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.