IIP3 Calculator and Formula: Calculate Input Intercept Point

This article explains how to calculate IIP3 (Input Intercept Point 3) using the IIP3 formula, based on gain and OIP3 (Output Intercept Point 3) values. We’ll also cover OIP3 calculation using fundamental frequencies and third-order intermodulation product powers.

Understanding OIP3 Calculation

When two or more signals are fed into nonlinear RF components like amplifiers or mixers, they generate undesired signals in addition to the intended ones. These unwanted signals include harmonics, spurious signals, and intermodulation products (IMD) of the fundamental input signals. Among these, third-order intermodulation products (IMD3), located at 2F1-F2 and 2F2-F1, are a major source of interference.

Here’s a visual representation of an IM3 measurement setup:

IP3 measurement setup for IIP3 and OIP3

In the diagram above:

• Wa and Wb represent the fundamental frequencies.
• 2*Wa - Wb and 2*Wb - Wa represent the IMD products.

Pout designates the power of the fundamental frequencies, and Pout_3 designates the power of the third-order products. ΔP is calculated as the difference between Pout and Pout_3. These values are used in both the OIP3 and IIP3 calculators. Refer to more detailed resources for a deeper understanding of IIP3 and OIP3 basics.

OIP3 Calculator

The calculator determines OIP3 using the power of the fundamental signals (Pout) and the power level difference (ΔP) between the fundamental and IMD products (Pout_3).

Example:

• Input: Pout in dBm = -10, ΔP = +30dBc
• Output: OIP3 in dBm = +5 dBm

Important Note:

If IM3 products (2f1-f2 and 2f2-f1) are measured at a power level of -40dBm and fundamental signal frequencies (f1, f2) are at -10 dBm, then ΔP can be calculated as -10 dBm - (-40dBm) = +30 dBc.

IIP3 Formula & Calculation

OIP3 as a Foundation for IIP3

Before calculating IIP3, OIP3 is typically determined using the powers of the fundamental and IMD signals. It is assumed that the power levels of the signals at f1 and f2 are equal. The power levels of the signals at the IMD products (2F1-F2 and 2F2-F1) are also assumed to be equal.

The IIP3 Formula

The following formula is used for IIP3 calculation:

IIP3 formula

IIP3 Calculator

The IIP3 calculator determines IIP3 based on the OIP3 and the gain of the device.

IIP3 Calculator: (Provide Calculator Here - Needs HTML/JS implementation)

Example:

• Input: OIP3 = 5 dBm, Gain = 7 dB
• Output: IIP3 = -2 dBm