Third-order nonlinearity compensation in field effect transistors

A method to compensate the field effect transistor (FET) channel third order nonlinearity is proposed and experimentally demonstrated. The FET channel current-voltage (I-V) characteristic is sublinear and hence the related nonlinearity can be compensated by adding the component with superlinear I-V. Such I-V can be realised by using Schottky-type contacts to the FET channel or by connecting the FET to external Schottky diodes. In this reported work, the criterion for non linearity compensation is derived. Next, as a proof of concept, a discrete prototype circuit containing a MOSFET and compensating circuit has been designed, built and tested. As confirmed by two tone measurements, reduction of third-order distortions up to 26 dBm has been achieved by using the nonlinearity compensation network.