Andrea Nalli

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.

GaN HEMT Noise Model Based on Electromagnetic Simulations

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 is very robust since it does not require any numerical optimization, with possibly related problems like local minima and unphysical model parameters. The adopted model topology is based on a lumped element parasitic network and a black-box intrinsic device, which are both identified on the basis of full-wave electromagnetic simulations, as well as noise and S-parameter measurements. The procedure has been applied to three GaN HEMTs having different peripheries and a Ku-band LNA has been designed, demonstrating a very good agreement between measurements and predicted results.

Linear versus nonlinear de-embedding: Experimental investigation

The manuscript presents a comparison between nonlinear and linear de-embedding procedures for the identification of the I/V dynamic characteristics at the transistor current-generator plane. These approaches, without the need for modeling device trapping and thermal effects, allow to retrieving the waveforms of the electrical quantities at the current generator that governs device performance in terms of output power and efficiency. It will be demonstrated that the accuracy of the selected procedure determines the accuracy of the obtained results. Simulations and measurements carried out on a 0.25 × 600 μm2 GaN HEMT are reported as case study.

Evaluation of FET performance and restrictions by low-frequency measurements

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 by means of commonly adopted measurement setups.

Extremely low-frequency measurements using an active bias tee

An active bias tee suitable for small- and large-signal low-frequency (5 Hz to 400 kHz) characterization of electron devices has been designed and manufactured. Different experimental results, carried out on 0.25 μm GaAs and GaN HEMTs, confirm the validity of the proposed bias circuit.

GaN HEMT modelling through 50-Ω NF measurements

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 the model suitable for low-noise amplifier design. An equivalent temperature approach is exploited for noise modelling: every passive element of the equivalent circuit is considered at room temperature, except for the intrinsic drain conductance. Its equivalent temperature is extracted by simply fitting the noise figure for a 50 Ω source termination. The proposed technique allows a very good accuracy of the noise parameter predictions for degenerated devices, avoiding expensive and time consuming noise parameter characterization.

Characterization of charge-trapping effects in GaN FETs through low-frequency measurements

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.

Identification of the optimum operation for GaN HEMTs in high-power amplifiers

In this paper, a technique for the prediction of the optimum performance operation of GaN transistors is described. It is based on a small set of low-frequency measurements to acquire the I/V dynamic behavior of the device and a “partial” model to consider the strictly nonlinear dynamic effects of the device. The technique is applied and validated on a 0.5-8×250-μm2 GaN HEMT at 5.5 GHz.