Core purpose of an instrumentation amplifier: Is it designed to extract and amplify very small differential signals while rejecting large common-mode voltages present on both inputs?

Introduction / Context:
Instrumentation amplifiers (INAs) are precision differential amplifiers optimized for accurate, low-noise amplification of tiny signals in the presence of large common-mode voltages. They are widely used in sensor interfaces such as strain gauges, thermocouples, and biopotential measurements where signal integrity and common-mode rejection are critical.

Given Data / Assumptions:

• Differential input signal is small (microvolts to millivolts).
• Common-mode voltage can be large relative to the signal of interest.
• High input impedance and precise gain setting are desirable.
• Common-mode rejection ratio (CMRR) must be high over frequency and temperature.

Concept / Approach:
An INA presents very high input impedance, provides a well-defined and easily adjustable gain (often with a single external resistor), and offers excellent CMRR. Its architecture—commonly a three-op-amp topology—separates input buffering from differencing, enabling accurate gain without loading the source and robust rejection of common-mode error sources such as ground offsets and interference.

Step-by-Step Solution:

Verification / Alternative check:
Compare with a single op-amp differential amplifier. The INA’s buffered inputs minimize source loading and resistor mismatch errors that would otherwise degrade CMRR and accuracy in the simpler circuit.

Why Other Options Are Wrong:

Common Pitfalls:
Mismatched input filtering that spoils CMRR, poor grounding, and routing sensitive inputs near noisy traces—all reduce the practical benefits of an INA.

Final Answer:
Correct