Analog VLSI signal processing: Why, where, and how?

Analog VLSI signal processing is most effective when precision is not required, and is therefore an ideal solution for the implementation of perception systems. The possibility to choose the physical variable that represents each signal allows all the features of the transistor to be exploited opportunistically to implement very dense timeand amplitude-continuous processing cells. This paper describes a simple model that captures all the essential features of the transistor. This symmetrical model also supports the concept of pseudo-conductance which facilitates the implementation of linear networks of transistors. Basic combinations of transistors in the current mirror, the differential pair and the translinear loop are revisited as support material for the description of a variety of building blocks. These examples illustrate the rich catalogue of linear and nonlinear operators that are available for local and collective analog processing. The difficult problem of analog storage is addressed briefly, as well as various means for implementing the necessary intrachip and interchip communication.