Load Modulated Balanced Amplifier Design Method Based on Complex Impedance Trajectories

This paper presents a design methodology for load modulated balanced amplifier (LMBA) focusing on AMPM distortion mitigation. By introducing second harmonic control as degree of freedom, complex trajectory can be selected to compensate nonlinearities in the device without substantially affecting efficiency. A mathematical derivation is accompanied by procedure based closed-form equations fabricate an LMBA solely load-pull data. The theory validated through measured comparison three different designs operating at 2.4 GHz pseudo-RF-input Doherty-like configuration, with class-J, -B, and -J* main PAs. class-J prototype outperforms other 54% 49% drain efficiency peak output power 6-dB back-off, respectively, only 4 degrees AM-PM across this range. When driven 10-MHz, 8.6-dB PAPR LTE signal, 40.5% average achieved better than $-40.5$ dBc ACLR digital predistortion.