Signal and Noise Time –domain Models for Microwave FETs

Abstract

Accurate characterization of active devices is one of the most crucial steps in efficient microwave circuit design. As the operating frequency increases, the dimensions of the electrodes of microwave transistors such as FETs become comparable to the wavelength, highlighting the parasitic effect of wave propagation and phase cancellation. Thus, this effect needs to be accurately evaluated in the device model to assure a reliable design. In this work, we proposed new small- and large-signal FET models for efficient millimeter-wave circuit design. In our approach, the device width was divided into an infinity number of segments, while each segment was considered as a combination of three coupled lines and a conventional FET equivalent circuit. By solving a set of multiconductor transmission line equations using the Finite-Difference Time-Domain (FDTD) technique, an accurate and efficient transistor modeling approach has been introduced. Furthermore, a new distributed noise FET model was proposed. It consists in a threecoupled excited transmission line (TL) structure in which the Laplace transformation was applied to determine the noise currents and voltages of lines. The structure was also analyzed by applying the Green's function concept as a wave approach. The proposed distributed mm-wave noise FET model has been demonstrated through successful comparison with measurements.