Analysis of GaAs MESFET spectrum regeneration driven by a /spl pi//4-DQPSK modulated source

A new method of analyzing transistor nonlinearity in the context of digital modulation is proposed. Classical methods of nonlinearity analysis, such as the third-order intercept point, are ill-suited for systems based on digitally modulated signals. The third-order intercept point ignores higher-order effects and latent out-of-channel power, both of which affect spectrum regeneration. Using a power spectral density description of the source, coupled with a simplified Volterra series model of a GaAs MESFET, it is shown that reactive nonlinearity contributes to spectrum regeneration. Subsequently, insight is gained at the device level for doping/implant improvements and at the terminal level for optimal loading, resulting in improved linearity.<>