Basic expressions and approximations in small-signal parameter extraction for HBT´s

Basic expressions and approximations used to extract small-signal parameters for heterojunction bipolar transistors or bipolar junction transistors are developed in this paper. A T-type small-signal equivalent circuit after deembedding the pad capacitances is used for the derivation. The relative magnitudes of ωR_bcC_be , ωR_biC_bc, and ωr_cC _bell were used to evaluate the frequency ranges. Fully numerical or partially numerical approaches can be developed by these approximations. An element parameter-extraction procedure is also given in this paper. Two special cases (“cold” bias and degrading equivalent circuits) are also discussed