Efficiency improvement of a handset WCDMA PA module using Adaptive Digital Predistortion

Adaptive Digital Predistortion (DPD) is applied to a spec-compliant class-AB GaAs HBT PA module for WCDMA handsets. It is shown that, by using a re-optimized load line, the efficiency can be increased from 37.5% to 47% at nominal 28.5 dBm output power, while maintaining the same excellent linearity of the original PA. The quiescent current consumption is also reduced down to 40 mA at all power levels, enabling up to 49% average dc power savings without dynamic biasing. Under 2∶1 VSWR, 7% to 11% higher PAE is demonstrated at 28 dBm, achieving significant ACPR reduction as well. The methodology to tradeoff the linearization capability of DPD to optimize efficiency at a specified power and linearity is discussed in detail.