Pixel structure for imaging devices

• US 20030020001A1
• Filed: 06/28/2002
• Published: 01/30/2003
• Est. Priority Date: 02/10/1997
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Dierickx, Bart
• Granted Patent: US 6,917,029 B2
• Time in Patent Office: Days
• US Class Current: 250/208.1
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H04N 25/573 the logarithmic type
• CPC Class Codes: H04N 25/62 Detection or reduction of noise due to excess charges produced by the exposure, e.g. smear, blooming, ghost image, crosstalk or leakage between pixels
• CPC Class Codes: H04N 25/67 applied to fixed-pattern noise, e.g. non-uniformity of response
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/673 by using reference sources
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• CPC Class Codes: H04N 25/771 comprising storage means other than floating diffusion
• CPC Class Codes: H04N 3/1568 for disturbance correction or prevention within the image-sensor, e.g. biasing, blooming, smearing correction circuits H04N25/62

Abstract

Pixel structures and a read-out method of pixels are disclosed. The pixel structures and the read-out method improve the image quality of imaging devices or imaging sensors based on such pixels. A pixel comprises in a parallel circuit configuration a radiation sensitive element and an adjustable current source, said current source being adapted for delivering a high current. A 4-transistor pixel structure is also disclosed. A method of obtaining a calibrated read-out signal of a pixel having at least a photosensitive element and a current source comprise a number of steps. A photocurrent generated on the pixel added to a current generated by a current source in parallel with the photosensitive element is read to obtain a first signal. The pixel is also read with the current source off to obtain a second signal. The first signal is subtracted from the second signal, and the resulting signal is amplified to obtain the read-out signal.

Claims

1. A pixel for imaging applications fabricated in a MOS technology, said pixel comprising:

photosensitive element and a first transistor having a gate and a first and second electrode and being in series with said photosensitive element, said first transistor and said photosensitive element thereby forming a first connection;

a second transistor having a gate, said second transistor being coupled to said first connection, thereby forming a second connection, and said second transistor being part of an amplifying circuit; and

a third transistor having a gate and having two electrodes, said third transistor being connected in said second connection between said first connection and said second transistor;

whereby the gate of the first transistor and the gate of the third transistor are electrically coupled together to a same DC voltage.

2. The pixel as recited in claim 13, wherein said gate of said first transistor is at a first voltage and said first electrode of said first transistor is at a second voltage, said second electrode of said first transistor being connected to said photosensitive element, said gate of said second transistor being connected to said third transistor.

3. The pixel as recited in claim 14, wherein said gate of said first transistor is at said first voltage and wherein one of said electrodes of said third transistor is connected to said gate of said second transistor and the other of said electrodes is connected to said first connection.

4. The pixel as recited in claim 13, wherein said gate of said first transistor is at a first voltage and said first electrode of said first transistor is at a second voltage, said second electrode of said first transistor being connected to said photosensitive element.