A 65% efficient envelope tracking radio-frequency power amplifier for orthogonal frequency division multiplex

A high-efficiency radio-frequency (RF) power amplifier (PA) is described for high peak-to-average power ratio (PAPR) orthogonal frequency division multiplexed signals. Envelope tracking is used, where the supply voltage of an RF amplifier is modulated in harmony with the envelope of the RF signal. The envelope modulator is a split-frequency design composed of a switched mode power supply (SMPS) for the low-frequency content, and a hybrid amplifier for the high-frequency part. The hybrid amplifier combines digital switching with a linear amplifier in a transformer coupled push-pull structure. For verification, a 7 dB PAPR 3 MHz bandwidth 3rd generation partnership project long-term evolution (LTE) signal is used. When amplifying the AC component of the LTE envelope signal, 56.2% efficiency is achieved by the hybrid amplifier at 4.6 W output power into a 10 Ω load. Combined with a 94.4% efficient SMPS, the modulator can produce 23.4 W at 83% efficiency. This is combined with an 80.3% efficient 300 MHz RF PA. Together they achieved 65.6% DC-to-RF efficiency at 18.2 W RF output power. The measured PAPR at the amplifier output was 6.5 dB.