The University of Messina Microwave Electronics Lab (EleMIC) uses NI AWR Design Environment software for research and all microwave electronics education levels (B.S., M.S., Ph.D.). The challenge for Prof. Caddemi is to not only introduce her students to the secrets of microwave circuit analysis and design but also to make it a truly exciting experience.
Of particular interest to Prof. Caddemi is device modeling. In this domain, she and her group have 25 years of experience and more than 200 international papers published. A tough benchmark has been the design of single-stage, high-power microwave amplifier using complex device models for nonlinear analysis of the device behavior as well as optimization. The group recently used Microwave Office circuit design software to tune the behavior of a gallium arsenide (GaAs) high-electron mobility transistor (HEMT) wafer previously characterized in the microwave range (2-18 GHz) under dark and laser-light illuminated conditions. A key challenge was the noise analysis and modeling aspect that was markedly changed by the light exposure.
The Solution
NI AWR Design Environment fulfills the EleMIC’s requirements for having very agile software tools to accomplish the fine tuning required for model refinement, complete and versatile nonlinear analysis tools, and easy management of layout generation for EM simulation. For the work presented in the IEEE conference paper, the software was used to analyze 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 was then 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 was evaluated.
On the basis of device performance variations under VIS light exposure, either a severe degradation of the noise figure, a slight increase of the amplifier gain, or a moderate variation of the input/output matching was expected. 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. NI AWR Design Environment was then used to analyze the correlation between the device model variations and the amplifier behavior to get a deeper insight into the observed trends.
On the basis of measured results, a low-noise amplifier was tailored on the device performance in dark conditions. The design was carried out Microwave Office, with performance goals centered in the 7.5 to 8.5 GHz frequency band. Alumina (εr = 9.9, tg δ = 0.0002, h = 250 μm) was adopted for the substrate with 5 µm-thick gold metallization. The amplifier gain is above 10 dB, while the noise figure is 1.4 ± 0.15 dB over the entire band. Either input and output matching levels stay higher than 10 dB within the chosen frequency band. The stability was monitored either inside and all over outside the operating band by the value of coefficient. Modeling of the bonding wires has been accomplished by means of the resident multilevel bond wire model BWIRES2 that define bonding scheme parameters in compliance with EIA/JEDEC Standard No. 59.
Due to the required stabilization of the amplifier, we noticed that the reflection coefficient “seen” on the left side of the device input was not really close to Γopt within the operating band, i.e., broad-band stabilization was achieved at the expense of the noise mismatch.
