IP3 & Intermodulation Calculator
In a nonlinear RF system, two input tones at f₁ and f₂ generate intermodulation products at 2f₁−f₂ and 2f₂−f₁ (third-order IM, or IM3). These fall close to the desired signals and cannot be filtered out. The third-order intercept point (IP3) characterises linearity.
Equations & Parameters ▸
\(P_{IM3} = 3P_{in} - 2\cdot IIP3 + G\qquad OIP3 = IIP3 + G\qquad P_{1dB} \approx IIP3 - 9.6\,\text{dB}\)
| IIP3 | Input-referred 3rd-order intercept point (dBm). Higher is more linear. |
| Pin | Input power per tone (dBm). Two equal tones in a two-tone test. |
| Gain | Amplifier/system gain (dB). |
| OIP3 | Output IP3 = IIP3 + Gain. |
| IM3 | Output IM3 product power = 3·Pin − 2·IIP3 + Gain = 3·Pin_out − 2·OIP3. |
| IMD | Intermodulation distortion = difference between desired output and IM3 = 2·(IIP3 − Pin). |
Physical constants used
| c | Speed of light = 2.998×10⁸ m/s |
| µ₀ | Permeability of free space = 4π×10⁻⁷ H/m ≈ 1.2566×10⁻⁶ H/m |
| ε₀ | Permittivity of free space = 8.854×10⁻¹² F/m |
Inputs
dBm
higher = more lineardBm
equal two-tone testdB
amplifier gain or chain gainResults
Output Powers
Output signal power—
Output IP3 (OIP3)—
IM3 product power—
IMD ratio—
Margin
Headroom to IIP3—
Headroom to OIP3—
1-dB compression (P_1dB)—
Diagram