I'm a uni student trying to figure out how to calculate gains of op-amps with recorded real AC voltage inputs and outputs. We are expected to somehow know this for some post-lab work without being told how to do it in any of the lectures.
I'm assuming the gain is still defined as \$ v_{\mathbb{out}}/v_{\mathbb{in}} \$, which would mean the gain would vary of time. I know what the period, peak-to-peak voltages, and crest and trough input and output voltages are. Where do I go from here?
EDIT: By "real AC voltage" I mean actual AC voltages produced and recorded in a laboratory with real circuits; not hypothetical AC voltages with ideal circuits.
Best Answer
HarrisonO - I suppose, I know what you really mean. (By the way, what in your opinion is a "real" AC voltage?).
My answer: No - the gain is not varying with time. For AC signals it makes no sense to find the ratio Vout/Vin for momentary values of both signals. Instead, the gain is defined for mean values of the sinusoidal signals - more correct: For "root mean square rms" (magnitude ratio).
This applies to all amplifiers - single BJT stages or opamps, which in all cases are operated with signal negative feedback (and not open-loop). Because all amplfiers contain reactive elements, it is - in addition - common practice not only to calculate (or simulate) the magnitude ratio but also to find the phase shift between input and output.
The existence of a frequency-dependent phase shift is another argument against the usage of momentary values for finding the gain.