All-Digital, CMOS-Based Photodiode Camera

CCDs (Charge-Coupled Devices), and more recently, CMOS (complementary-symmetry metal-oxide-semiconductor) APS (Active Pixel Sensor) cameras have revolutionized imaging instrumentation and the many fields that utilize these instruments. Both these technologies rely on integrating, the analog photo-current generated in each pixel, which limits their sensitivity and bandwidth. Counting individual optical photons with an avalanche photodiode operated above its breakdown voltage provides the greatest sensitivity, and represents true digital imaging that facilitates pixel-level signal processing. In essence, the Geiger APD pixel directly converts an incident photon flux into a digital count rate, which eliminates the readout noise associated with analog detection, providing a unique CMOS architecture for analog-to-digital conversion. This program develops a fully integrated, digital camera chip, which is an application specific integrated circuit (ASIC) that counts individual optical photons using avalanche photodiodes operated above breakdown, in Geiger mode. This all-digital, CMOS imaging technology fulfills the demanding requirements for providing high-resolution images at GHz speeds characteristic of CMOS devices. In Phase I, we successfully completed all the Phase I goals by designing, fabricating, and characterizing the Geiger APD pixel elements of the APS camera ASIC. In Phase II, we will design, fabricate and characterize prototypes of the complete APS camera ASIC.