A Novel Approach for Parameter Determination of HBT Small-Signal Equivalent Circuit

Direct parameter extraction is believed to be the most accurate method for equivalent-circuits modeling of heterojunction bipolar transistors (HBT’s). Using this method, the parasitic elements, followed by the intrinsic elements, are determined analytically. Therefore, the quality of the extrinsic elements extraction plays an important role in the accuracy and robustness of the entire extraction algorithm. This study proposes a novel extraction method for the extrinsic elements, which have been proven to be strongly correlated with the intrinsic elements. By utilizing the specific correlation, the equivalent circuit modeling is reduced to an optimization problem of determining six specific extrinsic elements. Converting the intrinsic equivalent circuit into its common-collector configuration, all intrinsic circuit elements are extracted using exact closed-form equations for both the hybrid-π and the T-topology equivalent circuits. Additionally, a general explicit equation on the total extrinsic elements is derived, subsequently reducing the number of optimization variables. The modeling results are presented, showing that the proposed method can yield a good fit between the measured and calculated S parameters. key words: HBT’s, small signal modeling, T-topology, hybrid-π equivalent circuit