Giorgio Vannini

University of Ferrara | UNIFE · Department of Engineering

In this manuscript, we present a new dynamic-bias measurement set-up and its application to the extraction of a nonlinear model for microwave field-effect transistors. The dynamic-bias technique has been recently proposed and relies on the use of low- and high-frequency vector-calibrated measurements acquired, for instance, by means of a large-sign...

We present the first application of the recently introduced dynamic-bias measurement to the acquisition of the scattering (S-) parameters of microwave transistors under large-signal operating conditions. We demonstrate that by properly acquiring and processing dynamic-bias measurements, one can derive the S-parameters of a nonlinear device-under te...

The purpose of this letter is to present an experimental analysis of the temperature effects on the small-signal equivalent circuit of a GaN HEMT. With the aim of contributing to the exploration and advancement of this technology for high-power and high-temperature applications, the major intrinsic RF figures of merit together with a recently repor...

The term waveform engineering denotes all those circuit design techniques that are based on shaping the transistor voltage and current waveforms. From a general perspective, these design techniques can be grouped in two main categories according to the adopted design tool: measurement- and model-based. In the last two decades, thanks to the prolife...

This paper presents a new approach for the definition and identification of a transistor model suitable for low-noise amplifier (LNA) design. The resulting model is very robust to layout modifications (i.e., source degeneration) providing accurate predictions of device noise-performance and small-signal parameters. Moreover, the described procedure...

This paper describes the efficiency-limiting factors resulting from transistor current source in the case of class-F and inverse class-F (F⁻¹) operations under saturated region. We investigated the influence of knee voltage and gate-voltage clipping behaviors on drain efficiency as limiting factors for the current source. Numerical analysis using a...

In this paper, a single-chip front-end (SCFE) operating in Ku-band (12–17 GHz) is presented. It is designed exploiting a GaN on SiC technology featured by 150 nm gate length provided by UMS foundry. This MMIC integrates high power and low noise amplification functions enabled by a single-pole double-throw (SPDT) switch, occupying a total area of 20...

This work focuses on the equivalent‐circuit modeling of microwave field‐effect transistors. Although the purely direct approach allows obtaining a good prediction accuracy in a straightforward way without the need of any optimization, optimization algorithms are often used to achieve an improved accuracy at the cost of a higher modeling complexity....

In this work, we describe the complete design flow of a 1.3–3.3-GHz active balun, exploited to generate a high-voltage swing differential local oscillator (LO) signal driving a highly linear doubly balanced resistive ring mixer. Both the LO active balun and the mixer are integrated into a Ku -band single chip monolithic microwave integrated circu...

In this paper, a new modeling technique is proposed for extracting small-signal lumped-element equivalent-circuit models for microwave transistors. The proposed procedure is based on using an optimization approach that is improved by targeting a quasi-static behavior as additional objective function rather than only minimizing the error between the...

This letter aims at investigating the impact of the gate width on the microwave field effect transistor (FET) performance, focusing on the GaAs high-electron-mobility transistor (HEMT) technology as a case study. To accomplish this complex task, the small-signal equivalent-circuit elements together with the major RF figures of merit are thoroughly...

Dealing with high-power operation (i.e., >100 W) is extremely critical to power-amplifier designers due to the lack of accurate transistor models of multicell (i.e., powerbar) devices. The reason is twofold: from one side, it is extremely difficult to characterize high-power transistors (e.g., device instability, thermal issues, microwave instrumen...

The upcoming technologies related to Internet of Things will be characterized by challenging requirements oriented toward the most efficient exploitation of the energy in electronic systems. The use of wireless communications in these devices makes this aspect particularly important, since the performance of radio transceivers is strongly dependent...

The aim of this feature article is to provide a deep insight into the origin of the kink effects affecting the output reflection coefficient (S22) and the short-circuit current-gain (h21) of solid-state electronic devices. To gain a clear and comprehensive understanding of how these anomalous phenomena impact device performance, the kink effects in...

