A Power-Recycling Technique for Improving Power Amplifier Efficiency Under Load Mismatch

This letter presents a method for improving the efficiency of a power amplifier (PA) under load mismatch by recycling the reflected power. By configuring the PA as a balanced PA, the reflected power will be directed to the isolation port of a 90^° hybrid coupler. The reflected power can then by rectified and converted back to dc power to assist in supplying the PA. A prototype system was built to validate the concept and tested under various load phase angles with 2:1 and 4:1 VSWR using a W-CDMA voice signal at 836.5 MHz. Measurement results show that the power recycling technique improves the overall efficiency by as much as 22.1% when the output power level is 25 dBm. Under load conditions and power levels where the rectifier cannot provide sufficient output voltage level to supply the PA, the proposed technique simply maintains the original PA efficiency with no degradation.