ABSTRACT
Complementary mixed oxide semiconductor (CMOS) imagers, which have a large number of applications, have become a mainstream technology. Since the first CMOS imagers in the mid-1980s, CMOS imager pixels have evolved from a very simple dynamic random access memory (DRAM)-like architecture along a variety of different paths. The majority of CMOS imager products today employ a four-transistor pixel or one of its simple variants. Pixel architecture evolved first for optical performance, then to accommodate shrinking pixel sizes, and now for higher functionality. This chapter describes the evolution of the CMOS imager pixel circuit, gives a detailed description of the operation of the CMOS imaging pixel, and discusses issues that were encountered as the size of the pixel shrunk. Even though the CMOS imager technologies were cheaper and more adaptable, competition with the prior technology, and charge-coupled device (CCD) image sensors forced advances in the technology to improve the quality of the captured images.
