Waveform Engineered Sequential Load Modulated Balanced Amplifier With Continuous Class-F⁻¹ and Class-J Operation

This article presents a novel waveform engineered sequential load modulated balanced amplifier (W-SLMBA) that uses a continuous Class-F ⁻¹ control amplifier (CA) to manipulate the impedance trajectory of the balanced amplifier (BA). It is demonstrated that the use of the continuous Class-F ⁻¹ CA can trigger a unique impedance load modulation mechanism by which the fundamental impedance of the BA is shaped by the varying second-harmonic load reactance of the CA. Theoretical derivations reveal that this special load modulation yields extended design space for the LMBA, in which high efficiency can be achieved over wide bandwidth and output power back-off (OPBO). A prototype operating from 1.80 to 2.75 GHz is designed following the proposed theory. The implemented LMBA achieves a measured drain efficiency (DE) of 60.2%–68.3% at saturation and 51.8%–69.0% at 8-dB OPBO. When tested with a 100-MHz long-term evolution (LTE) signal having peak-to-average power ratio (PAPR) of 8 dB, the proposed LMBA achieves 50.2%–59.1% average DE and better than −45.1-dBc adjacent channel power ratio (ACPR) across the target bandwidth after digital predistortion (DPD).