What is a key limitation of instrumentation amplifiers in precision sensor applications?

• A. Infinite CMRR at all frequencies
• B. Noise and offset drift, especially at higher frequencies when CMRR falls
• C. Zero bias currents
• D. Perfect linearity

Answer: (B)

The core idea is how finite common-mode rejection and its frequency dependence limit precision in instrumentation amplifiers. These amplifiers are designed to amplify the difference between two inputs while suppressing anything that’s common to both. In an ideal world that suppression would be infinite, but in reality the common-mode rejection ratio (CMRR) is finite and decreases as frequency increases. That means at higher frequencies, some of the common-mode noise or drift picked up by the sensors can leak into the output as differential signal. The result is more noise and a shifting baseline (offset drift) as bandwidth grows or temperature changes, which is exactly what degrades precision in sensor measurements.

So the best answer highlights that noise and offset drift get worse at higher frequencies because CMRR falls off. In practice, the notions of infinite CMRR, zero bias currents, or perfect linearity aren’t achievable, which is why those options are not the best description of the limitation.