A 2.655 GHz 3-stage Doherty power amplifier using envelope tracking technique

We demonstrates an optimized design of a highly efficient 3-stage Doherty PA for the 802.16e Mobile world interoperability for microwave access(WiMAX) application at 2.655-GHz. The ‘3-stage’ Doherty PA is the most efficient architecture among the various Doherty PAs for a high peak to average power ratio(PAPR) signal. However, due to the low quiescent bias point of the peaking PA, it has an improper load modulation problem, which causes over saturated operation of the carrier PA and insufficient peak power. We have solved the problem using a gate envelope tracking(ET) technique. For the WiMAX signal with a 7.8 ∼ 8.5 dB PAPR and 20-MHz instantaneous bandwidth, the measured efficiency of the proposed 3-stage Doherty PA has been maintained 56.7 % at an average output power of 43.3 dBm, a 7.2 dB backed-off output power from peak output power level. These experimental results clearly show that the 3-stage Doherty with ET technique has a superior efficiency with high peak power.