Extended charge-control model for bipolar transistors

In modeling bipolar transistors the charge-control concept provides a means to predict dynamic behavior from a detailed knowledge of the steady state. As such, it is a first-order approximation lacking accuracy. It is shown that a considerable improvement can be obtained when the concept is extended by allowing time delays in the relations between controlling charges and terminal voltages and currents. It suffices to introduce two delays whose magnitudes can be determined or estimated from the steady-state solution. The increased range of validity of the extended charge-control model is demonstrated in detail, by confronting it with a rigorous model and comparing small-signal parameters.