NOISE IN DISTRIBUTED MESFET PREAMPLIFIERS

The theory of noise in a distributed MESFET preamplifier is developed. From this, it is shown that the equivalent input noise current densit y of a distributed preamplifier of an optical receiver can be improved by using large gate line matching impedance and appropriate scaling o f the MESFET width. A front-end tuning circuit was designed using filt er theory to further improve the noise performance of the preamplifier . A monolithic GaAs MESFET distributed preamplifier was fabricated wit h on chip front-end tuning components. Using a 35 mu m InGaAs p-i-n ph otodiode, the preamplifier was shown to have an equivalent input noise current density of 8 pA/root Hz and an 8 GHz bandwidth. To date, this is the best known result for a 0.8 mu m GaAs MESFET process.