Analog to digital converters for CMOS imagers

A/D converters for single chip CMOS imagers have often been designed using the column-parallel approach, employing a slow A/D converter for each column of the sensor array. This thesis investigates a serial approach utilizing a single fast A/D converter to process all of the imager pixels. If power scales linearly with frequency in a given A/D architecture, power dissipation for the two approaches should be comparable. However, the serial approach should occupy less area since only the cost of one A/D converter is incurred. A figure of merit 1/power*area is introduced to verify this theory by comparing previously reported A/D approaches after appropriate technology, speed, and supply scaling. Camera system specifications require a single serial A/D converter to have 10b resolution at a 3MHz sampling rate for a CIF (352x288) imager array running at 30 frames/second Area minimization, power minimization, and the ability to build the A/D in a standard CMOS process are extremely important for consumer product applications. A single slope A/D architecture with a subnanosecond time digitizer shows promise for optimizing figure of merit over pipelined and folding interpolating approaches. This work focuses on the design issues of the 3MHz single-slope based A/D converter. Architectures appropriate for extending this A/D converter to 12MHz for four times CIF image arrays (704x576) are discussed. The 3MHz converter was designed, simulated, and laid out in a 0.35um CMOS technology. At 3.3V supply, 25°C and nominal process conditions, the converter dissipates 29 mW while occupying 0.3 mm2 . A 12MHz trislope extension of this converter is estimated to dissipate 37 mW in 0.4 mm2.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

1998

Author dc:creator

• Dacy, Susan (Susan Mary), 1975-

Advisor dc:contributor.advisor

• Charles Sodini and Marc Loinaz.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/46276

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/46276