Design of Microwave GaAs MESFET’S for Broad-Band Low-Noise Amplifiers

As a basis for designing GSAS MESFET’S for broad-band low-noise mnpfMe~ tbe fundarnentaf relationships between basic device parmnete~ sod two-port noise parameters are investigated in a semiempfrfcaf manner. A set of four noise parameters are shown as sfmple functfons of equivalent circuit elements of a GaAs MESFET. Each element fs then expressed in a simple anafytfcai form with the geometrical and material parameters of this device. Thus practical expressions for the four noise parameters are developed in terms of the geometrical and nmterfsf parameters. Among the four noise parameters, the rnfnfmum noise figure Finn, and equfvafent noise resistance R., are considered crucial for broad-band Iow-nofse arnpfffiem. A low Rn corresponds to less sensitivity to input rnismatc~ and can be obtained with a short heavily doped thin active channel. Such a high channel doping-twtbickness (N/a) ratio has a potential of producing high power gain, but is contradictory to obtaining a low Ftin. Thmeforq a compromise in choosing N and a is necmsary for beat overaif amplifier performance. Foor nnrnerfcai examples are given to show optfrnfsatfon pmceseea.