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Improved Complementary Metal Oxide Semiconductor Digital Pixel Sensor

Author(s): Chavan Y | Mishra D

Journal: IETE Journal of Research
ISSN 0377-2063

Volume: 55;
Issue: 5;
Start page: 222;
Date: 2009;
Original page

Keywords: ADCs | Active pixel sensor | Charge coupled device | Digital pixel sensor | i0 mage sensors | Passive pixel sensor.

Charge Coupled Devices (CCDs) are used in imaging as they have advantages over conventional bulky tube type TV cameras. The complementary metal oxide semiconductor (CMOS) based image sensors, passive pixel sensors (PPS), and active pixel sensor (APS) have advantages in implementation. This makes the APS competitive with CCDs. However, APS is not popular because of the poor fill factor and lack of resolution. With the development of image sensor technology, digital pixel sensor (DPS) has overcome all problems associated with CCDs and CMOS-APS image sensor. In DPS, comparator and memory are implemented on chip for each pixel. This results in benefits in terms of power, pixel size, fill factor and resolutions. This paper analyses earlier DPS pixel with an analog comparator and inverter-based comparator. The limitations reported in the analysis of analog comparator are overcome using cascaded CMOS inverter-based comparator. The cascaded CMOS inverter is built with proper adjustment of Width (W) to Length (L) ratio. This adjustment sets the threshold voltage ′V th ′ that remains fixed for the pixel (in our case V th is equal to 2.2V). This cascaded inverter based comparator is called as threshold inverter quantizer (TIQ) and is further analyzed with biasing for high gain. Four-pixel and 16-pixel array design is done using TIQ based pixel. Extensive simulation of the TIQ based pixel array is done and results are reported for current and power dissipation.
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