General noise considerations for Gigabit rate NMOS FET front end design for optical fiber communication systems.

Receiver design noise considerations for FET front ends for fiber optics amplifiers as presented by Smith and Personick are revisited. The MOSFET noise model used is simple yet more accurate than that used previously in the above reference. The device equivalent circuit for noise is derived from first principles. We are thus able to optimize the amplifier sensitivity with respect to hot carrier channel thermal noise in terms of the FET drain to source voltage and the effective channel length. The importance of drain/source overlap capacitance in determining amplifier sensitivity is also quantified. It is thus concluded that in spite of hot carrier noise effects, fine line NMOS amplifiers designed for Gigabit rate applications will continue to see sensitivity improvement for effective channel lengths down into the quarter micron range. Investigation in the subquarter micron range is in progress.