An amplifier's datasheet noise density predicts a single-reading standard deviation…
PHYSICS · Subjective · Fermi University Physics · Electronics, Instrumentation & Communication · Feedback, operational amplifiers and analogue signal processing · Feedback, operational amplifiers and analogue signal processing
Inside the Instrument, Ch Low-noise front ends and noise measurement
Problem
An amplifier's datasheet noise density predicts a single-reading standard deviation of 20μV in the band used. A researcher averages M=100 successive readings and measures a standard deviation of 18μV, barely smaller than before. They conclude: "the amplifier must be noisier than its datasheet states, since averaging has not helped much; we will simply average over more readings." Find the error in this reasoning and say what should be checked instead.