Practical EVM Optimization of 802.11ac Wi-Fi Transmitters via Load-Pull Measurements

Abstract

A practical approach to optimizing the error vector magnitude (EVM) performance of RF transmitters in RF transceivers is presented based on the load-pull measurement. The optimization of EVM performance at the output of the transmitter on an evaluation board (EVB) under small- and large-signal operating conditions is achieved upon the output matching load impedance. Optimization of the S11-parameter of the load-pull is determined based on the minimum EVM while generating the output power as large as possible. Then, an optimal matching circuit consisting of LC components at the output of the transmitter is designed and tuned through the National Instrument (NI) AWR design software to achieve the same S11 parameter as the measured S11. Such LC parameters are then applied to the output matching circuit of the 5-GHz Wi-Fi transmitter and the measured EVM with the optimal impedance is better than that with a 50 Ohm impedance.