Document Type

Conference Proceeding




Faculty of Computing, Health and Science


School of Engineering and Mathematics




This is an Author's Accepted Manuscript of: Bermak, A. (2002). A CMOS Imager with PFM/PWM Based Analog-to-digital Converter. Proceedings of 2002 IEEE International Symposium on Circuits and Systems. (pp. IV-53 - IV-56 vol.4 ). Arizona, USA. IEEE. Available here

© 2002 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.


An on-pixel analog-to-digital converter based on both PFM and PWM schemes is reported. The proposed architecture uses a limited number of transistors that can be implemented in a small silicon area resulting in a 23% fill-factor. The digital sensor can be externally configured in order to operate under either the PFM or PWM scheme. At high light intensities, the PFM scheme is replaced by the PWM scheme which proves to be much more efficient in terms of power consumption and clock frequency requirements. An in-built light adaptation mechanism has also been implemented which allows the sensor to better adapt to low-light intensity or to adjust the sensor saturation level. As a consequence, the sensor features a programmable dynamic range. Image lag is reduced in both schemes since a reset of the photodetector is performed after the conversion period. The pixel based ADC has been designed and fabricated using CMOS 0.25 μm technology.



Access Rights


Included in

Engineering Commons


Link to publisher version (DOI)