Vision processing is a topic traditionally associated with neurobiology; known to encode,
process and interpret visual data most effectively. For example, the human retina;
an exquisite sheet of neurobiological wetware, is amongst the most powerful and efficient
vision processors known to mankind. With improving integrated technologies, this has
generated considerable research interest in the microelectronics community in a quest to
develop effective, efficient and robust vision processing hardware with real-time capability.
This thesis describes the design of a novel biologically-inspired hybrid analogue/digital
vision chip ORASIS1 for centroiding, sizing and counting of enclosed objects. This chip is
the first two-dimensional silicon retina capable of centroiding and sizing multiple objects2
in true parallel fashion. Based on a novel distributed architecture, this system achieves
ultra-fast and ultra-low power operation in comparison to conventional techniques.
Although specifically applied to centroid detection, the generalised architecture in fact
presents a new biologically-inspired processing paradigm entitled: distributed asynchronous
mixed-signal logic processing. This is applicable to vision and sensory processing applications
in general that require processing of large numbers of parallel inputs, normally
presenting a computational bottleneck.
Apart from the distributed architecture, the specific centroiding algorithm and vision
chip other original contributions include: an ultra-low power tunable edge-detection circuit,
an adjustable threshold local/global smoothing network and an ON/OFF-adaptive spiking
photoreceptor circuit.
Finally, a concise yet comprehensive overview of photodiode design methodology is provided
for standard CMOS technologies. This aims to form a basic reference from an engineering
perspective, bridging together theory with measured results. Furthermore, an
approximate photodiode expression is presented, aiming to provide vision chip designers
with a basic tool for pre-fabrication calculations.