Who we are

Electronics for Telecommunications Research Laboratory

The Research Group 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).
Research work has been carried out by developing approaches in the frame of state-of-the-art research subjects and in the context of national and international research projects.
In 1991, a numerical technique for the efficient intermodulation analysis of non-linear microwave circuits [1] was developed which demonstrated, under mild approximations, an enormous improvement in terms of computing effort (i.e., simulation time and memory occupation) making it feasible circuit analyses otherwise impossible on workstations available at that time. The basic idea was that of exploiting the double periodicity of the two-tone excitation, jointly with a quasi-stationary hypothesis, to decouple the Harmonic Balance equations. Similar concepts were later probed further by other researchers 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).

Since 1987, when many researchers were fighting with non-linear equivalent circuits for GaAs MESFETs, pioneering research was carried out on non-linear black-box modelling approaches for microwave electron devices, initially dealing with “Describing Functions”-like models. However, was the study of some milestone techniques for the modelling of non-linear dynamic systems (Volterra’s work and successive developments) which opened the way to the definition in 1992 of a new “Non-linear Integral Model” (NIM) [2]. This was probably the first electron device model to directly exploits suitable device measurements, in conjunction with a sound prediction formula, to compute the device non-linear dynamic response.
It can be said that different new concepts and approaches were introduced with the NIM: the adoption of a behavioral approach to the non-linear modelling of microwave devices, the introduction of a “measurement-based” model, the definition of a “Non-linear Integral Series” [3] of which the famous Volterra series is a particular case. It is interesting to observe that the paper on the NIM was re-discovered fifteen years later, in 2006-07, by several authors dealing with behavioral models.
Research carried out at that time was founded interesting by the European Space Agency: two research projects related to Non-linear Integral Modelling and dispersion modelling of III-V FETs were supported between 1992 and 1996 .
At the end of eighties, researchers in the field of non-linear microwave electron device modelling became conscious of the troubles caused by “traps” (and thermal effects). In 1993 a new non-linear modelling approach was developed [4], [5] 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. Recently, new developments have been obtained by introducing a thermal dependence in the traps status [6].

The development of millimetre-wave applications and related MMICs has offered new jobs to people working on device modelling and CAD tool development. Lumped elements descriptions are not able to capture all the parasitic, coupling and distributed effects present at high operating frequencies or in highly complex MMICs. The development of numerical techniques and the availability of low-cost computer resources made it affordable at the end of nineties the numerical solution of the electromagnetic and electron transport problems in a consistent way. However, such an approach was clearly not viable for MMIC design. As an alternative, in 1999, an empirical distributed modelling approach based on the EM (Method of Moments) simulation of the electron device layout was introduced [7]. Ten years later the same approach is being still successfully adopted to model Cascode FETs for the design of distributed travelling wave amplifies [8].
Presently, original research is being carried out by pursuing new characterization, modelling and design approaches. As low-frequency (LF) dispersive effects still cause headaches in III-V technologies (especially with the advent of GaN transistors), different pulsed setups are currently being commercialized for I/V device characterization. Their cost and complexity are increasing due to more and more higher voltage and current operations required. Nevertheless, electron device characterization is carried out in a regime (pulsed) which is strongly different from actual operating conditions (sinusoidal or distorted sinusoidal). As a viable and low-cost alternative to pulsed measurement systems, a two-source LF setup for dynamic I/V transistor characterisation under sinusoidal excitations has been developed [9,10]. This low-frequency load-pull setup has been effectively exploited to obtain an in-depth dynamic I/V characterization which in conjunction with a look-up table description of the device capacitances has been successfully adopted for high-power GaN amplifier design [11].

The Research Group has been widely involved also in HMIC and MMIC design. In particular, different circuits were designed in cooperation with several industrial, research and academic partners: X-band MMIC Doppler sensor, highly-linear cold-FET mixers, 20GHz GaAs HFET and 35 GHz GaAs PHEMT power amplifiers, X-band HBT and PHEMT power amplifiers, L-band GaN high-power amplifiers, wideband PHEMT LNAs, X-band MMIC DROs and push-push VCOs, Silicon 2.4GHz power amplifiers and X-band DRO oscillators, etc..
Research in this field 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".

KEY REFERENCES
[01] 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.
[02] 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.
[03] 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.
[04] 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.
[05] 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.
[06] 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.
[07] 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.
[08] 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.
[09] A.Raffo, V.Vadalà, P.A.Traverso, A.Santarelli, G.Vannini, F.Filicori. “A Dual-Source Nonlinear Measurement System Oriented to the Empirical Characterization of Low-Frequency Dispersion in Microwave Electron Devices”, Computer Standards and Interfaces Journal, Special Issue of XVI IMEKO, to be published 2010.
[10] 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.
[11] 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.