Active pixel sensor using CMOS technology with reverse biased photodiodes
US5900623A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Aug 11, 1997 |
| Grant date | May 4, 1999 |
| Priority date | — |
| Expiry date | Aug 11, 2017 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N25/77
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
An active pixel sensor implemented with CMOS technology that employs a plurality of photocells, each including a photodiode to sense illumination and a separate storage node with a stored charge that is discharged during an integration period by the photocurrent generated by the photodiode. Each photocell includes a switching network that couples the photocurrent to the storage node only during the integration period while ensuring that a relatively constant voltage is maintained across the photodiode during integration and non-integration periods. The transistors in the switching network operate in a forward active subthreshold region, ensuring linear operation and the diode voltage is clamped to a small positive voltage so that the diode is always reverse-biased. A source-follower generates a output signal correlated to the charge on the storage node that is coupled to column output circuitry that samples the signal. An operational scheme is employed wherein the storage node is first set to a defined voltage, the photocurrent is allowed to discharge the storage node and then the remaining charge coupled as a first signal to the column output circuitry, which samples and stores th…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.