A difference amplifier measuring a biological signal is exposed to of common-mode…

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

Electronics for Measurement, Ch The operational amplifier and negative feedback

Problem

A difference amplifier measuring a biological signal is exposed to

15\,\mathrm{mV}

of common-mode mains pickup at both inputs. Its own common-mode rejection ratio is

\mathrm{CMRR} = 90\,\mathrm{dB}

(a ratio of differential gain to common-mode gain, in decibels using

20\log_{10}

). ((a)) Convert the

90\,\mathrm{dB}

figure to a plain ratio. ((b)) Calculate the residual error this common-mode voltage produces, referred to the input.

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