Improved compact modeling of output conductance and cutoff frequency of bipolar transistors

The collector epilayer is a crucial element in the behavior of modern bipol ar transistors. Compact models for its description, like the Kull model, ar e therefore of crucial importance too. We give a Mextram-based improvement to these models for quasi-saturation and show that the output conductance a nd the cutoff frequency are less abrupt in this region. Apart from ohmic qu asi-saturation, we also include quasi-saturation due to the Kirk effect, wh ich results from velocity saturation.