ABSTRACT
This chapter presents analogue switching using CMOS gates and how well they can be made to work, and examines why anyone should wish to perform the same function with discrete FETs. The JFET types J111 and J112 are specially designed for analogue switching and are pre-eminent for this application. It is possible to cascade FET switches, which is taken from a real application. The shunt FET is connected to ground via a blocking capacitor to prevent DC gain changes. In designing a mute bloc, people want low distortion and good offness at the same time, so the series-shunt configuration, which proved highly effective with CMOS analogue gates, is the obvious choice. The basic JFET shunt switching circuit's great advantage is that the depletion JFET will be in its low-resistance before and during circuit power-up, and can be used to mute switch-on transients. Soft changeover circuit is designed to give a soft changeover between two inputs, in effect a fast cross-fade.
