Improved Compact Modeling of SiGe HBT Linearity With MEXTRAM

We compare measured and simulated RF third-order distortion current, as well as the corresponding IP3, as a function of bias, for a SiGe heterojunction bipolar transistor (HBT), using MEXTRAM. The collector-base (CB) depletion capacitance model is identified to limit IP3 modeling accuracy near its peak. New CB capacitance modeling options are developed to significantly improve high-current IP3 modeling accuracy, particularly its peak behavior. Guidelines to simultaneous fitting of f
_T
, f
_max
, IP3, and C
_BC
are developed.