An accurate bipolar model for large signal transient and ac applications

It is shown that models employing only two ac parameters can be accurate, at best, to first order in frequency. A new small signal model is presented, and it is demonstrated by comparison with exact results that only three ac parameters are sufficient to maintain model accuracy at much higher frequencies than achieved by any previous model. (At and below the unity gain frequency, ωT, the maximum magnitude error is 2% and the maximum phase error is 1.1°.) Analytic expressions are given for the 3 parameters. The validity of the charge sharing scheme of Ref. 1 is established. A large signal model is presented which can be easily and efficiently incorporated into the existing SPICE Gummel-Poon model.