While trying to analyze the effect of PA bias on the linearity aspects of power amplifier, I came across an analytical model of a BJT amplifier. It is known as the Gummel Poon model.  A quick Wikipedia check on the history suggests that, the model is about 40 years old. I need to figure out the model in detail. I am not sure how good they are as a model equivalent for a cmos. In any case I reckon this may be useful to analyze things such as RF power amplifier nonlinearity?