A simple mixer for generating the 3rd-order intermodulation products used for HPA predistortion

This paper proposes to use nonlinear mixer circuits to generate the intermodulation (IM) products for high-power amplifier (HPA) predistortion using the difference-frequency technique. The design of a 3rd-order nonlinear circuit is used for illustration purpose. The circuit employs two mixers using Schottky diodes as non-linear devices to generate the difference-frequency signals. The circuit has a simple structure, requires no DC bias or additional filters, and is easy to fabricate and low cost. Simulation and measurement results show that the design has a low conversion loss and a low-frequency spurious.