Consider two currents

PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Feedback, operational amplifiers and analogue signal processing · Feedback, operational amplifiers and analogue signal processing

Inside the Instrument, Ch Noise sources and amplifier noise

Problem

Consider two currents, both equal to 2 mA2\,\mathrm{mA}: (i) a current through a 1 kΩ1\,\mathrm{k}\Omega metal-film resistor, and (ii) a current flowing across a forward-biased silicon diode junction. ((a)) Which of the two currents carries full shot noise, and why does the other not? ((b)) An operational amplifier is wired as an inverting amplifier with R1=10 kΩR_1 = 10\,\mathrm{k}\Omega from the source to the inverting input and R2=10 kΩR_2 = 10\,\mathrm{k}\Omega feedback resistor, giving a closed-loop signal gain of −1-1. A technician argues: "Since the signal gain is −1-1, the amplifier's own input voltage noise ene_n is amplified by a factor of 1 at the output." State the correct noise gain of this stage and explain the technician's error.

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