Non-linear distortion in gallium arsenide MESFET control and switch circuits

GaAs MESFETs offer significant advantages over conventional PIN diodes in many RF and microwave control applications. However, the MESFET shows significant non-linearities that can affect its circuit performance at power levels less than 30 dBm, in contrast with the PIN diode which may be used to control kilowatts of power. It is therefore necessary to determine the MESFET non-linear behavior so that meaningful comparisons may be made against PIN diodes in similar control applications. The author presents a small-signal non-linear model for the MESFET, which is then used in a discussion of those MESFET parameters controlling distortion in switch and attenuator applications. In addition, those factors controlling distortion that also play a role in governing the power handling and switching figure of merit in control MESFETs are discussed. The non-linear MESFET model is compared with a previously published non-linear PIN diode model under identical circuit conditions. The non-linear MESFET model is verified with experimental data of second and third order harmonic distortion intercept point