On the choice of optimum FET size in wide-band transimpedance amplifiers

The main figure of merit for transimpedance amplifiers used in amplifying photocurrents in fiber-optics systems is the optical sensitivity. This sensitivity is determined by the equivalent input noise current of the amplifier. To obtain the best noise performance, most transimpedance amplifiers with FET input stages are designed using a result that prescribes making the capacitance of the input FET equal to the photodiode capacitance. It is shown that this is not necessarily the most favorable practice when using FETs in scaled submicrometer technologies. For example, it may compromise the stability of the amplifier.>