Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1996-10-31
2001-11-20
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Solid-state image sensor
C348S308000
Reexamination Certificate
active
06320617
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to the field of active pixel sensors, and more particularly to the architecture control circuits for active pixel sensors. More specifically, the invention relates to CMOS control circuits for active pixel sensors.
2. Description of the pior Art
Prior art active pixel sensors made from a CMOS process have used source/drain implants to form a photodiode, and polysilicon to form photogates as the light sensing elements. These light sensing elements have suffered from poor quantum efficiency, lag, and noise.
In order to overcome these problems, integration of a pinned photodiode in an active pixel sensor light sensing element was disclosed by Lee et al in U.S. Patent Application No. 08/421,173 to facilitate a pinned photo diode light sensing element within the architecture of an active pixel sensor. There is a shortcoming within this prior art device in that it does not show the manner in which the pixels are controlled by the control circuitry.
Prior art devices have numerous problems in integrating a camera system on a chip using CMOS process technology. These problems include column fixed pattern noise and the inability to fit the selection circuitry with the corresponding output amplifiers into a desired pixel pitch.
As can be seen by the foregoing discussion, there remains a need within the art for a method and apparatus of incorporating a pinned photodiode based image sensor within a CMOS device to alleviate fixed pattern noise, reduce the overall size of the device to achieve the desired pixel pitch, and to provide for a means to compensate for threshold voltage variation.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems set forth above. This invention relates to the circuit architecture of an x-y addressable image sensor, in particular to that of a Complementary Metal Oxide Semiconductor (CMOS) active pixel sensor (APS) array. The invention describes elements of circuits and their embodiments to operate an APS which has a Pinned Photo Diode as its image sensing element.
An active pixel sensor incorporating a pinned photo diode offers advantages over conventional photogate or photodiode based APS by having high quantum efficiency, low dark current, no image lag, and low reset noise. This invention summary describes the circuitry building blocks, architecture, and circuit elements used in building this sensor.
Briefly summarized, one aspect of the present invention, describes an active pixel sensor comprising: a substrate having an area divided into a plurality of pixel areas arranged in a series of row and columns, having at least one control area separate from the pixel areas; a pinned photodiode formed in at least one of the pixel areas of the substrate; a readout transistor integrated on the pixel area of the substrate and operatively coupled to the pinned photodiode through a transfer gate and a charge to voltage conversion means; at least one selection transistor integrated on the substrate that is capable of selecting one row of the pixel areas; a column selection circuit capable of selecting a group of pixels formed within the substrate in one of the control areas separate from the pixel areas, the selection circuit further comprising a column readout circuit including a double delta sampling circuit formed from a process that is compatible with CMOS technology; and a reset circuit. The present invention further comprises the use of overlapping gates to reduce the overall size requirements.
These and other aspects, objects, features, and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.
ADVANTAGEOUS EFFECT OF THE INVENTION
The present invention has the following advantages listed below:
Integrates the pinned photo diode light sensing element with specific control and readout circuitry to improve noise and spectral response characteristics;
Allows for integration of a camera system on a single chip using a CMOS process to provide reduced size and lower noise;
Provides a control and readout circuit having low noise with an active pixel sensor array having a pinned photodiode light sensing element; and
Improves the fixed pattern noise characteristics of a CMOS active pixel sensor.
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Fossum Eric R.
Gee Russell Clayton
Lee Paul Poo-Kam
Lee Teh-Hsuang
Eastman Kodak Company
Garber Wendy R.
Watkins Peyton C.
Wilson Jacqueline
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