Bipolar devices also have a capacitance that acts like Cgs of a FET; you can calculate it Cpi = (1/2piFt)*(Ic/Vt) where Ft is the transition frequency of the transistor (you might be able to find this in its data sheet), Ic is the collector current, and Vt is the thermal voltage, about 25 mV at room temp and increasing proportional to temperature.
So an interesting result is, if you have a 50 MHz Ft bipolar device with 1 ampere of current flowing in it, at room temperature, the capacitance you have to control is about 127 nF. This is the equivalent of a lot of FETs.
capslock said:This makes more sense to me, but I'll have to think about it. Why would one worry about C_BE? After all, it is more like a bootstrap, isn't it? And it might be the cause for local oscillations.