I have some fundamental questions about noise in op amps.
1. How does Analog Devices know that an op amp has noise?
I.e. how does AD determine or measure that any given op amp has a certain amount of voltage or current noise?
2. What does noise data look like?
I.e. Is it frequency domain just like in datasheets (e.g. nV/rtHz per log10 freq), is it a time-domain waveform for which RMS is calculated?
3. I am wondering what noise is. Are the current, voltage noises of an op amp aperiodic, Gaussian waveforms (with zero mean and standard deviation equal to their RMS values)? Do they appear in reality as a small fluctuating voltage on highly sensitive voltmeters or instruments?