philips said:
Gain is usually V2/V1, but sometimes it's I2/I1, or even V2/I1
(also known as Z21) I was simply wondering when it is appropriate
for gain to be V2/V1 or I2/I1 etc i.e. is it more informative
to talk about voltage gain than current gain, is it hourses for
courses?
It depends on what is important in the circuit. If it is a signal
amplifier and the signals are represented by voltages (as in common
with audio) and input impedance is assumed to be much higher than the
impedance of the source feeding the stage, and the output impedance of
the stage is much lower than its load, voltage gain is the natural way
to look at the stage. If the stage is an RF gain stage that needs to
match source and load impedances, then voltage gain and current gain
are related by the pair of impedances, so voltage gain, current gain ,
Vout/Iin, Iout/Vin, or most useful, PowerOut/PowerIn are all
reasonable. If the voltage gain is nearly 1 as with all followers,
voltage gain is not nearly as useful a way to describe the stage as
current gain.
Am I addressing your question or did it go right by me?