An accurate quasi-saturation BJT model for very-high-frequency analog/digital applications

Abstract

An accurate quasi-saturation BJT model is proposed for very-high-frequency analog and digital applications. In modern low-power analog and digital circuits, the BJT often operates in a low collector voltage and high collector current region. Under such a quasi-saturation condition, base and collector resistances have nonlinear characteristics and the base pushout phenomenon occurs. However, these phenomena are not taken into the conventional small-signal model accurately, so that the collector current, the small-signal input impedance, and the small-signal current gain are overestimated under the quasi-saturation condition. We have developed linearized base and collector resistance models and the physically based base pushout model for accurate circuit simulations.