In this article, we report on the temperature-dependent GaN HEMT behavior. To evaluate the potentialities of this kind of active solid-state electronic device at its best, the experiments are performed at extreme operating conditions. As a case study, we consider a large 0.25-μm GaN HEMT with a gate periphery of 1.5 mm, providing a high dissipated...

Driven by the fast‐growing demand for high‐frequency applications, electronics engineers are steadily pushing transistor technologies beyond their high‐frequency limits. A key figure of merit to quickly assess the potential of a transistor for high‐frequency applications is given by the cut‐off frequency (fT) that is defined as the frequency at whi...

GaN FETs have achieved superior performance in the design of microwave power circuits. Nevertheless, the amount of dispersion related to this technology poses severe issues for the correct modeling and characterization of these devices. In this letter, the effects of GaN FET dispersion on the design of power amplifiers (PAs) with dynamic power supp...

This letter is aimed at discovering and analyzing anomalous phenomena affecting millimeter-wave FETs, focusing on a GaN HEMT as a case study. For the first time, we show that the real parts of the impedance parameters can increase and then decrease with frequency, due to the resonance of the extrinsic reactive elements. This resonance may be detect...

In this paper we apply for the first time the nonlinear-embedding technique to the design of power amplifiers based on laterally-diffused metal-oxide-semiconductor (LDMOS) field-effect transistors (FETs). Such a design technique is based on setting the transistor load line at the intrinsic current-generator plane, according to well-known theoretica...

Starting from the mathematical bases of waveform engineering, this contribution demonstrates the effectiveness of class-F power amplifier design in different bias conditions, provided the correct harmonic content is presented at the input. To validate the theoretical assumptions, low-frequency multiharmonic load-pull measurements are carried out on...

In this paper, we present a measurement setup for characterizing high-voltage high-power microwave transistors in terms of their reliability under actual operating conditions. By operating in the megahertz range, one exploits important advantages as the use of low-cost instrumentation and the possibility of handling high voltages and high powers. F...

This study focuses on temperature dependent characterization of a 0.25x1500 m2 GaN HEMT. The impact of the ambient temperature on the microwave performance is reported and discussed. It is achieved that the reduction of the average electron velocity with increasing temperature leads to a remarkably degradation of the main figures of merit.

In this paper, we present an ultra-wideband six-port junction adopted as an impedance sensing board for the Internet of Things and the fifth-generation wireless communication systems. We designed, fabricated, and tested the six-port junction in the frequency range from 5 GHz to 6 GHz. Moreover, the sensing board functionality is fully validated wit...

In this paper an automated measurement system for the investigation of degradation phenomena in GaN FETs is presented. The system is able to perform both static and dynamic stress cycles under actual device operation, gathering useful information strictly related to the “health” of the device. As case study a 75-VDC GaN HEMT was used for a 19-hours...

An innovative approach in RF GaN technology suitable for Global Positioning System (GPS) L-band transmitters is presented. The solution operates directly from the 100 VDC voltage bus without the need for a DC-DC step-down converter to typical 28 V or 50 V. It is based on a mature GaN HEMT process which is radiation tolerant and reliable for space a...

The first chapter is meant to give a comprehensive overview of the fundamentals, state-of-the-art, challenges, and future trends in the field of high-frequency transistor modeling. Linear, as well as noise and nonlinear operations, are dealt with. The importance of microwave transistor modeling comes from the fact that the transistor is the key com...

The Nonlinear Vector Network Analyzer (NVNA) is the workhorse for nonlinear measurements. Also, during the development of new communications systems, such as 5G, dedicated test equipment is not available. Sampling and real-time oscilloscopes offer a lower cost alternative to the NVNA but require error corrections to improve their accuracy. NPL, NIS...

The first chapter is meant to give a comprehensive overview of the fundamentals, state-of-the-art, challenges, and future trends in the field of high-frequency transistor modeling. Linear, as well as noise and nonlinear operations, are dealt with. The importance of microwave transistor modeling comes from the fact that the transistor is the key com...

