An RF transmitter with optimal control of amplifier bias with respect to efficiency and adjacent channel power

摘要

A mobile 'phone transmitter includes an RF amplifier 18 gain-stabilized by a feedback loop 22,26,28,14. The adjacent channel leakage ratio (ACLR) of the output signal 24 is computed in control circuit 20 (figures 2 or 3) and the bias input of the amplifier 18 is then adjusted so that the ACLR (ACPR) is met but not significantly exceeded, thereby ensuring compliance with ACLR standards while minimising power consumption. The ACLR ratio is computed using logarithmic generators (figures 2 or 3). The ACLR ratio may be computed as (a) the ratio of the total output power to the adjacent channel power or (b) the ratio of the desired channel power to the adjacent channel power. The feedback loop maintains the output level despite alteration of the amplifier's gain due to bias changes.