In 1996, he joined a nonprofit governmental organization, Small Business Corporation, Shiheung, Korea. He was a Product Development Assistant Consultant until 2007, and had been involved in over 100

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n the last decades, vector network analyzers (VNA) have been successful for the characterization and modeling of time-invariant RF devices exhibiting mildly nonlinear response using swept continuous wave (CW) excitations. As the demand on wireless communication has grown, new modulation schemes such as WiMAX and long-term evolution (LTE) have been introduced that require higher peak-to-average-power ratio (PAPR) in the time-domain and wider bandwidth in the frequency domain. These modulated signals have forced many components, especially power amplifiers, to operate in a harsher nonlinear regime. Modern power amplifiers must therefore handle modulated signals with higher PAPR while keeping high average power. To assist with the device modeling and the amplifier design process, improved measurement systems are required which characterize their nonlinear response under realistic operating conditions.Since the first work reported by Lott in 1989 [2], many large-signal VNAs (LSNAs) or nonlinear VNAs (NVNAs) have been developed to characterize, under calibrated conditions, nonlinear devices excited by CW or periodically modulated RF signals. The LSNA and NVNA measure the absolute amplitude and relative phase of the harmonics of voltage and current waves at the measurement reference planes. Among the various architectures, the most popular are the sampler-based LSNAs and the mixer-based NVNAs. The

-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.

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