X-parameter Model Research Articles

Application of Load-Pull X-Parameters for GaN Device-Based Load Modulated Balanced Power Amplifier Design

In this work, the design of a load modulated balanced power amplifier (LMBA), which composed of a pair of classical balanced power amplifier (BA) and a signal control power amplifier (CA), based on using the X-parameter model is presented for the first time. A 10-W gallium nitride (GaN) packaged transistor is used for the power amplifier (PA) design. The extracted X-parameter model of the device under test (DUT) can accurately predict the nonlinear behavioral of the device, including both fundamental and harmonic characteristics, and determine the region of the Smith chart that leads to the optimal output power and drain efficiency (DE), with which the BA and CA are designed. In order to facilitate the application of the X-parameter for LMBA design, the X-parameter model of the classical BA pair is further extracted. Finally, an LMBA is fabricated and tested to verify the validity of the proposed design methodology. The measurements performed on the developed prototype show a saturation output power of up to 43.2 dBm in the frequency range of 1.3 GHz-1.6 GHz, with a saturation DE over 73% and an output power back-off (OBO) efficiency over 51% when it has more than 9 dB output power back-off. A single-carrier 20-MHz long-term evolution (LTE) signal is used to test the designed PA, and performance of the amplifier both with and without linearization are given.

Analysis of Trapping Effect on Large-Signal Characteristics of GaN HEMTs Using X-Parameters and UV Illumination.

GaN high-electron-mobility transistors (HEMTs) have attracted widespread attention for high-power microwave applications, owing to their superior properties. However, the charge trapping effect has limitations to its performance. To study the trapping effect on the device large-signal behavior, AlGaN/GaN HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) were characterized through X-parameter measurements under ultraviolet (UV) illumination. For HEMTs without passivation, the magnitude of the large-signal output wave (X21FB) and small-signal forward gain (X2111S) at fundamental frequency increased, whereas the large-signal second harmonic output wave (X22FB) decreased when the device was exposed to UV light, resulting from the photoconductive effect and suppression of buffer-related trapping. For MIS-HEMTs with SiN passivation, much higher X21FB and X2111S have been obtained compared with HEMTs. It suggests that better RF power performance can be achieved by removing the surface state. Moreover, the X-parameters of the MIS-HEMT are less dependent on UV light, since the light-induced performance enhancement is offset by excess traps in the SiN layer excited by UV light. The radio frequency (RF) power parameters and signal waveforms were further obtained based on the X-parameter model. The variation of RF current gain and distortion with light was consistent with the measurement results of X-parameters. Therefore, the trap number in the AlGaN surface, GaN buffer, and SiN layer must be minimized for a good large-signal performance of AlGaN/GaN transistors.

Design and Implementation of a Wideband, Highly-Efficient, High-Power Amplifier Using Load-Pull and X-Parameters Models

This brief presents the design process, fabrication, and measurement results of a 1-3 GHz, efficient, 90-watt power amplifier (PA). Our design method is based on the source-pull/load-pull and the X-parameter models of the transistor which were obtained using its nonlinear compact model. According to the measurement results, the fabricated PA provides an output power between 49 dBm - 50 dBm, a drain efficiency of 41.4% to 45.5%, and a power gain between 9.4 dB and 13.7 dB in the entire frequency band of 1-3 GHz.

X‐parameter modelling of GaN HEMT based on neural network

Currently, S-parameters are commonly used in the design, measurement, and modelling of microwave circuits, but it is only suitable for linear small-signal conditions and not suitable for large-signal conditions. X-parameter is more accurate than the S-parameter in characterising the non-linearity of the device or the microwave circuit, and the artificial neural network has significant advantages in predicting the non-linearity of the system. Based on theoretical analysis, this article selects the GaN HEMT device CGH40010F for X-parameter modelling. Using X-parameter generator of ADS software, the X-parameters of the device were obtained. An X-parameter model based on BP neural network was built using MATLAB neural network box. The accuracy of the model was verified by comparing the test data with the model prediction data.

