Transistors

[Kalee20]

Maybe I should modify my assertion to say that a bipolar transistor without any external feedback is fundamentally a current amplifier.

Even a common base stage will be horribly non-linear if fed from a voltage source (ie a low impedance).
Adding a series resistance to the input will reduce the non-linearity but then the resistor is effectively a voltage to current converter.

To generalise for a common emitter transistor, adding external negative feedback can stabilise either the current or voltage gain as desired.

To stabilise the voltage gain add an emitter resistor (series derived series feedback), the limiting case for this is the emitter follower with 100% voltage feedback. (not 100% voltage gain).
To stabilise the current gain add a resistor from collector to base (shunt derived shunt feedback), the limiting case for this is common base with 100% current feedback. (not 100% current gain).

A transistor's fundamental operating mode has to be common-base, in terms of internal workings. Current in, current out. (A valve's fundamental is common-cathode, voltage in, current out).

If you connect it in the 'most useful' configuration - common emitter - then it is best to think of it as a black box and not be too bothered about what goes on internally.

And in common-emitter, sometimes I think of it as current-operated (when used as a switch in logic circuits) or as voltage-operated (when used as an amplifier). As the switch, as long as given zero base current, it's 'off'' and as long as given sufficient, it's 'on'. As the amplifier, the input resistance is as ill-defined as beta is - so you have to design such that the effects are negligible.

As for a common-emitter amplifier with emitter degeneration ending up in a limiting case as an emitter follower, I have to disagree! Because raising the emitter resistor more and more drops the gain to the collector to less and less, ending up as zero. To get to the emitter follower, you have to make a step change to the output connection. The same goes for common-emitter with shunt feedback, yes the transresistance is stabilised (ratio of output voltage to input current), but again, to get to a common-base configuration you have to reconfigure the circuit - you can't get there by smoothly altering resistors to zero or infinity.