A JFET Circuit for Instrumentation Applications

A new class of junction field-effect transistor (JFET) circuit is introduced, which can serve as a simple versatile building block in instrumentation applications. Economical realizations of current-to-voltage converters, voltage-controlled voltage sources, and voltage-controlled current sources are described. The basic circuit building block, called the piggy-back pair, consists of a matched pair of JFET's and two resistors. The basic configuration is easily manipulated to realize various circuit functions when combined with a few other components. It is shown that by full utilization of the terminal properties of JFET's, many simple high-performance circuits can be designed, which have circuit functions determined essentially by resistor ratios and which accordingly are relatively insensitive to device parameters. The circuit design procedure is very straightforward with design limitations clearly indicated. The flexibility and versatility of the piggy-back pair is indicated by the wide range of circuits demonstrated.