Optimized Envelope Tracking Operation of Doherty Power Amplifier for High Efficiency Over an Extended Dynamic Range

Abstract

This paper presents an optimized envelope tracking (ET) operation of a Doherty amplifier. Compared to the general ET/envelope elimination and restoration transmitter, it has an advantage of the extended dynamic range of 6 dB for the load modulation of a Doherty amplifier. Moreover, by modulating the supply voltage of the carrier amplifier, while that of the peaking amplifier is fixed, the supply modulator provides just half of the current for the same power amplifier output power. It results in a reduced chip size and the crest factor of the supply modulating signal is reduced by 6 dB, enhancing the efficiency of the supply modulator. The designed ET transmitter consisting of the Doherty amplifier and the supply modulator are fabricated in 2-mu m HBT and 0.13-mu m CMOS processes, respectively. It presents the efficiency improvement over the broad output power region. Especially at the 16-dB backed-off power level, more than 23% of power-added efficiency (PAE) is achieved. For WiBro application, it shows the PAE of 38.6% at an output power of 24.22 dBm with a gain of 24.62 dB. The error vector magnitude is 3.64%.