# Who we are

** Electronics for Telecommunications Research Laboratory**

The Research activity dates back to the end of eighties. Different topics related to the Computer Aided Design of RF and microwave integrated circuits have been dealt with: non-linear electron device modelling and characterisation, numerical techniques for non-linear circuit analysis, design methodologies for non-linear circuits (mixers, oscillators and power amplifiers).

**1987** - Pioneering research was carried out on non-linear black-box modelling approaches for microwave electron devices, initially dealing with “Describing Functions”-like models, and successively studying the modelling of non-linear dynamic systems (Volterra’s series) [1].

**1990** -The “Non-linear Integral Model” (NIM) [2,3] has been proposed. This was probably the first electron device model to directly exploit suitable device measurements to compute the device non-linear dynamic response. Different new concepts were introduced with the NIM: the behavioral approach to the non-linear transistor modelling, the introduction of a “measurement-based” model, and the definition of a “Non-linear Integral Series” [4] of which the famous Volterra series is a particular case. Interestingly, the paper on the NIM was re-discovered fifteen years later by several authors dealing with behavioral models.

**1991** - Development of a new numerical technique for the efficient intermodulation analysis of non-linear microwave circuits [5,6,7] which demonstrated an enormous improvement in terms of simulation time and memory occupation, making it feasible circuit analyses otherwise impossible on workstations available at that time. The basic idea was later exploited to develop numerical techniques for the analysis of non-linear circuits under digitally modulated excitations (e.g., Envelope Circuit Simulation introduced in 1995 by HP, now Agilent Technologies).

**1993** - At the end of eighties, troubles caused by “traps” and thermal effects in III-V transistors become evident. A new non-linear modelling approach was developed [8], [9] which comprehensively dealt with traps and thermal effects by clearly introducing concepts still adopted nowadays for the modelling of I/V dynamic characteristics in III-V FETs. Research in this field has been going on with a number of papers published [e.g. [10]), also on GaN technologies [11].

**1999** - MMIC millimeter-wave applications show the limitations of lumped-element transistor models (poor description of coupling, parasitic and distributed effects). In such a context, an empirical distributed modelling approach based on EM (Method of Moments) simulations of the electron device layout was introduced [12]. Later, the same approach has been successfully adopted to model Cascode FETs [13] and for GaN noise models [14].

**2005** – A new low-frequency dynamic I/V measurement system is developed [10] that will put the basis for the research activity in the following years. This system is a valuable alternative to the use of pulsed I/V measurements for the characterization of dispersive effects (in GaN transistors in particular) [15]. It has been successively exploited for transistor modeling [10,11,16], reliability testing [17] and of for the design of power amplifiers [18,19].

**2008** – Research on transistor modeling is going on: different issues related to equivalent circuit models [20,21,22] and thermal dependence [23,24] are dealt with.

**2009** – The low-frequency dynamic I/V characterization system evolves toward a fully-automated load-pull system [15] and an associated design technique for power amplifiers is proposed [18]. Moreover, “nonlinear embedding/de-embedding” techniques [25,26] are investigated as well as their application [19,27,28].

**2011** – Advanced nonlinear and dynamic-bias measurement techniques are applied in the context of electron device modeling [29,30,31,32,33].

**2017** - Research contracts with GaN power transistor manufacturers and GaN foundries (transistor characterization and modeling, implementation of the LFLP setup - Low-Frequency Load-Pull) [34].

**2019** - High-power multicell GaN transistor models are developed [35].

Research activity was also devoted to HMIC and MMIC design in cooperation with several industrial, research and academic partners: X-band MMIC Doppler sensor, highly-linear cold-FET mixers, 20 GHz GaAs HFET and 35 GHz GaAs PHEMT power amplifiers, X-band HBT and PHEMT power amplifiers, L- and X-band GaN high-power amplifiers, wideband PHEMT LNAs, DROs and push-push VCOs, etc..

Research work has been carried out in the context of national and international research projects, and also led to the foundation of the academic spin-off MEC srl in 2004.

In 1995, 1998 and 2001, papers presented at the 25th European Microwave Conference, GAAS98 and GAAS2001, respectively, received the "Best Paper Award".

**MAIN REFERENCES**

[01] F.Filicori, V.A.Monaco, G.Vannini, “Mathematical approaches to electron device modelling for non-linear microwave circuit design: state of the art and present trends”, European Transactions on Telecommunications and related technologies, Vol.1, n.6, pp.641-653, December 1990, invited.

[02] F.Filicori, G.Vannini, “Mathematical approach to large-signal modelling of electron devices”, Electronics Letters, Vol.27, n.4, pp.357-358, February 1991.

