Design Of MESFET Optical Amplifier

GaAs MESFETs, originally designed for microwave applications, have become an important com ponent of receivers in high-speed optical telecommunication systems. For these applications, the crucial point in the device modeling is the evaluation of the induced gate noise and its correlation to the channel noise. In this paper the design of a low-noise small signal optical amplifier using GaAs MESFET is carried out. The principal noise sources of GaAs MESFETs are analyzed in order to completely characterize the equivalent model. Particularly channel-noise represents the dominant effect in the determination of the optical receiver sensitivity. Total input noise current of the optical amplifier, due to correlated gate and drain MESFET noise, has been estimated in order to evaluate the excess channel-noise factor r for different values of photodiode capacitance. This procedure allowed to choose the photodiode with minimum noise. At last, scattering parameters, minimum noise gain, gain-frequency dependence and bandwidth of the amplifier have been evaluated in the frequency range of interest.