RFIP3 and OIP3 Calculator: Formulas and Explanation
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This article explains how to calculate IP3 (Third-Order Intercept Point) and OIP3 (Output Third-Order Intercept Point) using dedicated calculators and formulas. We’ll delve into the concepts of IM3 (Third-Order Intermodulation Distortion) and its relationship to IP3 and OIP3.
Understanding IP3 and IM3
When two signals (F1 and F2) are fed into a non-linear RF component or system, like a mixer or amplifier, it produces output signals not only at the original frequencies but also at intermodulation frequencies. These are products of the input fundamental signals.
The output consists of first-order, second-order, and third-order products. The most significant source of interference often stems from the third-order products, specifically 2F1-F2 and 2F2-F1. This is because they have higher amplitudes and are closer in frequency to the fundamental signals. These unwanted signals are called Intermodulation Distortion (IMD) products.
As depicted in the IMD curve (which has a slope of 3), let’s clarify the terms IM3_low, IM3_high, and OIP3. For more background, refer to the IIP3 and OIP3 basics.
The extrapolated point where the IM3 power level reaches 0 dBc is known as the Third-Order Intercept Point (IP3). In other words, it’s the point where the extrapolated curves of the fundamental signal and the third-order distortion product signal intersect.
At this intersection, the input power level is termed IIP3 (Input IP3), and the corresponding output power is termed OIP3.
Let’s now explore how to calculate IP3 and OIP3 using the calculators provided and the associated formulas.
IP3 Calculator
This calculator determines the IM3_low and IM3_high values based on the powers of the fundamental signals (P_low and P_high) and the OIP3 value.
Example:
- Input: P_low at F1 = 0 dBm, P_high at F2 = -12 dBm, OIP3 = 14 dBm
- Output: IM3 (low) = -40 dBm, IM3 (high) = -52 dBm
IP3 Formula
The following formula is used within the IP3 calculator:
OIP3 Calculator
The OIP3 calculator computes OIP3 values based on the powers of the fundamental signals (P_low and P_high) and the IM3 product values (IM3_low and IM3_high).
Example:
- Input: P_low = 0 dBm, P_high = -10 dBm, IM3_low = -40 dBm, IM3_high = -50 dBm
- Output: OIP3 = 15 dBm
OIP3 Formula
The following OIP3 formula is employed in the OIP3 calculator:
For further reading, you can also investigate IIP3 calculation and OIP3 calculation scenarios where the powers of the fundamental signals are equal, and the powers of the IMD products are equal, using an IIP3 calculator.
