Instrumentation Amplifier Calculator

An instrumentation amplifier is a type of differential amplifier that provides high input impedance, low noise, and adjustable gain. It's commonly used in measurement and sensor applications where small differential signals need to be amplified while rejecting common-mode noise.

The circuit uses two op-amps in the first stage to provide high input impedance and variable gain, followed by a third op-amp configured as a difference amplifier. The gain is primarily set by the Rgain resistor connecting the two input op-amps.

The total gain is the product of first stage gain and second stage gain. First stage gain = 1 + (2×R1)/Rgain, and second stage gain = R3/R4 (assuming R2=R3 and R1=R4 for the difference amplifier stage).

Rgain determines the gain of the first stage. A smaller Rgain value provides higher gain. Use the formula: Rgain = (2×R1)/(Gain - 1), where Gain is the desired first stage gain and R1 is the input stage resistor value.

Key advantages include very high input impedance, excellent common-mode rejection ratio (CMRR), low offset drift, and easy gain adjustment with a single external resistor (Rgain).

Common applications include strain gauge amplifiers, thermocouple amplifiers, medical instrumentation (ECG, EEG), data acquisition systems, and any application requiring precision amplification of small differential signals.

To maximize CMRR, ensure resistor matching in the output stage (R2=R3 and R1=R4), use precision resistors with low tolerance, and select op-amps with inherently high CMRR specifications.

Choose R1 and R4 values between 1kΩ to 100kΩ for good noise performance. Ensure R2=R3 and R1=R4 for optimal CMRR. Select Rgain based on desired gain, keeping in mind that very small values may introduce noise.