Exponential and logarithmic functions using standard CMOS 0.8 mu m technology

The integration of various mathematical functions in an analogue mode is a growing concern, e.g., for image processing applications. Specific cells us ing CMOS technology which perform arithmetical operations [1,2] have alread y been designed. This paper describes an extension of the previous cells pe rforming the two most fundamental transcendental functions: logarithm and e xponential. The design of this extension and technological issues are detai led in this paper. The exponential function is based on MOS transistors ope rating in the weak inversion region, in order to behave like bipolar transi stors while remaining in a standard CMOS technology.