Simulation and measurement-based X-parameter models for power amplifiers with envelope tracking

Abstract

-Static X-parameter (XP) models for RF power amplifiers (PAs), derived from both simulations and nonlinear vector network analyzer (NVNA) measurements, are investigated for the prediction of PA performance under dynamic signal conditions such as in envelope tracking (ET). The instantaneous AM-AM, AM-PM and PAE predictions of XP models extracted from simulation are compared under ET dynamic signal conditions to two types of circuit models using envelope simulation. An XP PA model is extracted for a peak 8W GaN class-F -1 ET PA from NVNA measurements with automated bias control. By applying a constant gain shaping table derived from the XP model to the drain supply voltage, the average PAE is improved from 40% to 57% for 3.84 MHz WCDMA signals at 2.14 GHz compared to fixed drain bias operation.

Extension of NVNA Baseband Measurement for PA Characterization Under Complex Modulation

“…kind have been widely used for X-parameter modeling and associated applications, which are mainly based on harmonic nonlinearity characterization [2]- [4].…”

Modeling envelope-tracking RF amplifiers

“…Various modeling techniques have been reported in the past decades [5][6][7]. Even if many of them offer good accuracy, it's difficult to envision them to model ET PAs and difficult to use their characteristics/kernels to invert the memory influence.…”

Applications of X-parameters in behavioral modeling of RF power amplifiers for wireless communications: An overview

“…A couple of published work have put the effort on investigating and exploring the possibilities of X-parameter to model three-port PAs. In [8], a 8 W peak power GaN inverse class-F envelope-tracking PA is modeled only by static X-parameters where the envelope port of the PA under study is treated as a static DC port and frequency dependence on the envelope path is neglected. However, it validates that the static X-parameters are already good enough to characterize the behavior of the specific envelope-tracking PA in that work to meet commercial specifications.…”

“…The limitation of this quasi-static approach presented in [8] is explored further by considering the envelopetracking PA operating in a mixer-like mode in [9]. The DUT in this work is a 10 W GaAs envelope-tracking PA operating at 850 MHz.…”