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An analytic theory for dual-input outphasing power amplifiers that incorporate in one unified treatment, the continuum of solutions for power combining including the Doherty and Chireix modes is presented. This unified theory developed at the current-source reference planes reveals the performance trade-off achieved by all of the possible power amplifier (PA) combiners within the continuum of solutions. Furthermore, it identifies a novel type of dual-input hybrid Chireix-Doherty PA that combines key features of the Doherty and Chireix operations such that the fundamental drain voltages applied to both the main and auxiliary transistors remain constant. This hybrid PA relies on an input outphasing angle varying with the input power level to obtain the correct load modulation behavior. A 2-GHz dual-input hybrid Chireix-Doherty PA is implemented using nonlinear embedding and experimentally evaluated to validate the theory. A drain efficiency of 61% at 9-dB backoff power and a maximum output power of about 43 dBm are obtained for continuous-wave (CW) measurements. The efficiency increases monotonously with output power unlike that of the Doherty PA used for comparison. When excited with a 20-MHz LTE signal with 9.5-dB peak-to-average power ratio (PAPR), the dual-input PA yields a 60.0% average drain efficiency and -48.1-dBc adjacent-channel power-leakage ratio (ACLR) after linearization. 

The use of an active load has been recently proposed for the realization of power-efficient broadband balanced amplifiers. The application of an active load to a dual-input Chireix amplifier is investigated in this paper for the purpose of increasing their bandwidth. An embedding device model is used to established the optimal non-Foster loads required for both the transistors to remain operating in class F as the operating frequency deviates from the center frequency. Given the transistors must operate with a constant voltage swing between backoff and peak, it is found necessary for the two transistors to operate with different load impedances as the frequency varies. The required load impedance and outphasing angles for the Chireix operation are obtained using a generalized eigenvalue problem using the Y-matrix of the Chireix combiner loaded with the active load. It is verified that using an active load, it is possible to maintain a high efficiency not only at peak power but also under various backoff power levels over a bandwidth of 1 GHz. Within a 200 MHz bandwidth, the PA is predicted to be able to maintain an efficiency larger than 79% for 6 dB backoff. Further work is required to experimentally validate the proposed technique. 

Class J has introduced a new rigorous framework for designing broadband PAs. However, the design of broadband Class-J amplifiers remains challenging, as the fundamental impedance termination is non-Foster when the 2 nd harmonic is Foster. In addition the peak instantaneous voltage varies by up to 50% as the frequency changes. In this paper, a generalized Class-J theory is introduced. Then a DC tunable broadband PA with constant instantaneous peak voltage and Foster fundamental and harmonic terminations is proposed.