6.5 THE FBH HBT MODEL

The FBH Model [18] was developed by the author at the Ferdinand-Braun-Institut fur H chstfrequenztechnik, in Berlin, Germany. Its primarily goal was to facilitate the design of monolithic integrated microwave circuits (MMICs) in GaAs-HBTs. It is, however, versatile enough to also describe InP-based HBTs.

The philosophy behind the model is that while all of the issues addressed in Chapter 2 should be taken care of, the model should at the same time be based on easy-to-understand formulas with easy-to-extract parameters. Therefore, its basic structure was based on the Gummel-Poon model, with extensions and improvements as required.

The FBH HBT model features:

• Early and Webster effects (borrowed from VBIC);

• Nonideal base currents (base-emitter and base-collector);

• Self-heating and thermal interaction (by a thermal port);

• Continuously differentiable depletion capacitance;

• Unified description of transit time and collector capacitance variation due to velocity modulation;

• Excess transit time due to base pushout, borrowed from HICUM;

• Base-emitter and base-collector breakdown;

• Enhanced noise model: improved in the 1/ f range as well as in the RF range;

• Scaling with transistor size.

The equivalent circuit of the FBH HBT model is shown in Figure 6.10 and its parameters are listed in Table 6.9.