Sub-THz Power Amplifiers: Measurements, Behavioral Modeling and Predistortion Algorithms

TL;DR

This paper characterizes a 300 GHz power amplifier, develops behavioral models for its nonlinearities, and proposes a predistortion algorithm to mitigate distortions, enhancing THz transceiver performance for high-data-rate communications.

Contribution

It provides the first comprehensive measurement and modeling of a 300 GHz PA's nonlinearities and introduces a predistortion method tailored for THz PAs.

Findings

Models accurately capture AM-AM and AM-PM behavior across 270-330 GHz.

Predistortion significantly reduces error performance degradation.

Proper parameter selection improves multi-carrier waveform performance.

Abstract

With global IMT traffic expected to grow 10-100 times from 2020 to 20301, the Terahertz (THz) spectrum offers a promising solution to satisfy such forecasts. However, occupying the THz spectrum comes with its own challenges, an important one being impairments caused by broadband RF components in THz transceivers. Nonlinearities in power amplifiers (PAs) complicate meeting link budget requirements, with amplitude and phase distortions degrading the system's performance, especially when adopting waveforms with high peak-to-average power ratios (PAPRs), such as Orthogonal Frequency Division Multiplexing (OFDM). In this paper, we present characterization results of a 300 GHz PA using small-signal and large-signal continuous-wave measurements. Models capturing Amplitude-to- Amplitude Modulation (AM-AM) and Amplitude-to-Phase Modulation (AMPM) behavior across 270-330 GHz are developed and verified with wideband measurements, confirming the compression behavior, while nonetheless showing inaccuracies for low input powers due to unaccounted frequency dependencies. Based on the derived models, a predistortion algorithm is designed and analyzed, revealing significant error performance degradation when switching between single- and multi-carrier waveforms. We finally show that an appropriate selection of pre-distorter parameters can significantly improve the performance.