A Study on Quadratic PHD Models for Large Signal Applications

Measurement-based black box behavioral models are widely used nowadays. To handle nonlinear effects efficiently, such models often rely on approximation techniques. Polyharmonic distortion (PHD) modeling emerged as a viable approach for describing a nonlinear mapping. Typical PHD-based models, such as the well-known X-parameter model, are gained from linearization while operating on a certain large signal (LS) operational point. This limits the accuracy, especially for hard nonlinearities. However, quadratic terms can be added, which result in the quadratic PHD (QPHD) model. This enables highly accurate models for devices in strongly nonlinear operation, even in highly mismatched environments. In this paper, the accuracy of such models is investigated by predicting typical nonlinear measures, such as load-pull contours and intermodulation distortion, to assess the model accuracy for both static and dynamic stimulus. Furthermore, the LS matching problem is solved for both the X-parameter and the QPHD model. This allows to predict the optimum matching analytically, without performing load-pull analysis. To verify the accuracy of the model, the results are presented by comparing the model prediction with verification measurements for a commercially available GaN HEMT.

The sublimative torques of Jupiter Family Comets and mass wasting events on their nuclei

Sublimative outgassing of comets produces torques that alter the rotation state of their nuclei. Recently, parameterized sublimative torque models have been developed to study rotation state changes of individual comet nuclei and populations of cometary bodies. However, these models simplify the interactions between the escaping gas and cometary surface into only a few parameters that hide the details of these complex interactions. Here we directly compare the X-parameter model (Samarasinha and Mueller, 2013) with the SYORP model (Steckloff and Jacobson, 2016) to tease out insights into the details of the gas-surface interactions driving sublimative torques. We find that, for both of these models to accurately model sublimative torques, the number of sublimating molecules that contribute to the net torque is largely independent of the detailed shape and activity of the nucleus, but rather depends primarily on the size of the nucleus and the effective heliocentric distance of the comet. We suggest that cometary activity must be largely restricted to regions of steep gravitational surface slopes (above the angle of repose), where mass wasting can refresh activity by shedding mantles of refractory materials and exposing fresh volatiles. We propose a new classification scheme for comets based on the frequency of this mass-wasting process (relative to the timescale of activity fading): quasi-equilibrium, episodic, quasi-dormant, and extinct.

X-Parameter Characterization of TC SAW Filters With Enhanced Dynamic Range

Increasing the integration of radio frequency frontend modules for mobile communication devices results in rising power densities within the components. Additionally, advanced communication techniques demand for more frequency bands to be supported. As a result, the probability of significant nonlinear emissions disturbing adjacent channels increases, and accurate modeling of the device’s response is required. The X-parameter-based modeling approach can be applied to this problem. In this paper, a measurement setup, which is based on a nonlinear vector network analyzer, is utilized in order to characterize a surface acoustic wave (SAW) filter. Due to the low power levels of the generated higher order harmonics and the demand for a power sweep, a high dynamic range (DR) is required. The application of frequency selective attenuators enables an increase of the effective DR by more than 40 dB. Based on this improved measurement setup, single-tone and two-tone X-parameter models of the SAW filter are created and evaluated for their ability to predict intermodulation distortion (IMD). Classic, scalar IMD measurements are used as a reference for the assessment of capabilities and limitations of both X-parameter approaches.

Gate Length Dependence of Large-Signal Output Characteristics for the MOSFETs in the Breakdown Region Using X-Parameter Model

In this letter, the gate length dependence of $\text{X}^{S}_{2121}$ and $\text{X}^{T}_{2121}$ intercept behaviors for the MOSFETs in the breakdown region is first analyzed using the X-parameter model. Shorter gate length decreases $\text{X}^{S}_{2121}$ coefficients and increases $\text{X}^{T}_{2121}$ coefficients at high drain voltage and high input power due to the significant RF avalanche effect in the high field region. $\text{X}^{S}_{2121}$ and $\text{X}^{T}_{2121}$ coefficients are determined using artificial neural network. Good agreement between the measured and fitted output scattering wave is achieved. The presented analysis for the gate length dependence $\text{X}^{S}_{2121}$ and $\text{X}^{T}_{2121}$ can be beneficial to CMOS power amplifier designs with the scaled-down MOSFETs.

