Giorgio Vannini

A nonlinear integral model of electron devices for HB circuit analysis

A technology-independent large-signal model of electron devices, the nonlinear integral model (NIM), is proposed. It is rigorously derived from the Volterra series under basic assumptions valid for most types of electron devices and is suitable for harmonic-balance circuit analysis. Unlike other Volterra-based approaches, the validity of the NIM is not limited to weakly nonlinear operation. In particular, the proposed model allows the large-signal dynamic response of an electron device to be directly computed on the basis of data obtained either by conventional measurements or by physics-based numerical simulations. In this perspective, it provides a valuable tool for linking accurate device simulations based on carrier transport physics and harmonic-balance circuit analysis algorithms. Simulations and experimental results, which confirm the validity of the NIM, are also presented. >

Nonlinear Dispersive Modeling of Electron Devices Oriented to GaN Power Amplifier Design

This paper presents a new modeling approach accounting for the nonlinear description of low-frequency dispersive effects (due to thermal phenomena and traps) affecting electron devices. The theoretical formulation is quite general and includes as particular cases different models proposed in the literature. A large set of experimental results, oriented to microwave GaN power amplifier design, is provided to give an exhaustive validation under realistic device operation.

Empirical modeling of low-frequency dispersive effects due to traps and thermal phenomena in III-V FET's

An empirical approach is proposed which accounts for low-frequency dispersive phenomena due to surface state densities, deep level traps and device heating, in the modeling of the drain current response of III-V FETs. The model, which is based on mild assumptions justified both by theoretical considerations and experimental results, has been applied to GaAs MESFETs of different manufacturers. Experimental and simulation results that confirm the validity of the model are provided in the paper.<<ETX>>

A New Approach to Microwave Power Amplifier Design Based on the Experimental Characterization of the Intrinsic Electron-Device Load Line

This paper presents a new original approach to power amplifier design, which is mainly based on low-frequency nonlinear empirical electron device (ED) characterization. The proposed technique enables the same level of accuracy provided by expensive load-pull measurement systems to be obtained through a relatively simple and low-cost setup. Moreover, ED currents and voltages related to reliability issues can be directly monitored. Different experimental examples based on power GaAs and GaN field-effect transistors are provided to demonstrate the validity of the proposed approach.

A New Millimeter-Wave Small-Signal Modeling Approach for pHEMTs Accounting for the Output Conductance Time Delay

A new technique is developed for determining analytically a millimeter-wave small-signal equivalent-circuit model of GaAs pseudomorphic HEMTs from scattering parameter measurements. In order to obtain a good agreement between model simulations and measurements up to 90 GHz, the conventional intrinsic output conductance is substituted by a voltage-controlled current source with a time delay. Consequently, a simple and accurate extraction procedure is proposed for taking into account the introduction of the output conductance time delay.

Characterization of GaN HEMT Low-Frequency Dispersion Through a Multiharmonic Measurement System

In this paper, the experimental characterization of low-frequency dispersion (i.e., long-term memory effects) affecting microwave GaN HEMTs is carried out by adopting a new nonlinear measurement system, which is based on low-frequency multiharmonic signal sources. The proposed setup, which has been fully automated by a control software procedure, enables given source/load device terminations at fundamental and harmonic frequencies to be synthesized. Different experimental results are provided to characterize well-known effects related to low-frequency dispersion (e.g., knee walkout and drain current collapse) and to demonstrate the validity of assumptions commonly adopted for electron device modeling.

Behavioral Modeling of GaN FETs: A Load-Line Approach

In this paper, a new model formulation is presented that correctly accounts for low-frequency dispersion (i.e., trapping and thermal phenomena) affecting field-effect transistors (FETs). In particular, for the first time a behavioral description is applied only to the intrinsic current generator, enabling the correct measurement-based evaluation of the intrinsic device operation. The model, which is by construction technology independent, has been extensively validated considering a GaN FET. This choice is justified by the large interest around this technology and by the presence of dispersion effects that must be accurately accounted for.

Scalable Nonlinear FET Model Based on a Distributed Parasitic Network Description

Electron device modeling requires accurate descriptions of parasitic passive structures connecting the intrinsic electron device to the external world. In conventional approaches, the parasitic phenomena are described by a network of lumped elements. As an alternative, a distributed description can be conveniently adopted. This choice has been proven very appropriate when dealing with device scaling and very high operating frequencies. In this paper, a novel approach to distributed parasitic modeling is adopted for the very first time in association with a nonlinear electron device model. In particular, it is shown how an equivalent intrinsic device and a suitably defined distributed parasitic network can be accurately defined and modeled on the basis of standard measurements and easy electromagnetic simulations. Wide experimental validation based on GaAs pseudomorphic HEMTs is provided, showing accurate prediction capabilities both under small- and large-signal conditions. The proposed model is shown to perform optimally even after periphery scaling.

Scalable Equivalent Circuit FET Model for MMIC Design Identified Through FW-EM Analyses

A scalable approach to the modeling of millimeter- wave field-effect transistors is presented in this paper. This is based on the definition of a lumped extrinsic parasitic network, easily scalable with both the number of fingers and the finger widths. The identification of the extrinsic network parameters is carried out by means of accurate full-wave electromagnetic simulations based on the layout of a single reference device. In the paper, the parasitic effects of the gate/drain manifolds and of the source layout are investigated, leading to the definition of realistic linear scaling rules. The obtained model is experimentally validated by using a family of 0.25-mum millimeter-wave GaAs pseudomorphic HEMTs through the accurate prediction of critical performance indicators, such as the linear maximum power gain or the stability factor. Despite the simplicity of the proposed model, it proves to be as accurate as typical scalable models provided by foundries. Straightforward application of the scalable modeling approach to the optimum device geometry selection in a typical design problem is also presented.

A Load–Pull Characterization Technique Accounting for Harmonic Tuning

A novel methodology for the characterization of the nonlinear dynamic behavior of electron devices (EDs) is presented. It is based on a complete and accurate ED characterization that is provided by large-signal low-frequency I/V measurements, performed by means of a low-cost setup, in conjunction with any model-based description of the nonlinear reactive effects related to ED capacitances. The unique feature of the proposed technique is that a fully harmonic control of waveforms at the current generator plane is achieved, and as a consequence, high-efficiency operation can be simply investigated. Different experimental data are presented on GaAs and GaN transistors, and to definitely verify the capability of the new approach, the design of a class-F GaN power amplifier is deeply investigated as a case study.