Efficient and wideband envelope amplifiers for envelope tracking and polar transmitters

Envelope tracking provides the potential for achieving high efficiency in power amplifiers for next generation wireless transmitters with high peak-to-average ratio signals such as OFDMA. Envelope modulators with high fidelity, high efficiency and wide bandwidth are critical enablers for the widespread application of envelope tracking. This presentation reviews the development of various envelope amplifiers for applications in basestation and handset power amplifiers. Requirements of voltage swing, bandwidth, and accuracy are first described. Various technologies for envelope modulators achieving voltages as high as 50V are presented, for operation in basestations with Si-LDMOS, HVHBT, GaN RF power transistors. CMOS-based Si envelope modulator ICs for operation in wireless handsets are also discussed. Envelope tracking microwave power amplifiers that achieve overall efficiency greater than 45% for LTE in handsets and greater than 64 % efficiency in basestations are presented.