This paper presents fundamentals of SiGe HBT RF linearity and its compact modeling using Mextram 504.12 and the latest Mextram, 505.00, for both common-emitter and common-base configurations.Collector-base junction depletion capacitance model is shown to be significant for accurate modeling of peak IP3 behavior, for which two new options are introduced in Mextram 505.00.Current dependence of avalanche factor is shown to be important for accurate modeling of IP3 peak. This is increasingly important in emerging RF applications requiring SiGe HBTs to operate at increasingly high VCB with negative IB .

This paper presents an X-parameter based approach to characterizing and compact modeling of SiGe HBT linearity. Removing RF source distortion using X-parameter measurements significantly increases measurement accuracy in highly linear common-base SiGe HBTs. X-parameters simulated using Mextram 505.0 are compared with measurements for the first time. To a large extent, our model accurately captures nearly all the X-parameters for a large range of biasing emitter current and collector-base voltage.

This paper examines parasitic PNP transistor current modelingin a high voltage bipolar transistor operating at high injection.We show that current parasitic PNP models are far from sufficient and propose a new model based on the epi-layer model of Mextram.The model is implemented in a development version of Mextram and demonstrated to fit well measured substrate current.

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.

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