Increasing the talk-time of mobile radios with efficient linear transmitter architectures

Abstract

Power efficiency of the RF transmitter stage in mobile handsets has a direct impact on battery capacity as well as talk-time between battery recharge cycles. Unfortunately the power amplifier (PA) linearisation methods in common usage today to meet the linearity specification of standards such as GSM EDGE, TETRA and UMTS result in low DC to RF efficiency. This paper discusses the relationship between linearity and transmitter efficiency and reviews various linearisation schemes: Cartesian loop, polar loop, 2nd harmonic injection, envelope elimination and restoration (EER), predistortion methods, and synthesis techniques (e.g. LINC and CALLUM). The paper also shows that to increase the power efficiency (and thus talk-time) hybrid solutions to power amplifier linearisation are required and these are also discussed.