An integrated FET analog switch

Abstract

The use of a field-effect transistor as the basic switching element permits the design of integrated analog switches with extremely low offset-voltage and good isolation from ground. The static behavior of an FET as an analog switch is described by its on-impedance and its off-leakage current. The switching speed is limited by capacitive coupling between the gate and the channel of the FET. A figure of merit for chopper FET's relates the resulting transients on the signal line to basic design parameters. Design considerations for a driving circuit are presented. The use of such advanced techniques as multiple epitaxial deposition leads to a monolithic structure which optimizes the field-effect transistor as well as the elements of the driving circuitry. The resulting device, integrated on a 0.06-inch×0.06-inch silicon chip, compares favorably with conventional analog switches.