Cascade Gain + IP3 (Linearity) Calculator

Enter per-stage gain (dB) and input-referred IP3 (IIP3, dBm). The calculator finds the overall cascade IIP3 and OIP3 using the standard third-order intermodulation formula.

Stages (leave unused rows blank)

Stage	Gain (dB)	Input IP3, IIP3 (dBm)
1
2
3
4
5
6

Result will appear here.

Total gain

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Overall IIP3

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Overall OIP3

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1/IIP3 sum check

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Uses input-referred IP3 (IIP3). To compute overall IIP3, this tool applies: 1/IIP3_tot = 1/IIP3₁ + G₁/IIP3₂ + G₁G₂/IIP3₃ + …, with all gains and IP3 values in linear power units.

Per-Stage Contribution & Theory

Relative contribution of each stage to 1/IIP3_total:

Stage	Gain (dB)	IIP3 (dBm)	Term in 1/IIP3_tot	Contribution (%)

Key formulas:

G (linear) = 10^( G_dB / 10 )

P_W = 10^((P_dBm − 30)/10)

1/IIP3_tot = 1/IIP3₁ + G₁/IIP3₂ + G₁G₂/IIP3₃ + …

This expression is in linear power units (e.g., Watts). After computing IIP3_tot in Watts, it is converted back to dBm. The overall OIP3 is simply OIP3_tot = IIP3_tot + G_total (in dB scale).

Physical interpretation:

The first stages dominate overall linearity, especially if they have high gain and limited IP3.
A very linear but low-gain first stage can be “spoiled” by a high-gain, low-IP3 stage later in the chain.
Attenuators (negative gain) placed before non-linear devices can improve overall IIP3 but reduce sensitivity.