Envelope tracking RF power amplifier design

Abstract

In modern wireless communication systems, the requirement of achieving high data rates results in non-constant envelope signals with high peak to average power ratio (PAPR). However, the operation of conventional power amplifiers (PAs) at back-off power levels creates significant degradation in efficiency. Since efficiency is a critical design consideration for PAs to avoid high power consumption and heating problems, several techniques were introduced to maintain the high efficiency for a wide range of power levels. We designed an envelope tracking power amplifier (ETPA) that uses the supply modulation technique which is a promising solution to the efficiency degradation problem. In ETPA, the high efficiency is maintained at back-of levels by adjusting the supply voltage in accordance with the time varying signal envelope. The supply voltage was efficiently generated by using a synchronous buck converter operating at 10 MHz switching frequency. The converter was integrated to the designed class-AB PA by using a proper low pass filter. In order to improve the signal bandwidth that can be tracked, an envelope bandwidth elimination algorithm was used. The efficiency of the resulting ETPA system was measured as 26% for the signal that has 3 MHz bandwidth and 12 dB PAPR. The system has an efficiency of 20% with the signal that has 5 MHz bandwidth and 13 dB PAPR.