Dynamic linearisation overcoming sweet spot of Doherty amplifier for WiBRO handset

Abstract

A dynamic predistorter is applied to a Doherty amplifier to obtain high linearity and efficiency for operation with multi-frequency-allocation WiBRO services. The non-linear path uses a reflection-type dynamic predistorter comprising common collector InGaP/GaAs HBTs operated at saturation. A 40-dB range of intermodulation signal is obtained, which overcomes the peaking amplifier inter-modulation transfer characteristic. At the same time, the Doherty amplifier having an unbalanced signal is based on the low-loss transistor cell-combining techniques, and it is used to make a carrier amplifier operated towards P1 dB within the range satisfying linearity for WiBRO in consideration of efficiency. The spurious emission characteristics are compatible with WiBRO standards up to an output power of 22 dB m for multi-frequency allocation. The efficiency is 21% at 22 dB m.