In this paper, we describe an extraction procedure of nonlinear models for microwave field-effect transistor (FET). We use a nonlinear model available in commercial CAD tools, and we extract the parameters by combining direct extraction and numerical optimization. We determine a first estimate of the model parameters by few DC and S-parameter measu...

The purpose of this invited paper is to give readers a comprehensive and critical overview on how to extract equivalent-circuit models for GaN HEMTs, which are the preferred devices for high-power high-frequency applications. This overview is meant to provide a practical modeling know-how for this advanced type of transistor, in order to support it...

We extend the recently proposed dynamic-bias measurement technique to the identification of non-quasi-static FET models. In particular, we propose to exploit two high-frequency tickles superimposed on the low-frequency large-signal excitation. The tickle frequencies are chosen in order to separately extract the quasi-static and non-quasi-static mod...

As well as largely exploited for microwave high-power applications, aluminum gallium nitride (AlGaN)/GaN high electron mobility transistor (HEMT) technologies have demonstrated promising results for the design of low-noise, high dynamic range, and highly robust amplifiers. In this manuscript, we describe the design and characterization of a Ku-band...

Gallium Nitride (GaN) transistors are increasingly attracting the attention of the microwave research community due to their performance in terms of power density and frequency capabilities. As a matter of fact, GaN is considered as the leading technology for future telecom and space applications. Nevertheless, nonlinear modelling of GaN transistor...

This contribution aims at the experimental confirmation of the advantages of the harmonic manipulation theory, using a low-frequency low-cost characterization setup. A 0.5-µm 10x100-µm (1-mm gate periphery) GaN HEMT has been characterized synthesizing at the current-generator plane different load conditions, realizing tuned-load and Class-F operati...

In this paper a small-signal and noise transistor model with the associated extraction procedure is proposed. The model is based on an equivalent circuit, extracted from electromagnetic simulations and noise measurements using an automatic analytical procedure. This identification procedure ensures high robustness to layout modifications, making th...

In this work, the design of a C-band class-AB power amplifier based on the waveform engineering approach is presented. The design leverages the low-frequency characterization of the transistor to obtain the prediction of its optimum operating condition. An exhaustive validation of the realized amplifier fully validates the proposed design technique...

In this work, the design of a C-band class-AB power amplifier based on the waveform engineering approach is presented. The design leverages the low-frequency characterization of the transistor to obtain the prediction of its optimum operating condition. An exhaustive validation of the realized amplifier fully validates the proposed design technique...

Gallium nitride high electron-mobility transistors have gained much interest for high-power and high-temperature applications at high frequencies. Therefore, there is a need to have the dependence on the temperature included in their models. To meet this challenge, the present study presents a neural approach for extracting a multi-bias model of a...

This letter provides a clear understanding of the kink effect in for active solid-state electronic devices. The origin of the kink effect is ascribed to the intrinsic section of the transistor, whereas the extrinsic elements determine its shape at the extrinsic ports. Therefore, to fairly compare the kink effect for GaN and GaAs HEMTs, the present...

In this paper the nonlinear model of a GaN transistor is extracted starting from dynamic bias measurements under class-F operation. Thanks to this technique, applied for the first time to high-efficiency classes of operation, one can get at once and separately the nonlinear currents and charges of the transistor in actual operating conditions. As c...

A nonlinear multi-bias model oriented to accurately predict the effects of charge-trapping in Gallium Nitride (GaN) HEMTs is proposed. As a case study, we considered a 0.25-µm 8x75-µm GaN HEMT. The model is identified by using CW low-frequency time-domain data and validated through high-frequency vector nonlinear measurements.

The extraction of a high-frequency ivalent circuit model plays a fundamental role for the development of any emerging transistor technology. Indeed, an equivalent circuit can provide a valuable support for microwave engineers to ensure a fast and reliable optimization of both device fabrication and circuit design. As far as gallium nitride (GaN) HE...

