High frequency equivalent circuit of GaAs depletion and enhancement FETs for large signal modelling

Abstract

For the design of digital circuits as well as for power amplifiers, the nonlinear modelling of GaAs FETs is a necessity. We use an extended equivalent circuit, which takes into account the gate current of positive biased transistors as well as the symmetrical nature of the devices at low drain voltages. A fast method to determine the elements of the equivalent circuit from measured S-parameters is presented which delivers for the first time good agreement for all operating points. A valid large signal description of the device can be obtained by implementing the bias dependences of the intrinsic elements into a circuit simulator like SPICE.