Four-component pixel structure leading to improved image quality

• US 6,917,029 B2
• Filed: 06/28/2002
• Issued: 07/12/2005
• Est. Priority Date: 02/10/1997
• Status: Expired due to Term

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Dierickx, Bart
• Primary Examiner(s): Luu, Thanh X.
• Application Number:
  US10/187,479
• Publication Number:
  US 20030020001A1
• Time in Patent Office: 1,110 Days
• Field of Search: 250/208.1, 250/214.R, 250/214.1, 348/297, 348/302
• 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:

a photosensitive element and a first transistor having a gate and a first and second electrode, the first electrode of the first transistor and said photosensitive element being directly connected to a same node;

a second transistor having a gate, said second transistor being coupled to said node, thereby forming a 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 connection between said node and said second transistor, the gate of the first transistor and the gate of the third transistor being electrically coupled together to a same DC voltage;

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 node.

2. The pixel as recited in claim 1, 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.

3. The pixel as recited in claim 1, further comprising an adjustable current source in a parallel configuration to the photosensitive element, the current source being adapted for delivering a high current.