[03] F.Filicori, G.Vannini, V.A.Monaco, “A nonlinear integral model of electron devices for HB circuit analysis”, IEEE Trans. on Microwave Theory and Techniques, special issue on “Process oriented CAD and modelling”, Vol.40, n.7, pp.1456-1465, July 1992.

[04] D.Mirri, G.Iuculano, F.Filicori, G.Pasini, G.Vannini, G.Pellegrini, “A modified Volterra series approach for nonlinear dynamic system modelling”, IEEE Trans. on Circuits and Systems I, Vol.49, n.8, pp.1118-1128, August 2002.

[05] F.Filicori, V.A.Monaco, G.Vannini, “Computationally efficient multitone analysis of non-linear microwave circuits”, Proc. of the 21st European Microwave Conference, Stuttgart, Germany, pp.1550-1555, September 9-12, 1991.

[06] G. Vannini, F. Filicori, P.A. Traverso, “Tool for efficient intermodulation analysis using conventional HB packages", Electronics Letters, Vol.35, No. 17, pp. 1415-1416, August 1999.

[07] A. Costantini, P.A. Traverso, G. Vannini, “Power amplifier ACPR simulation using standard Harmonic balance tools”, IEEE ISCAS, International Symposium on Circuits and Systems, Scottsdale, Arizona, USA, May 26-29, 2002.

[08] F.Filicori, G.Vannini, A.Mediavilla, A.Tazon, “Modelling of deviations between static and dynamic drain characteristics in GaAs FETs”, Proc. of 23rd European Microwave Conference, Madrid, Spain, pp.454-457, September 6-9, 1993.

[09] F.Filicori, G.Vannini, A.Santarelli, A.Mediavilla, A.Tazon, Y.Newport, “Empirical modelling of low-frequency dispersive effects due to traps and thermal phenomena in III-V FETs”, IEEE Trans. on Microwave Theory and Techniques, Vol.43, n.12, pp.2973-2981, December 1995.

[10] A.Raffo, A.Santarelli, P.A.Traverso, G.Vannini, F.Palomba, F.Scappaviva, M.Pagani, F.Filicori, “Accurate PHEMT Nonlinear Modeling in the Presence of Low-Frequency Dispersive Effects”, IEEE Trans. on Microwave Theory and Techniques, Vol.53, no.11, pp., Nov 2005.

[11] A.Raffo, V.Vadalà, D.Schreurs, G.Crupi, G.Avolio, A.Caddemi, G.Vannini, "Nonlinear Dispersive Modeling of Electron Devices Oriented to GaN Power Amplifier Design", IEEE Trans. On Microwave Theory and Techniques, April 2010.

[12] A.Cidronali, G.Collodi, G.Vannini, A.Santarelli, G.Manes, “A new approach to FET model scaling and MMIC design based on electromagnetic analysis”, IEEE Trans. on Microwave Theory and Techniques, Vol.47, no.6, pp. 900-907, June 1999.

[13] D.Resca, J.A.Lonac, R.Cignani, A.Raffo, A.Santarelli, G.Vannini, F.Filicori, “Accurate EM-based Modelling of Cascode FETs”, IEEE Trans. On Microwave Theory and Techniques, April 2010.

[14] A.Nalli, A.Raffo, G.Crupi, S.D’Angelo, D.Resca, F.Scappaviva, G.Salvo, A.Caddemi, G.Vannini, “GaN HEMT Noise Model Based on Electro-Magnetic Simulations”, IEEE Trans. On Microwave Theory and Techniques, Aug 2015.

[15] A.Raffo, S.Di Falco, V.Vadalà, G.Vannini, “Characterization of GaN HEMT Low-Frequency Dispersion Through a Multi-Harmonic Measurement System”, IEEE Trans. On Microwave Theory and Techniques, Sept 2010.

[16] A.Raffo, G.Bosi, V.Vadalà, G.Vannini, “Behavioral Modeling of GaN FETs: a Load-Line Approach”, IEEE Trans. On Microwave Theory and Techniques, Jan 2014.

[17] A.Raffo, V.Di Giacomo, P.A. Traverso, A.Santarelli, G.Vannini, "An Automated Measurement System for the Characterization of Electron Device Degradation under Nonlinear Dynamic Regime", IEEE Trans. on Instrumentation and Measurements, Aug 2009.

[18] A.Raffo, F.Scappaviva, G.Vannini, “A New Approach to Microwave Power Amplifier Design Based on the Experimental Characterization of the Intrinsic Electron-Device Load-line”, IEEE Trans. On Microwave Theory and Techniques, July 2009.

