Design techniques for GaAs MESFET switches

A three-port bias-dependent model for a switch FET is presented. The importance of a three-port model is highlighted, and the large-signal behavior of a MESFET switch in its ON and OFF states is discussed. The effect of gate bias resistance and bias potential is illustrated. Simple equations and techniques are presented which enable estimates of power performance of complex switches to be made prior to detailed nonlinear analysis. Specifically, the models provide circuit designs with the ability to estimate large-signal power-handling characteristics of MMIC (monolithic microwave integrated circuit) switch designs, without immediate recourse to complex nonlinear computer-aided design. Expressions which allow 1-dB compression points to be estimated are given and verified by comparison with measurements of two switch FETs. Finally, the isolation performance at large signal levels is discussed.<>