Memory Correction ofaDoherty PowerAmplifier with aWCDMA Input using Digital Predistortion

A digital predistortion algorithm ispresented that compensates forseverenonlinearities and memoryeffects introduced byahighefficiency RF poweramplifier (PA)witha Doherty structure. Theinput signal, multi-carrier WCDMA, has a widebandwidth andlarge crestfactor thatstimulates the nonlinear modesofthePAandgenerates significant out-of-band distortion. The predistortion usesfiltered nonlinear modes, derived fromtheinputsignal, to reducetheout-of-band distortion. Computationally efficient two-stage filters are implemented usingstatic filters chosen tomatchthestatistical properties oftheWCDMA signal followed byasmaller setof adaptive FIR coefficients. Theestimation favors out-of-band distortion avoiding biases inthepredistortion coefficients dueto quadratureimbalances. The algorithmperformance, demonstrated onatestbenchincluding aDoherty PA,exceeds theACLR specifications Illandprovides asmuchas29dBof distortion reduction. IndexTerms- Amplifier distortion, communication system nonlinearities, poweramplifier linearization, poweramplifiers.