Time domain modeling of nonlinear BJT amplifiers using frequency domain analysis

In this paper, a novel approach to characterize the performance of nonlinear BJT amplifiers biased under large-signal condition is presented. The nonlinear element of the active device is modeled by a simple nonlinear device model. Frequency domain techniques are employed to relate the input impedance, the output impedance and the output power of a transistor to the input and the output current. Experimental results obtained from an implemented amplifier confirmed the validity of the theory. The discrepancy between measured and calculated output power was less than 1 dB. This verified that the non-linear device model was suitable to analyze nonlinear circuits such as high power amplifier, high power oscillator etc. at higher frequency.