On IP2 impact to nonlinear distortion of RF amplifiers

Abstract

The second-order distortion, often using second-order intercept point (IP2) as an indicator, has been considered easy to be filtered in narrowband radio frequency (RF) communications because it is located far away from the passband of transmitted signals. However, with rapidly increased applications in wideband RF communications, the secondorder intermodulation (IM) might become important, partially evidenced by the increased appearances of IP2 in the amplifier datasheets in recent years. In this article, a power spectrum model of the second-order IM is derived to quantify the second-order distortion using the IP2. This model could be used to determine under what conditions, in terms of the relation between the carrier frequency and bandwidth, the second-order IM will affect the passband or the adjacent bands or other applications, using three types of frequency scenarios. These discussions are beneficial for RF engineers and spectrum planners to predict interferences from second-order IM. The experimental measurement at the end of the article validates the spectrum model. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Fourth‐order nonlinear distortion to the power spectrum of RF amplifiers

“…where P 0 = a 2 1 N 0 B∕2 is the power of the linear output. An interesting observation can be made from Equatiom (20), the frequency spread of the fourth-order IM around second harmonic 2 f c is twice as wide as that of the second-order IM at 2 f c [9]. This is because the Fourier transform of the fourth power to the autocorrelation F {R 4 s (𝜏)} in Equation ( 15) can be further decomposed as a four-time convolution of…”

“…We derived a power spectrum model of the second-order IM distortion in our previous work [9]. Inspired by the recent attention regarding higher even-order IM distortions, we are now focusing on fourth-order IM distortion and its impact to the passband and adjacent bands.…”

“…where ỹ4 (t ) Δ = a 4 s4 (t )∕2. Denoting the power spectrum of ỹ4 (t ) as P ỹ4 ( f ), the power spectrum P y 4 ( f ) of y 4 (t ) can be expressed as [9,11],…”