348S307000
Reexamination Certificate
active
06303919
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a linear image sensor suitable for a facsimile or an image scanner which reads out image information and transmits it.
In a conventional linear image sensor, a light receiving element of a linear image sensor as disclosed in Japanese Patent Application Laid-open No. Sho 61-124171 is known.
FIG. 8
shows its structure. In
FIG. 8
, reference numeral
4
denotes a separation layer,
3
denotes an epitaxial layer and is a collector,
6
denotes a base, and
9
denotes an emitter.
SUMMARY OF THE INVENTION
However, since a base/collector junction portion is wide, junction capacitance is also large, and further, since a base region is in a floating state, there is a problem of persistence of vision that even if read images are changed from a bright state to a dark state, a signal of the previous bright state remains in the read signal, and there has been a problem that a clear image can not be obtained.
In order to solve the foregoing problem, in the present invention, a part of a light receiving element is made a light receiving MOS diode covered with an electrode permitting transmission of part of light, and when photo charges are stored, the light receiving MOS diode is operated in an inversion state, and generated photo charges are stored in its inversion region and a base region of a phototransistor, and at the time of resetting after reading to the outside, the light receiving MOS diode is made a storage state so that residual charges which were not able to be read to the outside are transferred to the base region, and in the state where the photo charge density of the base region is raised, resetting is made through an emitter so that the residual charges which become persistence of vision are reduced. At the time of reading as well, the light receiving MOS diode is made the storage state, so that photo charges stored under the light receiving MOS diode are transferred to the base region and the voltage between the base and emitter is made large, as a result of which, the bipolar transistor operation of the phototransistor is made easier, and improvement has been made to the characteristics contrary to the foregoing, that is, the rising characteristics that even when read images are changed from a dark state to a bright state, a read signal is slightly lower than a signal in a sufficiently bright state.
Moreover, to prevent an electric field of 0.7 MV/cm or more from being applied to a gate oxide film of the light receiving MOS diode, a base potential is limited, so that the influence of surface recombination current applied by an interface of the gate oxide film is stabilized, and further, improvement has been made to the leak of photo charges, which were not able to be absorbed, into the vicinity of an adjacent pixel in the case where light with high illumination is incident on a pixel under sunlight or fluorescent light. Moreover, at a waiting state, the potential of a gate of the light receiving MOS diode is fixed to a high voltage or made floating, so that improvement has been made such that an electric field is prevented from being applied to the gate oxide film of the light receiving MOS diode.
REFERENCES:
patent: 4562474 (1985-12-01), Nishizawa
patent: 4631592 (1986-12-01), Nishizawa
patent: 4673985 (1987-06-01), Nishuzawa
patent: 5844234 (1998-12-01), Kawazoe
Kawahara Yukito
Machida Satoshi
Shimizu Tooru
Yokomichi Masahiro
Adams & Wilks
Lee John R.
Seiko Instruments Inc.
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