What minimum CMRR in dB is required to keep common-mode error below the signal when Vcm = 1 V and Vdiff = 10 mV?

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Multiple Choice

What minimum CMRR in dB is required to keep common-mode error below the signal when Vcm = 1 V and Vdiff = 10 mV?

CMRR measures how much of a common-mode input sneaks into the output compared with the desired differential signal. To keep the common-mode error from swamping the measurement, the output due to the common-mode voltage must be smaller than the output due to the differential signal.

Let Ad be the differential gain and Ac the common-mode gain. CMRR = Ad/Ac. The differential output is Ad × Vdiff, while the unwanted common-mode output is Ac × Vcm. Requiring Ac × Vcm < Ad × Vdiff gives Ad/Ac > Vcm/Vdiff.

Here Vcm = 1 V and Vdiff = 10 mV, so Vcm/Vdiff = 100. Thus the CMRR must be greater than 100, which is 20 log10(100) = 40 dB. Therefore, the minimum CMRR is 40 dB.

What minimum CMRR in dB is required to keep common-mode error below the signal when Vcm = 1 V and Vdiff = 10 mV?

Prepare for the Instrumentation Controls Lab (EE2327L) Exam with our comprehensive resources. Study with interactive quizzes, detailed explanations, and practice questions. Master the fundamentals of instrumentation and controls to excel in your exam!

What minimum CMRR in dB is required to keep common-mode error below the signal when Vcm = 1 V and Vdiff = 10 mV?

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