This paper presents a new way of designing multi-mode switchable power amplifier without relying on any extra tuning elements. By operating the RF GaN transistor as a switch (digital) or amplifier (analog), it enables three different modes within a quadrature-balanced load-modulation architecture, including series/parallel Doherty and hybrid load modulated balanced amplifier (H-LMBA), which can be optimally configured according to different load conditions. Based on this new method, an intrinsically mode-switchable load-modulation PA is designed with GaN transistors and branch-line quadrature coupler at 1.7 GHz. Together with the unique harmonic-tuned method, the nominal mode of H-LMBA (for matched condition) achieves a high-order load modulation with > 62% measured efficiency across a 10-dB output back-off (OBO) range. Efficient performance is also demonstrated at series/parallel Doherty modes, which are configured with exchangeable main/auxiliary roles and dedicated switch settings offering mismatch resilience.
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Pseudo-Doherty Load-Modulated Balanced Amplifier With Wide Bandwidth and Extended Power Back-Off Range
This article presents a novel architecture of load-modulated balanced amplifier (LMBA) with a unique load-modulation characteristic different from any existing LMBAs and Doherty power amplifiers (DPAs), which is named pseudo-Doherty LMBA (PD-LMBA). Based on a special combination of control amplifier (carrier) and balanced amplifier (peaking) together with proper phase and amplitude controls, an optimal load-modulation behavior can be achieved for PD-LMBA, leading to maximized efficiency over extended power back-off range. More importantly, the efficiency optimization can be achieved with only a static setting of phase offset at a given frequency, which greatly simplifies the complexity for phase control. Furthermore, the cooperations of the carrier and peaking amplifiers in PD-LMBA are fully decoupled, thus lifting the fundamental bandwidth barrier imposed on the Doherty-based active load modulation. Upon theoretical proof of these discoveries, a wideband RF-input PD-LMBA is physically developed using the GaN technology for experimental demonstration. The prototype achieves a highly efficient performance from 1.5 to 2.7 GHz, e.g., 58%–72% of efficiency at 42.5-dBm peak power and 47%–58% at 10-dB output back-off (OBO). When stimulated by a 10-MHz long term evolution (LTE) signal with a 9.5-dB peak-to-average power ratio (PAPR), the developed PD-LMBA achieves an efficiency of 44%–53% over the entire bandwidth at an average output power of around 33 dBm.
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- Award ID(s):
- 1914875
- NSF-PAR ID:
- 10186657
- Date Published:
- Journal Name:
- IEEE Transactions on Microwave Theory and Techniques
- Volume:
- 68
- Issue:
- 7
- ISSN:
- 0018-9480
- Page Range / eLocation ID:
- 3172 - 3183
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1109/TMTT.2020.2983925
