Distortion in high-frequency FET amplifiers

A high-frequency nonlinear model of FET´s is developed in which all sources of nonlinearities, including the output conductance, are accounted for. The distortion resulting from this model is represented using the Volterra series approach, and a high degree of accuracy between the theory and the measured results is obtained. Although the theory holds only for circuits that exhibit a slight deviation from linearity, it is found that fairly good agreement exists at larger signal levels. Harmonic, intermodulation, and cross-modulation distortion (CMD) that occur in a typical high-frequency single-stage FET amplifier are all analyzed and experimentally verified. It is observed that the CMD that occurs in the FET under consideration is of the AM type.