Dual-input Doherty Power Amplifier Research Articles

Broadband dual-input doherty power amplifier design based on a simple adaptive power dividing ratio function

Broadband dual-input doherty power amplifier design based on a simple adaptive power dividing ratio function

Load Mismatch Compensation of Doherty Power Amplifier Using Dual-Input and Mode Reconfiguration Techniques

Doherty power amplifier (DPA) has shown great potentials in wireless communication systems. However, the output power and efficiency of a DPA are very susceptible to load mismatch. This paper presents the load mismatch analysis and compensation of coupler-based DPAs leveraging on dual-input and mode reconfiguration techniques. A comprehensive analysis, which takes voltage clipping into consideration, is conducted on a coupler-based dual-input DPA (CBDI-DPA) under load mismatch condition. It is illustrated that the parallel Doherty mode could recover the saturation and back-off drain efficiencies (DEs) for the load mismatch in the left and right half parts of the Smith chart, respectively. And the serial Doherty mode could recover the back-off and saturation DEs for the load mismatch in the left and right half parts of the Smith chart, respectively. As a validation, a CBDI-DPA operating at 2.4 GHz is fabricated and measured in this paper. Under the optimal load impedance condition, the fabricated CBDI-DPA delivers a saturation power of more than 43.5 dBm, a saturation DE of more than 70% and a 6 dB back-off DE of more than 60% in both the parallel and the serial Doherty modes. Meanwhile, the simulation and experimental results demonstrate the proposed method can recover the output power and efficiency of a DPA when the load mismatch is inside the 2:1 VSWR circle.

Analysis and design of dual‐input Doherty power amplifier with enhanced efficiency for broadband application

SummaryThere is a large efficiency degradation between the two efficiency peaks in a broadband Doherty power amplifier (DPA) when the working frequency deviates from the center point. In this paper, dual‐input technique is adopted to improve the conversion efficiency over the dynamic power range in broadband DPAs. The efficiency between the two efficiency peaks in the DPA is enhanced through dynamically control the input power levels of the carrier and peaking power amplifiers (PAs) as well as the phase difference between the two sub‐amplifiers. As a proof of concept, a broadband dual‐input DPA (DI‐DPA) operating over 1.1–2.2 GHz is fabricated and measured in this paper. Experimental results show the fabricated DI‐DPA delivers a saturation output power of 43.5–44.7 dBm with a gain of 9.6–11.5 dB and a drain efficiency of 50.5%–58.6% in the interested frequency band. Meanwhile, a 6 dB back‐off drain efficiency of 40.4%–65.8% is also obtained by the DI‐DPA over 1.1–2.2 GHz.

A System Approach for Efficiency Enhancement and Linearization Technique of Dual-Input Doherty Power Amplifier

In this paper, we propose an efficient system approach to improve the power efficiency of dual-input Doherty power amplifier (DIDPA) with maintaining its linearity level. An auto-tuning process based on a hybrid heuristic search control (HHSC) is applied to optimally define DIDPA configuration by optimizing its free parameters. Digital predistortion (DPD) is then integrated to linearize DIDPA using an optimal reduced-complexity model based on the segmentation approach. An optimal pruning process of the free parameters, based on hill-climbing (HC) heuristics, is proposed to reduce the HHSC complexity in order to refine the optimal DIDPA configuration. The system approach has been approved by experimental results, in different scenarios, using an LTE 20 MHz signal with a PAPR of 8 dB. DPD linearization under optimal DIDPA configuration improved linearity using a low-complex model with only 30 coefficients, which exhibited an error vector magnitude (EVM) of 2.5% and an adjacent channel power ratio (ACPR) of −50 dB at an averaged output power of 34 dBm. By updating the cost function coefficients and pruning the free parameters, DIDPA exhibited an EVM of 3%, an ACPR of −50 dB, and a drain efficiency of 47% at an average output power of 39 dBm.

Automatic Optimization of Input Split and Bias Voltage in Digitally Controlled Dual-Input Doherty RF PAs

Digitally controlled Dual-Input Doherty Power Amplifiers (DIDPAs) are becoming increasingly popular due to the flexible input signal splitting between the main and auxiliary stages. Nevertheless, the presence of many degrees of freedom, e.g., input amplitude split and phase displacement as well as biasing for multiple stages, often involves inefficient trial-and-error procedures to reach a suitable PA performance. This article presents automated parameter setting based on coordinate descent or Bayesian optimizations, demonstrating an improvement in the performance in terms of RF output power and power-added efficiency (PAE) in the presence of broadband-modulated signals, yet maintaining suitable linear behavior for, e.g., communications applications.

Analysis of load mismatch effect compensation in Doherty power amplifier

AbstractThis paper presents a theoretical and experimental analysis of the capabilities of the dual-input Doherty power amplifier (DPA) architecture to mitigate efficiency and output power degradations when used in a mismatched load environment. Following a simplified linear piecewise approach, an analytical demonstration is proposed to derive optimal radio frequency drives applied to the Auxiliary path of the DPA to restore power performances while avoiding large signal voltage clipping of active cells. The proposed analytical study is corroborated with harmonic balance simulated results of a C-band, 20-W GaN DPA prototype. The fabricated dual-input DPA prototype has been measured under 1.5-VSWR mismatch configurations to validate the proposed analysis.

