Dynamic output phase to adaptively improve the linearity of power amplifier under antenna mismatch

We present the development of a new adaptive circuit that preserves the performance of a power amplifier (PA) under impedance mismatch caused at the antennas. The circuit includes a phase detector and a phase shifter that dynamically provide the optimal phase of the reflection coefficient at the output of the PA, to achieve the optimal performance under mismatch. Using this technique, the power amplifier maintains its performance close to that at 50 Ω, even under severe mismatch of VSWR 10:1. A 900 MHz CDMA GaAs power amplifier achieves an improvement of 6.4 dB in IP3 and 6.9 dB in the P_1dB in a high power mode (28.5 dBm) at a VSWR of 10:1. The same PA in low power mode (18.6 dBm) has improvement of 4.35 dB in IP3 and 2.3 dB in P_1dB at a VSWR of 10:1. A SiGe PA at 2.4 GHz using the adaptive technique shows an improvement in IP3, by 5.8 dB, and in P_1dB, by 4.5 dB, at a VSWR of 20:1.