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

Abstract

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).

Mitigation of Load Mismatch Effects Using an Orthogonal Load Modulated Balanced Amplifier

“…This is a different approach compared to those presented in the papers discussed above since it can provide good RF bandwidth, and does not place any tunable component directly in the path of the output signal, hence relaxing the requirements in terms of losses and power handling. This paper also differs from previous work on LMBA [46]- [54] and OLMBA since it shows for the first time the ability to compensate for load mismatch using the OLMBA architecture.…”

Broadband Sequential Load Modulated Balanced Amplifier With Extended Design Space Using Second Harmonic Manipulation

“…Because there is no load modulation in the carrier branch, the CM CA can be designed to provide high efficiency at OBO over a wide bandwidth. Using the continuous Class-F −1 CA, the design space of the fundamental impedance of the BA can be extended by varying the second-harmonic load impedance of the CA [35], [36]. The recently reported hybrid asymmetrical load modulated balanced amplifier (H-ALMBA) also used harmonic-controlled output matching networks (OMNs) for the realization of hybrid continuous Class-F/F −1 CA operation in carrier branch [37].…”

“…In theory, the bandwidth of both the LMBA and SLMBA configurations is only constrained by the bandwidth of the input and output quadrature couplers [26], [33], [34], [38], [39]. However, in practice, the active devices of CA and BA cells require proper source/load fundamental or harmonic impedance tuning to achieve high efficiency with broadband operation [32], [35], [36], [37], [40], [41], [42], [43], [44], [45], [46]. Although the CM theory provides PA design with high-efficiency broadband load design continuum, a fundamental limitation exists that most of the practical This work is licensed under a Creative Commons Attribution 4.0 License.…”

“…Case studies show that the combination of different OBO input driving levels and normalized CA secondharmonic voltage can provide the BA peaking branch with multiple sets of expanded fundamental design space (i.e., either along constant resistance contour or resistively extended contours). Different from the previous work on waveform engineered sequential load modulated balanced amplifier (W-SLMBA) [35], this work focuses on the further extension of broadband operation without deteriorating high efficiency at either OBO or saturation level.…”

Modular Design and Characterization of a Reconfigurable Sequential Power Amplifier

“…The rapid deployment of the fifth-generation (5G) communication systems imposes significant challenges in radio frequency (RF) power amplifier (PA) design due to the required high data rates and societal needs for energy efficiency [1]. Moreover, 5G waveforms present high peak-to-average power ratio (PAPR) in the range from 9 to 15 dB which further degrades the PA efficiency [2], and hence PAs with efficient output power back-off (OPBO) characteristics are required, complementing other energy saving mechanisms in our quest for green communications technologies. Conventional single transistor PAs can achieve the peak efficiency only at the maximum output power.…”