Nonlinear Behavioral Modeling Dependent on Load Reflection Coefficient Magnitude

A new frequency-domain nonlinear behavioral modeling technique is presented and validated in this paper. This technique extends existing Padé and poly-harmonic distortion models by including the load reflection magnitude, |Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> |, as a parameter. Although a rigorous approach requires a full 2-D load-pull model to cover the entire Smith chart, simulation and experimental evidence have shown that such a 1-D model-that retains only amplitude information of the load reflection coefficient-can give accuracy close to that of a full 2-D load-pull model. Consequently, neglecting the phase constitutes an approximation that provides large benefits without appearing to lead to a severe compromise in accuracy. Furthermore, compared with traditional load-independent models, the new |Γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> |-dependent models provide a major improvement in model accuracy. After a discussion of the model extraction methodology, examples are provided comparing traditional load-pull X-parameter models with the model presented in this paper. The new model not only provides consistently good accuracy, but also has a much smaller model file size. Along with the examples that display the ability of the new modeling technique to predict fundamental frequency behavioral, a second harmonic example is also provided. The modeling approach is also validated using measurements results.

An improved quadratic poly-harmonic distortion behavioral model

In this paper, the basic quadratic form of the poly-harmonic distortion model is first presented and this is then extended to provide a new, modified quadratic poly-harmonic distortion model. Comparisons between the X-parameter model, the basic quadratic poly-harmonic distortion model, and the modified version are provided. Both simulation and experimental test results show that the new modified model provides significant improvements in accuracy, not only for the fundamental frequency, but also for DC. Work on the optimization of the model is also presented, providing further improvements in both the model extraction time and the file size.

Padé-Approximation-Based Behavioral Modeling

A new, nonlinear, frequency-domain behavioral model, based on Pade approximation theory, is presented in this paper. The new Pade model is similar in concept to the X-parameter method, but it uses a rational function instead of the X-parameter model's polynomial expression. The basic theory of the proposed Pade model and the model extraction methodology are provided. The proposed Pade approach increases the available modeling space beyond that available to the X-parameter method, and the performance of a selection of this family of models under various loading conditions is described in this paper. Along with the examples displaying the ability of the new model to predict fundamental frequency behavior, a second-harmonic example is also provided, with simulation results presented in both the frequency domain and the time domain. Based on the simulation studies and experimentally measured results, the new Pade model shows good accuracy and a high level of stability. All of these characteristics show that the proposed Pade model has high potential in RF design.

Modeling and Simulation of a Reflective Semiconductor Optical Amplifier Modulator Using X-Parameters

We present a behavioral model in frequency domain for a bulk reflective semiconductor optical amplifier (RSOA) used as a modulator in radio-over-fiber systems using X-parameters. X-parameters were extracted by the simulation based on the physical model of the RSOA in Agilent advanced design systems software. Unlike S-parameters, X-parameters consider magnitude and phase information on all harmonic and inter-modulation spectra. An excellent match was achieved between the results of the simulations based on the X-parameter model and the physical model. The X-parameters model based simulation, however, ran five times faster than the physical model based one. X-parameter models also allow intellectual property control.

Application of an NVNA-Based System and Load-Independent $X$-Parameters in Analytical Circuit Design Assisted by an Experimental Search Algorithm

Recently, X -parameters have been introduced to model active device nonlinear behavior. In addition to providing a measurement-based tool to numerically predict nonlinear device behavior in computer-aided design, they can also provide the designer of nonlinear circuits an analytical design tool. Exploiting this design tool aspect, this work presents an application that combines the nonlinear vector network analyzer PNA-X and a passive tuner to extract a transistor load-independent X -parameter model, focused around targeted circuit impedances for optimal performance. Furthermore, an experimental search algorithm, based on X-parameters analytical computations and developed by Pelaez-Perez , has been used and experimentally validated in this paper, aimed to speed up the characterization and design process, minimizing the number of load-pull measurements necessary to provide an accurate transistor X-parameter model for use in analytical and/or numerical circuit design.

Focus on software

The descriptions of the new products listed in this section are based on information supplied to us by the manufacturers. PHYSICS TODAY can assume no responsibility for their accuracy. For more information about a particular product, vis the website at the end of the product description.