Quote:
Originally Posted by 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.
David
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I can see your point about the nodes.
Also I can see, that in Cascode, that one could regard the upper device as a grounded grid or grounded base amplifier, with the signal drive to it being equal to the input signal to the lower device (but inverted) applied to the emitter or cathode; then the circuit voltage gain with that reasoning, could be attributed to the upper device.
But it is interesting that the upper device could be completely removed, allowing the plate voltage of the lower device to move around, with no great overall change in the voltage gain (at low frequencies where Miller effect wasn't dominant). So I find it difficult, viewing the circuit as a working whole, to ascribe its voltage gain to the upper device, even though that is a reasonable way of looking at it too.