Circuit Model For GaAs MESFET As An Optical-microwave Interface

The use of a G A S MESFET as the interface between optical and microwave components, especially in MMICs (where it is the dominant active component), is discussed. This paper explains the optical response mechanisms in MESFETs and presents a circuit model based on the physical behaviour of the device under optical illumination. Measurements for the MESFET I/V characteristics over a wide bias voltage range and under both dark and illumination conditions are reported. The model for the GaAs MESFET under optical illumination was implemented into the circuit simulation program, PSpice, and simulation results are presented. The simulated results are shown to compare favourably with experimental measurements. Circuit models such as this would be desirable in the design ofoptically interfaced MMICs.