Giuseppe Salvo

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.

Remarks of an Extensive Investigation on the Microwave HEMT Behavior Under Illumination

This letter presents valuable remarks based on an extensive experimental study of the microwave behavior for a GaAs HEMT under CW infrared and visible laser exposure. The comparison of both dc and microwave (scattering and noise) parameters with and without illumination has highlighted that the device behavior is significantly affected by the light exposure. The observed optical effects can be ascribed to the threshold voltage shift originating from the internal photovoltaic effect. The light sensitivity has shown to be more pronounced at shorter wavelength.

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.

Performance analysis of a microwave low-noise amplifier under laser illumination

This paper analyzes in detail the performance changes of a GaAs HEMT-based low-noise amplifier under visible (650 nm) laser exposure. The device employed was first characterized in dark and illuminated conditions over the 2-18 GHz frequency range in terms of DC, scattering and noise parameters. Subsequently, it was modeled by means of a linear circuit model with associated noise sources in both conditions. By employing the experimental results, a low noise amplifier has then been designed and optimized for dark mode operation in the 7.5-8.5 GHz frequency range. Finally, the performance of the LNA under light exposure has been evaluated. On the basis of the device performance variations under VIS light exposure, we expected either a severe degradation of the noise figure, a slight increase of the amplifier gain and a moderate variation of the input/output matching. Instead, the obtained results exhibited a moderate degradation of the overall LNA performance due to device illumination, except for the input matching level which showed to be improved. We then analyzed the correlation between the device model variations and the amplifier behavior to get a deeper insight into the observed trends.

Analysis of microwave noise parameters of scaled AlGaAs/GaAs HEMT's under light exposure

In this work, the results of an extensive experimental analysis of on wafer AlGaAs/GaAs HEMTs under CW visible laser exposure are presented. The DC and 2-26.5 GHz small-signal performances of scaled gatewidth (100, 200, 300 μm) with and without illumination have been deeply investigated and compared with the results previously reported in the literature. In addition, the noise parameter variations in the 2-18 GHz range have been analyzed. The observed effects exhibit a marked dependence from the light exposure especially in terms of the minimum noise figure and the optimum noise reflection coefficient. The effects of the laser illumination are clearly related to a threshold voltage shift, due to the internal photovoltaic effect, which resulted to be the predominant response process related to CW optical power absorption. As a general trend, the light sensitivity has shown to be more pronounced in the smallest device for either DC and microwave (scattering and noise) parameters.