Troels Studsgaard Nielsen

Dynamic FET model - DynaFET - for GaN transistors from NVNA active source injection measurements

A complete nonlinear characterization and modeling flow for modern GaN transistors is presented. Features include a new active-source injection based waveform measurement HW/SW system built around an NVNA, an extended artificial neural network (ANN) training infrastructure for coupled electro-thermal and trap-dependent model constitutive relations, and the native implementation in a commercial simulator. The model is validated by detailed comparisons to measured data for an advanced mm-wave 150 nm 6×60μm GaN HFET manufactured by Raytheon Integrated Defense Systems. Excellent results are achieved for DC, S-parameters, harmonic and intermodulation distortion, and load-pull figures of merit, over a very wide range of bias conditions, complex loads, powers, and frequencies.

High-power, high-efficiency power amplifier reference design in III-V wide bandgap gallium nitride technology using nonlinear vector network analyzer and X-parameters

This paper presents a complete power amplifier design using new Nonlinear Vector Network Analyzer (NVNA) and X-parameter technologies. A high-power, pulsed Continuous Wave (CW) NVNA setup is presented and harmonic tuning capabilities of the measured X-parameter model is demonstrated using the same setup. From fundamental and harmonic impedance tuning, input and output power amplifier matching networks are synthesized and first-pass design success is confirmed by measurements of the fabricated power amplifier.

Doherty Power Amplifier Design in Gallium Nitride Technology Using a Nonlinear Vector Network Analyzer and X-Parameters

This paper presents a complete Doherty power amplifier design that has been developed entirely inside the circuit simulator, but using nonlinear vector network analyzer data and measured X-parameter models. A high-power nonlinear measurement setup with active load-pull capabilities is presented and used to extract X-parameters of a commercially available Gallium Nitride power transistor. From fundamental and harmonic impedance tuning of the measured X-parameter models, main and auxiliary amplifier matching networks are designed and proper splitter/combiner circuitry is developed to achieve optimum Doherty output power and power added efficiency. A first-pass design success (only one fabrication build is required to meet design specifications) is confirmed by measurements of the fabricated power amplifier.

Memory models for behavioral modeling and digital predistortion of envelope tracking power amplifiers

Abstract New advanced Envelope Tracking (ET) techniques can provide RF (Radio Frequency) transmitters with high-efficiency Power Amplifiers (PAs). On the other hand, system complexity substantially increases, requiring more advanced PA models for the representation and compensation of ET PA distortion effects. In this context, this paper proposes some solutions for behavioral modeling and digital predistortion of ET PAs. The adopted modeling strategy consists in including the modulated supply voltage as an additional independent model variable to define more accurate behavioral models capable of an increased accuracy when applied to model and compensate ET PAs. The new model variable is included in a polynomial model with memory whose nonlinear structure is derived from a binomial power series, whence the name of Memory Binomial Model (MBM). Another modeling approach is subsequently proposed, where the Cann model for static PA AM/AM nonlinearities is extended to model both AM/AM and AM/PM dynamic distortion occurring in ET PAs. The Extended Cann model includes an MBM structure for modeling dynamic AM/PM distortion effects. Both modeling approaches are tested on measured data-sets acquired using an ET measurement set-up including a commercial PA from RFMD and an envelope modulator designed using a commercial IC from Texas Instruments. The measured results showed that the proposed models could obtain a better modeling and predistortion performance when applied to ET PAs, with respect to the Memory Polynomial Model, here considered as a reference to represent the state-of-the-art of PA modeling and digital predistortion.

On wafer X-parameter based modeling of a switching cascode power amplifier

X-parameters have been introduced as the natural extension of S-parameters capable of characterizing a nonlinear device excited by a large-signal input. This paper describes validation of the X-parameter model of a switching cascode power amplifier (PA), which has strong nonlinearity. The X-parameter model of the PA was measured and extracted by an Agilent N5245A PNA-X. Measurements were done on wafer and deem-bedded to the input and output pads of the device. An Enhanced Data rates for GSM Evolution (EDGE) signal was applied to the model for simulations. The simulated relative levels of output spectrum and RMS value of error vector magnitude (EVM) were compared with the measured data in order to validate the X-parameter model. A good match was achieved between the simulation and measurement. The maximum difference between the simulated and measured relative levels of output spectrum is 4 dB. The maximum error between the simulated and measured EVM is less than 3 %-point.

Modeling power amplifiers with antenna mismatch

The paper presents an approach for behavioral level power amplifier modeling with antenna mismatch. The derived model is based on device large signal S-parameter measurements of a commercially available W-CDMA power amplifier. The measurement setup is described in detail and the model validity is verified by comparing measured and simulated adjacent channel power ratios (ACPR). The measured and simulated ACPR show very good agreement and match at the nominal drive level to within 2 dB over the maximum output VSWR ratings.

Digital predistortion method based on dynamic X-parameters

An original way is presented to predistort signals for microwave components that show modulation-induced baseband memory effects. The method is based on the recently introduced dynamic X-parameter modeling technique for power amplifiers.

Design and analysis of a verification device for the nonlinear vector network analyzer

We propose a verification device to validate the calibration of a nonlinear vector measurement instruments such as Nonlinear Vector Network Analyzer (NVNA). The verification device is a two-port device that has two operating modes, namely linear and nonlinear. The designed circuits response is almost insensitive to small harmonic mismatches of the instrument ports (|Γ| <; 0.1). Since neither an amplifier nor a circulator is used, the traceability procedure of the device to Electro-Optical Sampling (EOS) is less complicated compared to earlier prototypes.

Wideband limit study of a GaN power amplifier using two-tone measurements

This paper studies the wideband limit (WBL) of a GaN RF power amplifier (PA). The WBL study is achieved by a PA characterization using two-tone measurements. The characterization method allows to identify the dependency of PA memory effects on the two-tone frequency spacing. PA memory effects (MEs) are measured using the opening in the AM/AM and AM/PM curves and they were found to be located in a limited range of tone spacings. The outcome of this characterization procedure is the identification of the PA wideband limit defined as the upper limit of the MEs frequency range. The most interesting phenomenon related to the WBL is that for all tone spacings beyond the WBL the AM/AM curves of the PA collapse to a quasi-static case, which is different from the static case. The presence of the wideband limit is not so evident from AM/PM curves, where the phase loop is not collapsing beyond WBL. The wideband limit is an important aspect of the DUT behaviour and can be used to improve the accuracy of the DUT behavioral model identifying its memory range.

Fast predistorter adaptation to varying antenna load

The effect of varying power amplifier (PA) output VSWR is studied in a workfunction predistorter system. The resistive load of a commercially available W-CDMA PA is tuned and the large-signal S-parameters measured. From the measurements, the optimum gain and phase predistortion functions are derived and studied. The predistorter coefficients are parameterized with a single variable that roughly fits optimum predistortion functions for other than nominal PA loading conditions. The adaptation speed is evaluated in a complete predistorter system simulator and it is found that the number of iterations needed to adapt is reduced from 4 to 1.