Use of the transistor as a switch in precise analogue¿digital-convertor circuits

The transistor can be used as a switch, but its operating characteristic departs from the ideal by having a finite leakage current when open and an effective contact potential when closed. These effects, and the limitations they impose in use with precise analogue-digital convertors, are discussed. Types of circuit in which the transistor can be used are described, and it is suggested that it is possible to achieve a resolution and accuracy, when using the transistor switch, comparable with those obtainable with a conventional potentiometer.