[19] D.Resca, A.Raffo, S.Di Falco, F.Scappaviva, V.Vadalà, G.Vannini, “X-Band GaN Power Amplifier for Future Generation SAR Systems”, IEEE Microwave and Wireless Components Letters, April 2014.

[20] G. Crupi, D. Schreurs, A. Raffo, A. Caddemi, G. Vannini, “A New Millimeter Wave Small-Signal Modeling Approach for pHEMTs Accounting for the Output Conductance Time Delay”, IEEE Trans. on Microwave Theory and Techniques, April 2008.

[21] G.Crupi, D.Schreurs, A.Caddemi, A.Raffo, F.Vanaverbeke, G.Avolio, G.Vannini, W.De Raedt, “High-Frequency Extraction of the Extrinsic Capacitances for GaN HEMT Technology”, IEEE Microwave and Wireless Components Letters, Jul 2011.

[22] G.Crupi, A.Raffo, A.Caddemi, G.Vannini, “Kink Effect in S22 for GaN and GaAs HEMTs”, IEEE Microwave and Wireless Components Letters, May 2015.

[23] Z.Marinkovića, G.Crupi, A.Caddemi, G.Avolio, A.Raffo, V.Marković, G.Vannini, D.Schreurs, “Neural Approach for Temperature Dependent Modeling of GaN HEMTs”, International Journal of Numerical Modelling: Electronic Networks, Devices and Fields, July 2015.

[24] G. Crupi, A. Raffo, G. Avolio, D. Schreurs, G. Vannini, A. Caddemi, “Temperature Influence on GaN HEMT Equivalent Circuit”, IEEE Microwave and Wireless Components Letters, 2016.

[25] V.Vadalà, G.Avolio, A.Raffo, D.Schreurs, G.Vannini, “Nonlinear Embedding and De-embedding Techniques for Large-signal FET Measurements”, Microwave and Optical Technology Letters, Dec 2012.

[26] A. Raffo, V. Vadalà, and G. Vannini, “Nonlinear Embedding and De-embedding: Theory and Applications”, in “Microwave De-embedding: From Theory to Applications”, ISBN 978-0124017009, Academic Press, Oxford, 2013.

[27] V.Vadalà, A.Raffo, S.Di Falco, G.Bosi, A.Nalli, G.Vannini, “A Load-Pull Characterization Technique Accounting for Harmonic Tuning”, IEEE Trans. On Microwave Theory and Techniques, July 2013.

[28] A. Raffo, V. Vadalà, G. Bosi, F. Trevisan, G. Avolio, G. Vannini, “Waveform Engineering: State-of-the-Art and Future Trends”, INVITED PAPER, International Journal of RF and Microwave CAE, 2016.

[29] G.Avolio, D.Schreurs, A.Raffo, G.Crupi, I.Angelov, G.Vannini, B.Nauwelaers, “Identification technique of FET model based on vector nonlinear measurements”, Electronics Letters, Vol.47, n.24, p.1323–1324, Nov 2011.

[30] G.Avolio, A.Raffo, I.Angelov, V.Vadalà, G.Crupi, A.Caddemi, G.Vannini, D.Schreurs, “Millimetre-wave FET Nonlinear Modelling Based on the Dynamic-Bias Measurement Technique”, IEEE Trans. On Microwave Theory and Techniques, 2014.

[31] G. Avolio, A. Raffo, V. Vadalà, G. Vannini, D. Schreurs, “Dynamic-Bias S-parameters: A New Measurement Technique for Microwave Transistors”, IEEE Trans. On Microwave Theory and Techniques, 2016.

[32] V. Vadalà, A. Raffo, G. Avolio, M. Marchetti, D. Schreurs, G. Vannini, "A New Dynamic-Bias Measurement Setup for Nonlinear Transistor Model Identification", IEEE Trans. On Microwave Theory and Techniques, 2017.

[33] A. Raffo, G. Avolio, V. Vadalà, G. Bosi, G. Vannini, D. Schreurs, "Assessing GaN FET Performance Degradation in Power Amplifiers for Pulsed Radar Systems”, IEEE Microwave and Wireless Components Letters, 2018.

[34] K. Kikuchi, H. Yamamoto, N. Ui, K. Inoue, V. Vadalà, G. Bosi, A. Raffo, G. Vannini, “Comparison of GaN HEMT Technology Processes by Large-Signal Low-Frequency Measurements”, INMMIC 2018, Brive-La-Gaillarde, France, July 5-6, 2018.

[35] A. Raffo, V. Vadalà, H. Yamamoto, K. Kikuchi, G. Bosi, N. Ui, K. Inoue, G. Vannini, “A New Modeling Technique for Microwave Multicell Transistors Based on EM Simulations”, IEEE Trans. On Microwave Theory and Techniques, 2020.