DocumentCode :
1476888
Title :
A Nyquist-rate pixel-level ADC for CMOS image sensors
Author :
Yang, David X D ; Fowler, Boyd ; El Gamal, Abbas
Author_Institution :
Inf. Syst. Lab., Stanford Univ., CA, USA
Volume :
34
Issue :
3
fYear :
1999
fDate :
3/1/1999 12:00:00 AM
Firstpage :
348
Lastpage :
356
Abstract :
A multichannel bit-serial (MCBS) analog-to-digital converter (ADC) is presented. The ADC is ideally suited to pixel-level implementation in a CMOS image sensor. The ADC uses successive comparisons to output one bit at a time simultaneously from all pixels. It is implemented using a 1-bit comparator/latch pair per pixel or per group of neighboring pixels, and a digital-to-analog-converter/controller shared by all pixels. The comparator/latch pair operates at very slow speeds and can be implemented using simple robust circuits. The ADCs can be fully tested by applying electrical signals without any optics or light sources. A CMOS 320×256 sensor using the MCBS ADC is described. The chip measures 4.14×5.16 mm2. It achieves 10×10 μm2 pixel size at 28% fill factor in 0.35 μm CMOS technology. Each 2×2 pixel block shares an ADC. The pixel block circuit comprises 18 transistors. It operates in subthreshold to maximize gain and minimize power consumption. The power consumed by the sensor array is 20 mW at 30 frames/s. The measured integral nonlinearity is 2.3 LSB, and differential nonlinearity is 1.2 LSB at eight bits of resolution. The standard deviation of the gain and offset fixed pattern noise due to the ADC are 0.24 and 0.2%, respectively
Keywords :
CMOS image sensors; analogue-digital conversion; mixed analogue-digital integrated circuits; video cameras; 0.35 micron; 20 mW; A/D convertor; CMOS image sensors; Nyquist-rate ADC; analog-to-digital converter; comparator/latch pair; multichannel bit-serial ADC; pixel-level ADC; sensor array power consumption; subthreshold operation; successive comparisons; Analog-digital conversion; CMOS image sensors; CMOS technology; Circuit testing; Digital control; Latches; Optical sensors; Pixel; Robustness; Sensor arrays;
fLanguage :
English
Journal_Title :
Solid-State Circuits, IEEE Journal of
Publisher :
ieee
ISSN :
0018-9200
Type :
jour
DOI :
10.1109/4.748186
Filename :
748186
Link To Document :
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