Asymemetry in intermodulation distortion of HBT power amplifiers

This work demonstrates the prediction of asymmetry in intermodulation distortion of HBT power amplifiers under two-tone excitation. While previous predictions were based on Volterra series in conjunction with a simple device model, the present approach is based on harmonic-balance simulation in conjunction with a nonlinear large-signal device model. The present approach is validated by the agreement between simulations and measurements under different bias, matching and input conditions as well as tone separations. The present result is consistent with the Volterra-series analysis of the effect of baseband termination impedance on the intermodulation asymmetry.