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Cascaded IIP3 & OIP3 Calculator: Find the Weak Link in Your Receive Chain

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Cascaded IP3 Calculator — GPIO Labs

RF system design tool — GPIO Labs

Cascaded IP3 calculator

Build a receive chain out of amplifiers and passive stages (cable, attenuators, filters) and see the cascaded input and output IP3 — plus which single stage is limiting your dynamic range.

How to use it: each card below is one stage, ordered from antenna (top) to receiver (bottom). Amplifier stages need gain and input IIP3; passive stages just need loss. Use the dashed insert links to add a stage anywhere in the chain, and the arrows to reorder.

Signal chain — antenna on the left, receiver on the right
System result
Cascaded input IIP3
— dBm
—
Total gain
— dB
sum across all stages
Limits dynamic range
—
—
Contribution to nonlinearity by stage
Two-tone interferer test

Enter the power of a nearby interfering signal as it arrives at your antenna (two equal-strength tones, closely spaced in frequency). This shows how strong the third-order intermodulation products your chain generates are, given the cascaded IIP3 above.

Preamp solver

Given the chain above as everything after a preamp, this solves for the minimum input IIP3 that preamp needs — at a gain you specify — to keep intermodulation products a chosen distance below the interferer.

Method

Cascaded input IIP3 is computed by converting each amplifier stage's gain and IIP3 to linear units and summing input-referred nonlinearity contributions:

1/IIP3_total = 1/IIP3₁ + G₁/IIP3₂ + G₁G₂/IIP3₃ + …

Passive stages (cable, attenuators) are treated as effectively linear — their IIP3 doesn't enter the sum — but their loss still reduces the accumulated gain ahead of later stages, exactly like negative-gain amplifier stages. Cascaded output OIP3 is simply input IIP3 plus total cascade gain. Third-order intermodulation suppression for a two-tone interferer is estimated as 2 × (IIP3 − Pin) dB below the interferer — a standard small-signal approximation. This tool is for system-budgeting purposes; it does not model compression (P1dB), higher-order products, or in-band filtering that may attenuate the interferer before it reaches later stages.