Simultaneous extraction of the small-signal equivalent circuit elements and noise parameters of HBTs

Abstract

A method for a reliable characterization of the small-signal equivalent circuit and the noise model of Heterojunction Bipolar Transistors (HBTs) is presented. It allows the device equivalent circuit elements (in T-topology) and its noise parameters (NPs) to be extracted simultaneously, using only the measurements of its S-parameters and its noise figure (measured for a well-matched impedance). The procedure is based on a simultaneous estimation of the device S-parameters and noise figure, by fitting to the corresponding measurements. The NPs estimated from the device model are compared to the NPs estimated from the measured noise figure, providing an additional term in the error function to be minimized that guarantees physical results. Thus, the error function is composed by three terms: the root-sum of squares (RSS) of the differences between measured and estimated S-parameters, noise figure and NPs, respectively. Experimental verification of the extraction of the equivalent circuit elements and NPs of an HBT, up to 8 GHz, are presented, and the NPs are compared to those measured with an independent (tuner-based) method.