Bandwidth Reduction for Supply Modulated RF PAs Using Power Envelope Tracking

This letter develops a new technique that significantly reduces the bandwidth requirements of the drain supply for an envelope tracked power amplifier (ET-PA). The achieved bandwidth reduction is clearly quantified, and requires almost no processing. The technique is based on developing a drain tracking voltage function that follows the power of the envelope. The use of pure power envelope tracking (PET) results in significant lower bandwidth, with some reduction of efficiency, compared with ET. A second-order PET extension doubles the PET bandwidth and achieves almost the same efficiency as ET. The validity of the PET and the second-order PET is confirmed with measurements on a 2-GHz 10-W GaN PA. The measured results show a bandwidth reduction relative to pure ET of a factor 3 to 8 for PET and 1.4 to 3.8 for the second-order PET. The corresponding efficiencies are 53% and 61.8%, compared with 63% for ET. The linearity is slightly better for PET. All measured with a 16-QAM signal and an average output power of 35.6 dBm.