Which characteristic is a healthiness feature of instrumentation amplifiers when interfacing sensors?

• A. High input impedance
• B. Low CMRR
• C. High output impedance
• D. High input bias currents

Answer: (A)

High input impedance is the key trait that keeps the sensor signal healthy when you connect it to an instrumentation amplifier. By presenting a very high impedance, the amplifier draws almost no current from the sensor, so the sensor’s voltage is not loaded or altered by the input stage. This prevents voltage divider effects with the sensor’s source impedance, preserves signal amplitude and bandwidth, and minimizes measurement error for high-impedance or high-impedance sources.

If the input impedance were low, the sensor would be loaded, changing the reading and potentially distorting the signal. Conversely, a high common-mode rejection ratio is desirable, but it relates to rejecting unwanted common-mode signals rather than loading, while high output impedance or high input bias currents would hinder signal integrity by making the load larger or drawing more current from the sensor.