Systematic experimental analysis of an optical sensing microwave low-noise amplifier

This study presents a systematic experimental analysis of the noise figure and the gain of an optical sensing lownoise amplifier (LNA) in the X-band region (8.5–10.5 GHz). The study has been carried out with the purpose of analysing the effects of a 635 nm optical radiation on the gain and noise figure of the LNA, by modifying the bias operating points. Upon varying the bias conditions from those suggested into the component datasheet towards the device pinch-off, the role of the light exposure changes from causing degradation of the gain and noise figure into a clear performance enhancement. In the middle, a bias condition is found where the above LNA parameters become unresponsive to light exposure. Whilst the detrimental role played by the strong gate current increase under light exposure on the noise figure degradation is already clear, the experimental results show that close to pinch-off this effect is completely overcome by the drain current and transconductance increases.