Adaptive Signal Separation for Dual-Input Doherty Power Amplifier

In this article, the generating mechanisms of nonlinear distortion of the dual-input Doherty power amplifier (DIDPA) are discussed, and based on this, an adaptive signal separation algorithm (ASSA) is proposed to improve the nonlinearity of DIDPA. The main idea of the ASSA is to minimize the mismatch between the signal separation functions and the intended operation, which is considered to be the leading cause of nonlinearity in DIDPA. The signal separation functions are used to determine the power ratio and phase difference between the main and the auxiliary amplifier. Moreover, in order to maximize the drain efficiency, an efficiency dictionary which is derived from the static measured results is employed during the ASSA. The performance of the ASSA is validated experimentally on a gallium nitride (GaN)-based DIDPA. The measured results show that with the help of the ASSA, the adjacent channel power ratio and normalized mean square error of output signal can be improved significantly without sacrificing efficiency. In order to further demonstrate the validity of the ASSA, the digital predistortion results of the DIDPAs with and without ASSA are compared with two kinds of behavioral models and two kinds of modulation signals.

Digital Dual-Input Doherty Configuration for Ultrawideband Application

In this article, based on a dual-input configuration (DIC), a method for implementing ultrawideband or multiband load-modulated Doherty power amplifiers (DPAs) is proposed. The proposed DIC possesses two Doherty operating modes with respect to the working frequency. Each subamplifier of the DIC plays a changeable role versus frequency, changing from carrier to peaking or changing from peaking to carrier. A dual-input DPA working over 0.7–3 GHz (a relative bandwidth of 124%) is constructed for validating the proposed theory. Under continuous-wave signal excitation, experimental results illustrate that the fabricated power amplifier achieves a 6-dB back-off efficiency of over 40% across 0.7–3 GHz. The maximum output power of the fabricated DPA changes from 42.2 to 44.7 dBm across the whole working band. Meanwhile, a 20-MHz wideband modulated signal with a peak-to-average ratio of 6.04 dB is utilized to stimulate the fabricated DPA at 0.9, 1.8, 2.4, and 2.8 GHz. After digital predistortion, the measured adjacent channel leakage ratios are less than $-$ 50 dBc at four experimental frequency points.

Accelerated Design Methodology for Dual-Input Doherty Power Amplifiers

A novel design theory and the methodology are presented for dual-input Doherty power amplifiers (DPAs) in which the auxiliary transistor does not fully turn off at backoff power. Given the input parameters selected by the PA designer, a Doherty load modulation behavior is exactly implemented at the current-source reference planes of the transistors by solving for the characteristic impedance of the Doherty quarter-wave transformer and the common load. The Doherty output combiner at the package reference plane that sustains the desired dual-input DPA performance is then synthesized using nonlinear embedding and exactly implemented with a lossless and reciprocal circuit. The new analytic DPA design theory also provides an expanded design space, which facilitates the selection of the optimal design based on the gain, linearity, and efficiency tradeoff. The design methodology is implemented in a software program to enable the automatic design of a dual-input DPA prototype at the package reference planes within 24 s. To validate the theory and the design methodology, a 2-GHz dual-input asymmetric DPA is fabricated and measured. When excited with a 20-MHz local thermal equilibrium (LTE) signal with 9.55-dB peak-to-average power ratio (PAPR), the DPA achieves an average power-added efficiency (PAE) of 51.6% with an adjacent-channel-power-leakage ratio (ACLR) of −47.1 dBc after linearization.

RF/DSP Codesign Methodology of Enhanced Doherty Amplifiers

In this brief, a mixed radio frequency/digital signal processing (DSP) codesign approach is proposed to enhance the performance of Doherty power amplifiers (PAs). For the hardware optimization, a load-pull-based design methodology is proposed to determine the optimal matching elements of the main amplifier for enhanced efficiency at back-off. Subsequently, DSP control of the baseband input signal is used to efficiently distribute the drive power between the main and auxiliary amplifiers in order to enhance the efficiency at high power levels and also to improve the linearity. Precisely, the input power is evenly distributed between the two amplifiers at the back-off region and then unequally split with more drive into the auxiliary amplifier once the latter turns on. This allows for improving the load modulation behavior of the Doherty PA and flattening its gain response, which yield enhanced efficiency and improved linearity. For the experimental validation, the proposed codesign approach is applied to implement a dual-input Doherty PA based on a 10-W gallium nitride (GaN) device. Measurement results with wideband code division multiple access demonstrated improvements of up to 5% in average drain efficiency and up to 3 dB in adjacent channel leakage ratio.

A Dual-Input Digitally Driven Doherty Amplifier Architecture for Performance Enhancement of Doherty Transmitters

In this paper, the novel architecture of a dual-input and digitally driven Doherty amplifier is proposed with the aim of improving the performance of gallium-nitride (GaN) Doherty transmitters. In this work, the power efficiency is enhanced by using digital adaptive phase alignment to compensate for performance degradation due to bias and power-dependant phase misalignment between the carrier and peaking branches. For experimental validation, the proposed dual-input digital Doherty power amplifier (PA) was implemented using a 10-W GaN transistor. Measurement results demonstrate that the dual-input Doherty prototype exhibited a power-added efficiency (PAE) higher than 50% over an 8-dB output power back-off (OPBO) range. In comparison with the conventional fully analog Doherty PA, this represents a 10% improvement in PAE over the same OPBO range. Using a one-carrier Worldwide Interoperability for Microwave Access signal with a 7-dB peak-to-average power ratio, the dual-input Doherty PA, with digital adaptive phase alignment applied at the input of its peaking path, achieved a PAE of 57% at an average output power of 37.8 dBm, along with a - 22-dBc adjacent channel power ratio (ACPR). This corresponds to an improvement of 7% in PAE and 1 dB in average output power for the same ACPR level in comparison with a conventional fully analog Doherty PA.