Efficiency enhancement method for high-power amplifiers using a dynamic load adaptation technique

This paper proposes a dynamic load adaptation method as an efficiency enhancement technique for high-power amplifiers. This method modifies the output load impedance of a power amplifier using a tunable impedance transformer, so that the efficiency of the power amplifier is not degraded as the power level of the output signal is changed. The tunable impedance transformer presented here consists of a quarter-wavelength transmission line with adjustable characteristic impedance. In addition, an automatic control system is used to control the tunable impedance transformer. The experimental result shows that the efficiency is improved over the entire power range and the adjacent channel leakage power ratio (ACLR) is maintained at less than -30 dBc for a 4-carrier WCDMA signal.