Nonlinearity basics and types

This page covers Nonlinearity basics and mention types of nonlinearity viz. power nonlinearity,frequency nonlinearity and phase nonlinearity.

What is Nonlinearity?

Nonlinearity basics Fig.1 Nonlinearity basics

If a system is non linear it will generate frequencies outside of intended frequency band and thus cause interference to other nearby signals used by users.

For a memory less, nonlinear system output and input will follow exponential curve, rather than following linear straight line relationship.
Y (t) = A1 x(t) + A2 x2(t) +A3 x3(t)

Nonlinearity types:

Power Nonlinearity: It is caused due to amplitude distortion in the device. It is measured by 1dB gain compression point.

Frequency nonlinearity: It is caused due to frequency/phase related distortion. It is measured by two tone tests i.e. using TOI Point (Third Order Intercept Point).

Phase Nonlinearity: It is caused due to amplitude distortion due to phase variation. It is measured by AM-to-PM conversion.

For example, RF Mixer device is nonlinear in frequency domain and not in power domain.

RF amplifier is nonlinear in power domain and not in frequency domain.

Useful Links

AM-PM conversion   P1dB vs TOI   second order intercept point vs third order intercept point  

RF and Wireless Terminologies