Design of CMOS-APS circuits for mixed image processing and analysis of their transfer characteristics

Abstract

CMOS APS Active Pixel Sensors (APS) are very important among others because of their possible technical innovations leading to ultra-low power image acquisition or efficient on-chip image preprocessing. The design of the novel CMOS is presented in the first part of the paper. The general principle of analog interpixel subtraction is described. The edge detection algorithm for analog realization and patented focal plane circuits for analog image preprocessing (signals subtraction, addition, and edge detection) are described. Implementation of the image processing tasks (focal plane preprocessing and subsequent image processing) can be done effectively only with the consideration of known transfer characteristics of the imager itself. In the second part of the paper we present analysis of those characteristics. Geometrical Point Spread Function (PSF) depends on the certain geometric shape of active area in the particular design of CMOS APS. In this paper the concept of Modulation Transfer Function (MTF) analysis is generalized to be applicable to the sampled structures of CMOS APS. Recalling theoretical results we have analytically derived the detector MTF in the closed form for some special active area shapes.