Noise Caused by GaAs MESFETs in Optical Receivers

The GaAs metal-semiconductor field effect transistor ( M E S F E T ) originally designed for microwave applications has become an important component of lightwave receivers used in communication applications. Unlike most microwave applications, the lightwave-receiver application requires a consideration of induced gate noise and correlation with the channel noise. Van der Ziel's original evaluation of the noise contribution from this component 1 " 3 was later extended by Baechthold to include effects present in M E S F E T S with short gate length, as well as the intervalley scattering in GaAs.4,5 The following computation extends this earlier work to determine the noise factor r. This factor relates the input noise current int resulting from all noise sources of the F E T to the F E T transconductance g m such that (i2nt) = 4kTT(uCT)2bf/gm, 923 (1)