Sergio Di Falco

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.

X-Band GaN Power Amplifier for Future Generation SAR Systems

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 HPA has been designed by directly measuring the transistor behavior at the current generator plane. In particular, optimum device load-line has been selected according to the chosen performance tradeoffs.

A new approach to Class-E power amplifier design

An innovative, recently introduced, methodology for microwave power amplifier design, is here extended to switching-mode Class-E amplifier operation. Such a technique is based on a complete and accurate electron device (ED) characterization, which is provided by both direct large-signal low-frequency I/V measurements, performed by means of a relatively simple low-cost setup, and a model-based description of nonlinear reactive effects related to ED capacitances. In order to verify the proposed design methodology, a Class-E power amplifier (PA) has been designed.

Analysis of the gate current as a suitable indicator for FET degradation under nonlinear dynamic regime

Abstract Electron device degradation, although not directly accounted for, represents a key issue in microwave circuit design. This is especially true when the particular applications involved (e.g., satellite, military, consumer) do not allow or strongly discourage any kind of maintenance. As a matter of fact, in order to account for device degradation in circuit design, a suitable electron device model is needed which is able to predict the performance degradation as a function of the actual electrical regime involved in the device operation. Such a kind of model is not available in literature. In this paper, quantitative results are provided for device degradation indicators which correlate DC and RF stress experiments. These results can be considered an important step toward the definition of a nonlinear model accounting for device degradation.

GaN HEMT large-signal model accounting for both low-frequency dispersion and high-frequency non-quasi-static effects

The extraction of an accurate model for GaN HEMT devices is of fundamental importance for high-power amplifier design. In particular, the model should be able to reproduce the microwave device behaviour under realistic operating conditions. In light of that, we present a technique for extracting a large-signal GaN HEMT equivalent circuit, which includes both low-frequency dispersive phenomena and high-frequency non-quasi-static effects.

GaN power amplifier design exploiting wideband large-signal matching

The present manuscript details a wideband high power amplifier design, based on a 5-mm GaN power bar. In particular, a broadband input large-signal matching condition has been realized, that ensures optimal power transfer under actual device operation. The measured performance of the PA perfectly matches the expected predictions based on large-signal measurements carried out on a 1.25-mm GaN elementary cell.