Analog-to-digital conversion in image sensors
US8305474B2 · kind B2 · utility
Assignees
Inventors
Key dates
| Filing date | Nov 19, 2009 |
| Grant date | Nov 6, 2012 |
| Priority date | — |
| Expiry date | Jan 26, 2031 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N25/78
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
An image sensor has a per-column ADC arrangement including first and second capacitors allowing a comparator circuit to perform correlated double sampling. The capacitors are continuously connected to, respectively, the analog pixel signal and a ramp signal without use of a hold operation. The comparator circuit comprises a differential input being connected to the junction of the two capacitors and being biased by a reference signal. The reference signal is preferably sampled and held from a reference voltage. The use of a differential input as first stage of the comparator addresses problems arising from ground voltage bounce when a large pixel array images a scene with low contrast. Connectivity of the differential input stage allows the ramp signal to see a constant capacitive load thus reduce image artifacts referred to as smear.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.