Modeling of low noise amplifier using optically gated MOSFET

In any communication system, noise gets added with the signal at receiver end. Noise figure is one of the measures of performance of a receiver circuit with respect to noise. It is seen that receiver circuits are employed with FET devices due to low power consumption, low cost and high package density. With this paper LNA design of Optically Gated MOSFET (OGMOSFET) is carried out as LNA is the first building block of any receiver circuit. LNA is designed for narrow band of 2-3 GHz. Modeling of optical interaction in LNA is presented. Simulation is carried out for single ended LNA in MATLAB. Noise figure is plotted against different W/L and found minimum for W/L=0.35μm. MOSFET having length of 0.35μm is selected for design which is optically gated with incident optical power of 0.25mW and wavelength of 800nm. Inversion level of OGMOSFET increases under illumination. Prime goal of LNA design is noise reduction. Noise figure of LNA is computed under dark and illumination. Result shows that the noise figure of LNA employing OGMOSFET (illuminated gate) reduces significantly as compare to conventional MOSFET (dark).