Fully orthogonal multi-carrier predistortion linearization for RF power amplifiers
This paper presents a fully orthogonal frequency-selective baseband predistortion linearization system for RF multi-carrier power amplifiers (PA) affected by strong differential memory effects. A new scheme is introduced for removing the unwanted inband frequency components generated by the interband predistortion corrections, thus establishing full orthogonality between the interband and inband predistortion. The demonstration study is performed on a two-carrier OFDM signal of 8 MHz bandwidth each, separated by 16 MHz for a total RF bandwidth of 32 MHz. Both the OFDM signal generator and the new orthogonal multi-carrier linearization algorithm proposed were implemented in a field programmable gate array (FPGA) and applied to the experimental investigation of the linearization of a Class AB/Class C LDMOS PA at 3.5 GHz. It is demonstrated that with the new orthogonality implementation, 5 dB inband distortion introduced by the interband predistortion steps is automatically suppressed such that multiple iterative steps between the interband and inband linearizations are no longer required in the optimization. Adjacent channel leakage ratio (ACLR) of up to −45 dBc for inband and interband are demonstrated experimentally.