TRANSLINEAR CIRCUITS IN SUBTHRESHOLD MOS

In this paper we provide an overview of translinear circuit design usi ng MOS transistors operating in subthreshold region. We contrast the b ipolar and MOS subthreshold characteristics and extend the translinear principle to the subthreshold MOS ohmic region through a drain/source current decomposition. A front/back-gate current decomposition is ado pted; this facilitates the analysis of translinear loops, including mu ltiple input floating gate MOS transistors. Circuit examples drawn fro m working systems designed and fabricated in standard digital CMOS ori ented process are used as vehicles to illustrate key design considerat ions, systematic analysis procedures, and limitations imposed by the s tructure and physics of MOS transistors. Finally, we present the desig n of an analog VLSI ''translinear system'' with over 590,000 transisto rs in subthreshold CMOS. This performs phototransduction, amplificatio n, edge enhancement and local gain control at the pixel level.