Hybrid Small-Signal pi-Model for the Lateral NQS Effect in SiGe HBTs

The state-of-the-art and pi-models for the lateral non-quasi-static (NQS) effect are analyzed. The superiority of the pi-model to capture the lateral NQS effect is demonstrated through small-signal simulations of both the models, implemented in Verilog-A. A hybrid model is proposed and a corresponding formulation of the base impedance is obtained. The equation gives the base impedance of the state-of-the-art as well as the pi-model under appropriate conditions. The methodology to implement the hybrid model in Verilog-A is discussed. The hybrid model shows significantly higher accuracy than both the state-of-the-art model and the pi-model when compared with the device simulation data.