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
Load-Modulating Loop Combiner for Linear Power Amplification
This work presents a novel power amplifier (PA) architecture employing a feedforward-like loop structure for the linearization of a load-modulated PA. The load-modulating loop combiner (LMLC) is related to a feedforward amplifier, but with the interaction between the main and auxiliary amplifiers to generate both distortion cancellation and load modulation. A brief overview of the underlying theory is presented, followed by a hardware demonstrator operating at 3.5 GHz with 42-dBm peak output power and 55% peak drain efficiency in CW. When excited by a 100-MHz LTE signal, it maintains a 3-ppt EVM improvement and a 2–5-ppt average drain efficiency improvement compared to its standalone main amplifier.
more »
« less
- Award ID(s):
- 1846507
- NSF-PAR ID:
- 10386688
- Publisher / Repository:
- IEEE Microwave and Wireless Technology Letters
- Date Published:
- Journal Name:
- IEEE Microwave and Wireless Components Letters
- Volume:
- 33
- Issue:
- 2
- ISSN:
- 1531-1309
- Page Range / eLocation ID:
- 1 to 3
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
This work presents a novel approach for reducing the out-of-band distortion generated in a concurrent dualband power amplifier (PA) without penalty to output power or efficiency using a filter between a driver amplifier and final-stage PA that manipulates the driver amplifier out-of-band distortion such that the overall distortion of the cascade is minimized. The cascaded PA operates at 2.4-GHz and 3.5-GHz with peak output power and drain efficiency of 41.6/40.4 and 65.2/55.1 respectively. The filter reduces the out-of-band distortion of the cascade when excited by dual 10-MHz LTE-like signals by 10 dB while improving average drain efficiency by 5 percentage points.more » « less
-
Waleed Khalil (Ed.)The increasing performance demanded by emerging wireless communication standards motivates the development of various techniques devoted to improving the efficiency of power amplifiers (PA) because this is one of the most power-demanding blocks in RF transceivers. Power-amplifier efficiency is proportional to the ratio of the average voltage delivered by the PA to the voltage level of the PA's power supply. Efficiency is affected by the peak-to-average ratio of the transmitted signal. The envelope tracking modulator maximizes this ratio, correlating the PA's power supply with the envelope of its output signal. Efficient modulators must satisfy certain critical conditions: i) it must be very agile to track the amplitude variations of PA's output voltage; ii) it must reduce the timing mismatch between the PA modulator's supply and PA output waveform envelope to optimize power efficiency and avoid PA saturation, and iii) the envelope tracking modulator must be highly power efficient. This paper reviews several relevant envelope tracking techniques. Hybrid modulators consisting of switching regulators and linear amplifiers have become mainstream envelope tracking systems for wideband applications, in which linear amplifiers complement the functionality of highly efficient but narrow bandwidth switching modulators. Replacements for linear amplifiers include a combination of power-efficient ADC and DACs that provide very agile feedback, increasing the system's slew rate, which allows the modulator to track faster envelope signals. Multi-level switching is another relevant approach utilizing multiple switching voltages to reduce current ripples and enable the use of wider bandwidth switching regulators with high power efficiency. The use of multiple inductors is another interesting approach. Multi-phase switching techniques utilize multiple switching stages in a time-interleaved manner to extend the switching modulator's bandwidth. A slow buck converter can be combined with a fast buck converter and optimized for different switching frequencies; this architecture covers the signal envelope's low- and high-frequency components. The approaches mentioned use switching modulators with analog feedback controllers (Pulse-width modulation [PWM] or hysteretic). However, an alternative approach is prediction-based digital feedforward control. This tutorial discusses all of these approaches.more » « less
-
This work presents a power amplifier (PA) linearization approach based on baseband feedback. The modulated signal envelope is fed back from the transistor's drain to its gate with an applied amplitude and phase shift selected to reduce the intermodulation distortion (IMD3) product at the output. The design targets IMD3 improvement near the PA's 1-dB compression point (P1dB), enabling linear operation at a higher output power level and therefore improved device periphery utilization and efficiency. This approach offers a potential linearization alternative to digital pre-distortion, which cannot be applied in some systems, without affecting the RF performance. The 850-MHz proof-of-concept prototype based on a 15-W GaN device is characterized with a two-tone measurement with 5-MHz spacing, and demonstrates 9-dB improvement of the lower IMD3 tone near the P1dB point.more » « less
-
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.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1109/LMWC.2022.3211162
