Electronics · Free Calculator
Instrumentation Amplifier Gain Resistor Calculator
Find the gain set resistor RG for popular instrumentation amplifier ICs, or the gain from a given RG.
AD620, AD8221INA128, INA333RG for gain3 op amp design
Gain resistor RG499 Ω
Nearest E96 (1 %)499 Ω
Gain with E96 value99.998
Gain error0.00 %
How this result was calculated
- RG = 49.4 kΩ ÷ (G − 1) = 49.4 kΩ ÷ 99 = 499 Ω
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Gain Equations
AD620, AD8221, INA129, INA826: G = 1 + 49.4 kΩ ÷ RG
INA128: G = 1 + 50 kΩ ÷ RG
INA333: G = 1 + 100 kΩ ÷ RG
Discrete 3 op amp: G = 1 + 2R ÷ RG (difference stage at unity gain)
INA128: G = 1 + 50 kΩ ÷ RG
INA333: G = 1 + 100 kΩ ÷ RG
Discrete 3 op amp: G = 1 + 2R ÷ RG (difference stage at unity gain)
Worked example
An AD620 needs a gain of 100: RG = 49.4 kΩ ÷ 99 = 499 Ω, exactly an E96 value.
Key insight: the gain error of an in amp comes mostly from RG, so use a 0.1 % or 1 % low drift resistor and keep its leads short; any trace resistance in series adds directly to RG at high gain.
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Frequently Asked Questions
How do I set the gain of an AD620?
Fit RG = 49.4 kΩ ÷ (G − 1) between the RG pins. For G = 10, RG = 5.49 kΩ.
What gain does an instrumentation amplifier have with no RG?
Unity (G = 1) for most ICs.
Why use an instrumentation amplifier for a bridge?
It has very high, balanced input impedance and high CMRR, so it reads the small differential signal without loading the bridge.
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