Simulation of the RF performance of AlGaAs/GaAs heterojunction bipolar transistors: application of fast Fourier transform

The results of a Fourier decomposition technique approach to simulate the small signal microwave performance of AlGaAs/GaAs heterojunction bipolar transistors are reported. For demonstration, a 1-D numerical simulation code is used to obtain the transient base and collector currents resulting from a small base-emitter voltage step superimposed on a DC bias. The frequency-dependent common-emitter current gain and associated phase shift are then determined by using the discrete fast Fourier transform technique. This approach gives the same accuracy as obtained by the traditional point-by-point method with the benefit of acquiring a wide range of frequency response with just one input signal waveform.