In the paper, the nonlinear model of a microwave transistor is extracted from large-signal measurements acquired under “dynamic-bias” operation. Specifically, the transistor is driven by low-frequency large signals while a high-frequency tickle is applied on top of them. The low-frequency large signals, along with the dc bias voltages, set the larg...

In this paper, an experimental validation about the benefit of the input harmonic manipulation on the performance of a microwave power amplifier is presented. With the support of low-frequency measurements on a 0.5×1000 μm2 GaN HEMT, the importance of synthesizing the correct input waveform at the intrinsic section of the device is highlighted. A c...

A scalable HEMT noise model has been developed, based on a lumped parasitic network extracted analytically through full-wave electromagnetic simulations and a scalable black-box representation of the intrinsic noise and AC response of the device. The analytical extraction of the lumped parasitic network is extensively explained, as well as the intr...

In this paper a recently proposed identification procedure based on exciting the device under test simultaneously with low-frequency (LF) large-signal excitations and a high-frequency tickle tone, is applied for the first time to GaN transistors. It will be demonstrated that the proposed technique allows reaching good prediction capability even whe...

In this paper, an experimental validation about the benefit of the input harmonic manipulation on the performance of a microwave power amplifier is presented. With the support of low-frequency measurements on a 0.5×1000 μm2 GaN HEMT, the importance of synthesizing the correct input waveform at the intrinsic section of the device is highlighted. A c...

SUMMARY In this paper, a nonlinear model of a commercial 10-W laterally diffused metal oxide semiconductor (LDMOS) transistor for FM transmitters is identified. It is based on high-frequency small-signal measurements for the identification of both the parasitic network and the strictly nonlinear dynamic effects, whereas low-frequency large-signal m...

In this letter we extract the parameters of the charge equations of a microwave transistor nonlinear model which is available in commercial CAD tools. In particular, the charge model parameters are extracted starting from small- and large-signal measurements. A better accuracy can be achieved when using large-signal measurements since the model par...

A X-band GaN monolithic microwave integrated circuits (MMIC) High Power Amplifier (HPA) suitable for future generation Synthetic Aperture Radar systems is presented. The HPA delivers 14 W of output power, more than 38% of PAE in the frequency bandwidth from 8.8 to 10.4 GHz. Its linear gain is greater than 25 dB. For the first time an MMIC X-band HP...

We extract the nonlinear model of a 0.15 μm GaAs pHEMT for cold-FET mixer applications. The model parameters are extracted from experimental data obtained by simultaneously driving the device under test with low-frequency large signals and a tickle tone at the RF operating frequency. The advantage of this approach is twofold. Firstly, as a result o...

In this paper a characterization technique for the evaluation of transistor performance and restrictions is presented, based on a simple and low-cost measurement system. Experimental examples, carried out on a 0.5 × 1000 μm2GaN HEMT, are reported. The validity of the proposed approach is demonstrated by comparing the results with the ones obtained...

In this paper an artificial neural network approach for nonlinear modelling of a 10-W LDMOSFET is presented. The model extraction is based on DC and scattering parameter measurements. In particular, artificial neural networks are used to model the dependence of both DC drain current and intrinsic capacitances with respect to the intrinsic gate and...

In this paper, an empirical characterization technique of charge-trapping effects in GaN FETs based on low-frequency measurements is proposed. It is applied on a 0.25 × 600 μm2GaN HEMT. Experimental results confirm theoretical assumptions reported in literature.

This paper, for the first time, analyzes in detail the kink phenomenon in ${ S}_{22}$ as observed in GaN HEMT technology. To gain a comprehensive understanding, the kink effect (KE) is studied with respect to temperature and bias conditions. The achieved results clearly show that the dependence of the KE on the operating condition should be mainly...

This work presents a straightforward approach aimed at modeling the dynamic I–V characteristics of microwave active solid-state devices. The drain-source current generator represents the most significant source of nonlinearity in a transistor and, therefore, its correct modeling is fundamental to predict accurately the current and voltage waveforms...