Nonlinear Characterization and Modeling of Radio-Frequency Devices and Power Amplifiers with Memory Effects

Despite the fast development of telecommunications systems experienced during the last two decades, much progress is expected in the coming years with the introduction of new solutions capable of delivering fast data-rates and ubiquitous connectivity. However, this development can only happen through the evolution of radio-frequency systems, which should be capable of working at high-power and high-speed. At the same time, the power dissipation of these systems should be minimized. In this dissertation, methods for the characterization and modeling of transistors and power amplifiers are presented, along with the necessary nonlinear measurements techniques. In particular, dynamic electrical effects, originated by the properties of the semiconductor materials and by the system configurations, are investigated. Consequently, these phenomena, which cannot be ignored to obtain the wanted performance, are empirically identified and included in models for Gallium Nitride (GaN) transistors and power amplifiers driven by a dynamic voltage supply

Beam-Dependent Active Array Linearization by Global Feature-Based Machine Learning

An approach based on machine learning is proposed for the global linearization of microwave active beamforming arrays. The method allows for the low-complexity real-time update of the digital predistortion (DPD) coefficients by exploiting order-reduced model features, hence avoiding the need for repeated local DPD identification steps across the various operating conditions of the beamformer (e.g., different beam angles or RF power levels). The validation is performed by over-the-air (OTA) measurements of a 1×4 array operating at 28 GHz across 100-MHz modulation bandwidth (BW)

Automatic Extraction of Measurement-Based Large-Signal FET Models by Nonlinear Function Sampling.

A new method is proposed for the accurate experimental characterization and fully automated extraction of compact nonlinear models for Field-Effect Transistors (FETs). The approach, which leads to a charge-conservative description, is based on a single large-signal measurement under a two-tone sinusoidal wave excitation. A suitable choice of tone frequencies, amplitudes, and bias allows to adequately characterize the transistor over the whole safe operating region. The voltage controlled nonlinear functions describing the two-port FET model can be computed over an arbitrarily dense voltage domain by solving an overdetermined system of linear equations. These equations are expressed in terms of a new Nonlinear Function Sampling operator based on a bi-periodic Fourier series description of the acquired frequency spectra. The experimental validation is carried out on a 0.25-μm Gallium Nitride (GaN) on Silicon Carbide (SiC) High-Electron Mobility Transistor (HEMT) under continuous-wave (CW) and two-tone excitation (intermodulation distortion test).This project was partially supported by the Spanish Ministerio de Ciencia, Innovación y Universidades in the frame of ‘Salvador de Madariaga’ Program PRX18/00108

Measurement-based FET analytical modeling using the nonlinear function sampling approach

A novel and fast method for the measurement-based identification of an analytical FET compact model from large- signal waveforms is presented. Based on a two-tone two-port experiment, a recently published Nonlinear Function Sampling (NFS) operator providing the samples of the FET state functions in the voltage domain is here exploited, for the first time, to extract an equivalent-circuit model. The approach is demonstrated on a 250-nm GaN-on-SiC HEMT at 2.5 and 5 GHz

TC-2 Design Automation Committee—On the Future of RF and Microwave Design Automation—2022

TC-2 Design Automation Committee (formerly MTT-1 CAD), established in 1968, focuses on advances in all aspects of methods, software, and technologies for the modeling, simulation, and design optimization of high-frequency circuits and systems. From radio frequency to terahertz, engineering innovation hinges on the availability of state-of-the-art modeling techniques and design automation methods capable to handle new mathematical representations and design methodologies, as well as novel manufacturing processes and materials. Here, we venture on the future of RF and microwave design automation within the next decade.ITESO, A.C

Nonlinear Characterization and Modeling of Radio-frequency Devices and Power Amplifiers with Memory Effects

To reach demanding linearity and efficiency specifications, radio-frequency (RF) power amplifier (PA) design is evolving from the classical linear or quasi-linear topology into complex architectures. In such conditions, various mechanisms of distortion arise, which are dependent both on the PA topology as well as on the semiconductor technology upon which the PA is designed. This work makes use of tailored large-signal measurement techniques in order to characterize and model such distortions in modern applications. In particular, two distinct fields of applications are investigated. The first one deals with the characterization and modeling of the non-idealities shown by Gallium Nitride (GaN) HEMTs. In particular, the effect of charge trapping is characterized with the exploitation of a double-pulse technique, capable of preconditioning the charge trapping state. Such a method has been used in a new GaN HEMT modeling approach. The second part deals with supply-modulated RF PAs, in architectures such as envelope-tracking (ET). In this work, measurement techniques aimed at the characterization of the interface between the PA and the supply modulator at the drain-supply terminal have been introduced. Then, a three-port behavioral model, taking into account the presence of a modulated supply voltage and the mutual dynamic interaction with the modulated RF input, is proposed. Such a model, based on a modified Volterra series truncation, is also extended to predict the dynamically drained current and the dynamic power added efficiency (PAE). Finally, a predistortion algorithm for supply-modulated PAs, based on the inversion of the proposed model, is presented.status: publishe

A GaN HEMT Global Large-Signal Model Including Charge Trapping for Multibias Operation

This paper presents a novel empirical model for gallium nitride on silicon carbide high-electron mobility transistors. A global state-space formulation describes charge trapping effects by means of suitable 2-D nonlinear lag functions of the applied voltages, extracted from a reduced set of double-pulse current-voltage characteristics. The implementation in CAD tools involves a simple equivalent circuit and lookup tables, making the model well suited for power amplifier design in the presence of signals of practical interest. An extensive validation at both low (4 MHz) and radio frequencies (5.5 GHz) exhibits good accuracy and a robust performance prediction for the operation above the cut-off of dispersive phenomena, across different operating classes and loads, in terms of output power, power-added efficiency, and third-order intermodulation distortion. These results show that traps with both linear and nonlinear dynamics are stimulated in large-signal operation, and that these must be taken into account for global model predictions

Characterization and Modeling of RF GaN Switches Accounting for Trap-Induced Degradation Under Operating Regimes

This paper describes the performance degradation of RF GaN-on-SiC HEMT switches due to the charge trapping, which is triggered by high voltages under operating regimes. A custom measurement setup is used for the characterization of the switching behavior under dynamic control and blocking voltages. It is shown that both small- [i.e., insertion loss (IL)] and large-signal (LS) performances (i.e., switch compression) are affected by traps. Depending on the applied voltages, an increase of the switch IL up to 50% and significant degradation of the switch compression characteristic were measured for a 4 x 75 \u3bcm\ub2 RF switch in 0.25-\u3bcm GaN-on-SiC technology. These mechanisms cannot be observed with conventional static characterization, and they are not described by standard RF switch models. A device model capable to account for the observed characteristics is identified and empirically validated under LS conditions at 10 GHz

Nonlinear Dynamic Modeling of RF PAs Using Custom Vector Fitting Algorithm

This paper presents an efficient implementation of a first-order modified-Volterra model for radio-frequency power amplifiers. Nonlinear dynamic effects displayed by such systems are described by nonlinear functionals that involve two-variable amplitude-frequency integral kernels. The Vector Fitting algorithm, typically employed for linear systems, is here exploited to provide a decomposition of Volterra kernels into a set of nonlinear static functions of the PA input and corresponding single-pole frequency responses. These are based on a set of global poles that efficiently describe the system dynamics and ultimately lead to a compact model representation. Model implementation results from CAD simulation data are reported for a 6W PA based on a gallium nitride (GaN) transistor