An Extended Dynamic Range Imaging by Selective Exposure Time Control for a Macro-Pixel Based CMOS Image Sensor in Machine Vision Application

Abstract

A CMOS image sensor capable of selectively varying each pixel's exposure time supported by modified X-Y addressing scheme and pixel sequential readout architecture to increase the intra-scene dynamic range for a macro-pixel which the focal plane is divided into is discussed. The proposed architecture provides finer granularity of exposure time control compared to our previous image sensor from a macro-pixel to a single pixel. As a result, a generation of under-exposure due to large illumination difference within a macro-pixel can be suppressed, which enables sophisticated high-level functionalities in machine vision application by scene recognition. We fabricated a test chip using 0.18-μm 1P5M standard CMOS process. In the chip, twelve 10-b 2.5MS/s pipelined Analog-to-Digital Converters (ADC) are integrated for on-chip digitization. The measurement results demonstrate high flexibility on extended dynamic range imaging, improved pixel fixed pattern noise and ADC-s differential non-linearity of +0.94/-1.38LSB.