RF and Antennas
Model class: Standard approximation
Cascaded IP3 and compression planner
Combine two cascaded stages' third-order intercept points into an input-referred cascaded IIP3.
Interactive engine
Start with the stated conditions.
Values stay in this browser. Choose a representative scenario, then calculate deliberately.
Example ready
Calculate to inspect the result.
The result will identify the direct answer, assumptions, and any warning that changes the next decision.
Assumptions to check
- The entered cascaded-linearity values represent the stated operating condition.
- This standard approximation is evaluated in the declared lumped or first-pass model.
- A cascaded-linearity calculation is not a component qualification or safety approval.
What this cascaded-linearity calculation establishes
Combine two cascaded stages' third-order intercept points into an input-referred cascaded IIP3. The useful result is the stated electrical quantity and the decision it supports, not an unstated claim about a finished product. This engine keeps the governing relationship visible so an input, unit, condition, or model boundary can be reviewed before a value becomes a component or layout choice.
Both stages' third-order intercept powers are referred to the input and combined by reciprocal-power addition, weighted by the first stage's linear gain. Treat the number as a first-pass result for the declared operating point. When a source, load, temperature, frequency, waveform, component tolerance, or measurement condition changes, repeat the calculation at the relevant corner rather than assuming the nominal answer persists.
Worked decision context
Two unity-gain stages each with IIP3 = 30 dBm combine to about 26.99 dBm IIP3 under reciprocal-power addition. That example verifies the equation and illustrates the scale of the result, but it does not select a part by itself. Compare the result with available values, ratings, tolerance bands, and the receiving circuit or physical environment before implementation.
Use the primary output to identify the binding constraint. If it leaves little margin, document which input dominates and use selected-part data, a higher-fidelity model, simulation, or measurement. This is especially important when a small numerical difference changes a thermal, timing, noise, or reliability decision.
Limits and validation handoff
P1dB compression should be checked separately and propagated with its own stage headroom, not derived from IP3 by a fixed offset. The calculation does not silently include omitted parasitics, installation conditions, manufacturing variation, or product policy. Those conditions can be decisive even when the arithmetic is exact for the selected model.
Record inputs, units, model assumptions, and the intended decision with the result. Verify the leading risk against the selected component data sheet and a representative measurement when the circuit has consequential energy, high voltage, safety, compliance, or reliability requirements.
Common mistakes
- Treating the cascaded-linearity result as a guaranteed operating limit rather than a first-pass standard approximation estimate.
- Mixing a data-sheet value measured under one condition with this cascaded-linearity calculation performed at another.
- Selecting a component before checking the boundary this calculation names: p1dB compression should be checked separately and propagated with its own stage headroom, not derived from IP3 by a fixed offset.
Model limit and handoff
Keep the entered cascaded-linearity conditions with the calculation, then validate the binding limit using the selected component, physical implementation, and representative operating corner.
FAQs
Is this cascaded-linearity result sufficient to approve a design?
No. It applies standard approximation reasoning to the entered cascaded-linearity values and names the checks that still need selected-part data, a higher-fidelity model, or measurement. P1dB compression should be checked separately and propagated with its own stage headroom, not derived from IP3 by a fixed offset.
What does this cascaded-linearity calculator assume that could make the result wrong?
Both stages' third-order intercept powers are referred to the input and combined by reciprocal-power addition, weighted by the first stage's linear gain. If the entered values do not match the real operating condition, the result no longer describes the actual circuit.
Where should this cascaded-linearity result go next?
Compare this cascaded-linearity result with RF link budgets and real-world margin, then use the stated next decision below the calculator to move from this first-pass number toward an implementation.