An Active Pixel CMOS Separable Transform Image Sensor

This paper presents a 128 x 128 charge-mode CMOS imaging sensor that computes separable transforms directly on the focal plane. The pixel is a unique extension of the widely reported Active Pixel Sensor (APS) cell. By capacitively coupling across an array of such cells onto switched capacitor circuits, computation of any unitary 2-D transform that is separable into inner and outer products is possible. This includes the Walsh, Hadamard and Haar basis functions. This scheme offers several advantages including multiresolution imaging, inherent de-noising, compressive sampling and lower integration voltage and faster readout. The chip was implemented on a 0.5 mu m CMOS process and measures 9mm(2) in MOSIS' submicron design rules.