Design tradeoffs for improved VCE(sat) versus IC of bipolar transistors under forced gain conditions

Based on the quasi-saturation analysis of bipolar transistors and using numerical simulation, it is shown in this paper that the quasi-saturation performance of transistors under forced gain conditions can be improved by increasing the base-Gummel number if the emitter diffusion is also simultaneously altered to keep the active region current gain h_FEO constant. It is further shown that for a given h_FEO, if the ratio of h_FEO to the forced current gain β_f is below 10, the quasi-saturation performance of the transistors will be poor compared to those with h_FEO/β_f⩾10. Design curves obtained using numerical simulation are also presented to choose the quasi-saturation current limit of the transistors as a function of breakdown voltage and for different reach-through collector structures