Using Delta-Sigma Modulation for Sensing in a CMOS Imager

Publication Date

10-2008

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Electrical Engineering

Department

Electrical and Computer Engineering

Supervisory Committee Chair

R. Jacob Baker

Abstract

CMOS Image Sensors are used in a wide variety of applications today, including digital still cameras, video cameras, cellular phones, applications for car sensors (including back up cameras), and many other products. The majority of CMOS image sensors use a pipeline analog-to-digital converter (ADC) to turn an analog voltage, produced from light incident on a pixel, into a digital signal. This research explores the benefits of using delta-sigma modulation for column parallel sensing in lieu of a traditional analog scheme using a pipeline ADC. The benefits include an increase in signal to noise ratio (SNR), low power circuits, a small layout area, fast design times, and circuits that are easy to design for higher speeds. Results, obtained from a test chip fabricated using the AMI 500 nm process, are presented. Running at a clock rate of 100 MHz with a 20 us row sense time gives a resolution of 10 Bits. At this rate, a 2000 column imager will output a pixel every 10 ns.

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