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

Power efficiency of the RF transmitter stage in mobile handsets has a direc t impact on battery capacity as well as talk-time between battery recharge cycles. Unfortunately the power amplifier (PA) linearisation methods in com mon usage today to meet the linearity specification of standards such as GS M EDGE, TETRA and UMTS result in low DC to RF efficiency. This paper discus ses the relationship between linearity and tranmitter efficiency and review s various linearisation schemes: Cartesian loop, polar loop, 2nd harmonic i njection, envelope elimination and restoration (EER), predistortion methods , and synthesis techniques (e.g. LINC and CALLUM). The paper also shows tha t to increase the power efficiency (and thus talk-time) hybrid solutions to power amplifier linearisation are required and these are also discussed.