On the Mechanisms of Linearity Peak Modeling in Common-Emitter SiGe HBTs Using Mextram 505

This paper presents detailed mechanisms of how improved intrinsic collector-base junction depletion capacitance (Ctc) model in Mextram 505 improves OIP3 peak modeling in common-emitter SiGe HBTs. Harmonics of individual branch currents are examined using custom Verilog-A codes. Interestingly, the third order Ctc charging current is found to be much lower than the third order main current (IN), which dominatesthe third order collector current. Early effect is further excluded as the reason for improved third order current modeling. Circuit level propagation of nonlinear Ctc current towards IN is concluded to be the main mechanism by which IP3 peak behavior is improved in Mextram 505.