What is a practical consequence of poor CMRR in an instrumentation amplifier?

What is a practical consequence of poor CMRR in an instrumentation amplifier?

• A. Increased sensitivity to common-mode noise, leading to reduced differential accuracy.
• B. Reduced open-loop gain but no change in differential accuracy.
• C. Increased bandwidth with no negative effects.
• D. No practical consequence in typical circuits.

Answer: (A)

Common-mode rejection ratio tells us how well an instrumentation amplifier suppresses signals that appear the same on both inputs. If CMRR is high, the output reflects mainly the difference between the inputs, with little influence from anything that both inputs see equally (like power-line hum, EMI, or ground noise). When CMRR is poor, part of that common-mode voltage leaks into the output as if it were part of the signal, so the amplifier shows more noise and error in the differential measurement. In other words, common-mode noise becomes differential at the output, reducing differential accuracy. The other statements don’t capture this effect: CMRR isn’t a direct measure of open-loop gain or bandwidth changes, and there is a practical consequence in real circuits when common-mode leakage occurs.

Common-mode rejection ratio tells us how well an instrumentation amplifier suppresses signals that appear the same on both inputs. If CMRR is high, the output reflects mainly the difference between the inputs, with little influence from anything that both inputs see equally (like power-line hum, EMI, or ground noise). When CMRR is poor, part of that common-mode voltage leaks into the output as if it were part of the signal, so the amplifier shows more noise and error in the differential measurement. In other words, common-mode noise becomes differential at the output, reducing differential accuracy. The other statements don’t capture this effect: CMRR isn’t a direct measure of open-loop gain or bandwidth changes, and there is a practical consequence in real circuits when common-mode leakage occurs.