Computing, Health and Science
School of Engineering and Mathematics
This paper presents a digital pixel sensor (DPS) array employing a time domain analogue-to-digital conversion (ADC) technique featuring adaptive dynamic range and programmable pixel response. The digital pixel comprises a photodiode, a voltage comparator, and an 8-bit static memory. The conversion characteristics of the ADC are determined by an array-based digital control circuit, which linearizes the pixel response, and sets the conversion range. The ADC response is adapted to different lighting conditions by setting a single clock frequency. Dynamic range compression was also experimentally demonstrated. This clearly shows the potential of the proposed technique in overcoming the limited dynamic range typically imposed by the number of bits in a DPS. A 64 × 64 pixel array prototype was manufactured in a 0.35-μm, five-metal, single poly, CMOS process. Measurement results indicate a 100 dB dynamic range, a 41-s mean dark time and an average current of 1.6 μA per DPS.