Phase nonlinearity of buried-layer GaAs MESFET´s

Linearity has been investigated at powers below saturation both for GaAs MESFET´s having specially tailored buried-layer doping profiles and for conventional GaAs MESFET´s. Buried-layer doping profile devices exhibit-linearity equivalent to a third-order intermodulation distortion coefficient M3of -94 dB at 6 GHz at 1 wats output power for 8 mm gate-width devices. The phase component is almost eliminated as compared both to the phase component of conventional devices and to the gain component, and it alone corresponds to an M3of < -99 dB under the same conditions. In conventional (uniformly-doped-channel) MESFET´s it is found that nonlinearity is caused by nonlinear input capacitance which gives rise to phase distortion, as shown experimentally and by numerical calculations.