There are two models dedicated to bipolar transistors. Mextram is the model intended for use with vertical bipolar transistors (both NPN and PNP). Its intrinsic model is basically one-dimensional, but the the model includes descriptions for the extrinsic regions and for the substrate (the fourth terminal). The intrinsic model includes quite advanced descriptions for the collector epilayer and for modern SiGe transistors.

Modella is intended for use with lateral PNP transistors. Its basic description is less advanced, but it has unique features to describe the two-dimensional current spreading effects in lateral bipolar transistors.


The Mextram model gives an excellent description of vertical bipolar transistors in all kinds of processes, amongst which are modern SiGe processes and robust HV processes. It is very efficient in modelling the lowly doped collector epilayer of a bipolar transistor where effects like velocity saturation, base widening, Kirk effect, and impact ionisation play a role. Effects due to having Germanium in the base are also modelled. Furthermore, it contains a full description of the extrinsic regions of a transistor, including substrate current and capacitance. Mextram has formulations for temperature scaling and is easily scalable over geometry. Mextram, level 504, includes full self-heating, in contrast to having self-heating handled by the circuit-simulator. Self-heating is completely implemented in the source code. See More >


In the design of bipolar analogue integrated circuits, greater flexibility is often achieved when both NPN and PNP transistors are incorporated in the circuit design. Many present-day bipolar production processes use the conventional lateral PNP as the standard PNP transistor structures. For accurate modelling of such a lateral PNP transistor it is important to take the complex two-dimensional nature of the transistor into account. The physics based model Modella (MODEL LAteral) does exactly this, using a modelling approach whereby the main currents and charges are independently related to bias-dependent minority carrier concentrations. Current crowding effects, high injection effects, and a bias dependent output impedance are all taken into account. See More >