[Radio Wrangler]

There are more than two nodes moving in voltage, therefore there are more than one transfer functions or gains at play

The transfer function of the bottom device base voltage to the upper device collector in a cascode circuit is the overall gain of the amplifier. This is of interest because it is what the circuit is required to achieve.

The transfer function of the bottom device base to the bottom device collector (== top devive emitter) is also of interest because this is the particular gain which sets the amount of Miller effect and thus dominantly controls the upper limit of the frequency response of the whole amplifier. It may not seem like an interesting node because we are not doing anything with it, but it is certainly doing things with parameters affecting the nodes we are using.

David