Circuit models for analysis of intermodulation distortion in UHF bipolar transistors

Linear and nonlinear circuit models have been derived for UHF bipolar transistors. By modifying the high-frequency hybrid-pi model, a linearUHF transistor model was derived. Linear models were obtained for three types of transistors; these models were used to predict the S-parameters of the transistors. The predicted and measured values of the S-parameters were compared. Four sources of nonlinearity in the transistor were examined and characterised by polynomials which were expressed in terms of the voltages at the transistor junctions. By incorporating these nonlinearities into the linear model, a nonlinear UHF transistor model was derived. The nodal equations of this nonlinear model were successively solved by expressing each nodal voltage in terms of a Volterra series expansion of the input voltage. Based on this analysis, predictions of the intermodulation distortions in the three types of transistors were made these predictions were compared with in'e modulation measurements.