Instrumentation Amplifier Calculator

Instrumentation Amplifier (3-op-amp) provides high input impedance and precise differential gain. Enter any 4 of the 5 design variables to solve the fifth.

• Gain: G = (1 + 2·R2/Rgain) · (R4/R3)
• Gain resistor: Rgain = 2·R2 / (G·R3/R4 − 1)

When you need it: Amplifying a small differential sensor signal — a bridge, thermocouple or current-shunt — while rejecting the common-mode noise riding on both inputs, all set by one gain resistor.

Worked example: An AD620-style in-amp sets gain by G = 1 + 49.4k / Rg; for a gain of 100, Rg = 49.4k / 99 ≈ 499 Ω. A 10 mV bridge output then becomes 1 V at the ADC.

Tips & gotchas:

• Common-mode rejection (CMRR) is the whole point for bridge and shunt sensing — check it at your gain and frequency.
• Drive the reference pin from a low-impedance mid-supply for single-supply operation, or CMRR collapses.
• Gain-resistor tolerance maps directly to gain error — use a precision part for accurate scaling.
• Provide a DC return path for the input bias currents (e.g. resistors to the reference) or the output drifts to a rail.