Nonlinearity Basics and Types

This page covers nonlinearity basics and mentions types of nonlinearity: power nonlinearity, frequency nonlinearity, and phase nonlinearity.

What is Nonlinearity?

Fig.1 Nonlinearity basics

If a system is nonlinear, it will generate frequencies outside of the intended frequency band, thus causing interference to other nearby signals used by users. For a memory-less, nonlinear system, the output and input will follow an exponential curve, rather than following a linear straight-line relationship.

The relationship can be represented as:

$Y(t) = A_1 x(t) + A_2 x^2(t) + A_3 x^3(t)$

Nonlinearity Types

Power Nonlinearity

This is caused by amplitude distortion in the device. It’s typically measured by the 1dB gain compression point.

Frequency Nonlinearity

This arises due to frequency/phase-related distortion. It’s measured using two-tone tests, specifically using the TOI (Third Order Intercept Point).

Phase Nonlinearity

This is caused by amplitude distortion due to phase variation. It’s measured by AM-to-PM conversion.

For example:

• An RF Mixer device is nonlinear in the frequency domain but not in the power domain.
• An RF amplifier is nonlinear in the power domain but not in the frequency domain.