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Efficiency Improvement of a Handset WCDMA PA Module Using Adaptive Digital Predistortion

From Skyworks Solutions, Inc.

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.

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