A critical design goal for wireless is more efficient or greener devices, whether it’s reducing power consumption in base stations or boosting battery life across several billion handsets. Using active devices in their nonlinear region improves operating efficiency of wireless products.
Traditionally, characterizing nonlinear device behavior has involved the use of measurements and modeling to achieve optimum results. For measurements, Large-Signal Network Analyzers (LSNA) and Non-linear Vector Network Analyzers (NVNA) have attempted to address this market with application software and systems to assist with the behavioral measurements. However, these power amplifier (PA) measurement techniques lack a coherent and unifying link between development stages, adding significant system complexity to non-linear device characterization.
An emerging approach supports simultaneous measurement of actual current and voltage waveforms at the device and engineering of waveform shapes to boost efficiency. Designing a highly efficient PA is coupled to the precise control of the fundamental and harmonic impedances that are presented to the device. It is therefore critical that the designer be able to measure what is needed at relevant power levels and frequencies, with the signal complexity that is required for a given application.
In this article, we explore the evolution of non-linear measurement solutions and then detail an emerging approach that greatly reduces design iterations even for complex power amplifier modes while achieving performance closely matching theory. A variety of approaches to non-linear measurement have been attempted and each faces a number of challenges that have made it difficult to obtain maximum PA efficiency. These include passive source/load pull, closed loop active load pull and, more recently, open loop active load pull.