Concurrent Dual-band Power Amplifier Research Articles

A Rapid Matching Network Layout Synthesis and Optimization Method for High-Performance MMIC PAs Using Modified Implicit Space Mapping

In this brief, a new systematic approach of matching network (MN) layout synthesis and optimization for power amplifiers (PAs) is proposed based on implicit space mapping (ISM). Commonly, the performance discrepancy between schematic and initial layout is huge, especially for millimeter wave (mmWave) PAs. To address this issue, the proposed modified ISM can shift the optimization work to the circuit schematic simulations by calibrating carefully-selected auxiliary parameters in the circuit based on EM data. To validate the proposed method, an eligible dual-band inter-stage MN layout is rapidly optimized with only 10 runs of EM-simulations, while a corresponding 16/26.5 GHz concurrent dual-band PA is implemented in a 0.15- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> GaAs pHEMT technology. It exhibits a measured small-signal gain of 21.7/14.1 dB, peak power-added efficiency of 30.2%/40.5%, and saturated output power of 24.8/28.1 dBm with a compact chip size of 2.4 mm2.

Design of a dual-band microwave power amplifier for wireless communications

In this paper, we present a design of a concurrent dual-band power amplifier operating at 5.8 GHz and 9.4 GHz employing a MMIC technology for wireless communications. The active device used is a 0.25 µm AlGaN/GaN HEMT from WIN Semiconductor, Taiwan. The design goal is to achieve the high-efficiency while still retaining other important metrics including output power and power Gain at concurrent dual frequency bands. The performance of the designed amplifier is evaluated at both small and large signal levels through theoretical analyses and simulation using a Keysight ADS simulator. The developed dual-band amplifier delivered a 47% PAE with 30.5 dBm output power and 12.5 Gain at 5.8 GHz, and a 37% PAE with 30.2 dBm output power and 12.2 Gain at 9.4 GHz.

A Digital Predistortion for Concurrent Dual-Band Power Amplifier Linearization Based on Periodically Nonuniform Sampling Theory

In this article, we propose a novel technique of digital predistortion (DPD) for dual-band power amplifiers (PAs) based on the periodically nonuniform sampling (PNS) theory. In contrast to conventional dual-band DPD (2-D-DPD) models, the proposed periodically nonuniform sampled DPD (PNS-DPD) has only a single input, which can largely reduce the model complexity. We fold the two stimuli with aliasing and feed them to a simple single-band DPD model. The desired predistorted signals are reconstructed from aliased DPD output through the PNS theory. Compared with conventional multi-input models that include numerous intermodulation products of the input signals, the complexity of the proposed single-input PNS-DPD model is hugely decreased. The model coefficients of the proposed PNS-DPD can be easily extracted with conventional direct or indirect learning architecture. We experimentally evaluate the proposed DPD on a test bench and compare it with other DPD techniques in the literature. The implementation complexity can be reduced by over 30%, and the identification complexity is also largely reduced.

A High-Efficiency 28 GHz/39 GHz Dual-Band Power Amplifier MMIC for 5G Communication

A high-efficiency 28 GHz/39 GHz concurrent dual-band power amplifier (PA) is proposed using the 90 nm GaAs pseudomorphic high-electron mobility transistor (pHEMT) process for the millimeter-waveband fifth generation (5G) communication application in this letter. Its high efficiency is achieved by adopting a low-loss dual-band output matching network (OMN) and employing a large power push ratio (3:1) for the driver stage and the output stage under the same bias voltage. The dual-band PA has the measured gain of 19.1 and 20.3 dB, as well as the power added efficiency (PAE) of 51.3&#x0025; with the 23.8-dBm output power and 49.5&#x0025; with the 23.7-dBm output power at the 3 dB compression point (<inline-formula> <tex-math notation="LaTeX">$P_{\mathrm {3\,dB}}$ </tex-math></inline-formula>), at 29.6 and 39 GHz, respectively. The area of the proposed dual-band PA is 1.45 mm <inline-formula> <tex-math notation="LaTeX">$\times1.2$ </tex-math></inline-formula> mm including pads.

Modified indirect learning applied to neural network-based pre-distortion of a concurrent dual-band CMOS power amplifier

Current radio communication systems that adopt amplitude and phase modulations demand high linearity and high efficiency. The cascade connection between digital baseband pre-distorter (DPD) and power amplifier (PA) can be a cost-effective solution to guarantee the required linearity without compromising the efficiency. In the design of a DPD for a single band PA, direct learning can be used to extract the pre-inverse parameters or, alternatively, indirect learning can be employed by exchanging the position of the system during the identification procedure to avoid the necessity of a PA model within a closed-loop process. The performance of direct learning is substantially dependent on the accuracy of the behavioral model that replaces the PA. Furthermore, in a practical environment where only an approximation to the inverse is achieved, the linearization capability of the indirect learning is affected by shifting the post-inverse placed after the PA to a pre-inverse located before the PA. For concurrent dual-band PAs, an additional advantage of the indirect approach is that the post-inverse identifications for each band are completely independent of each other. In an authors’ previous work, a comparative analysis between the two learning architectures applied to the linearization of concurrent dual-band PAs was performed based on DPDs modeled by polynomials with memory. This work contributions are the extension of such comparative analysis to DPDs modeled by artificial neural networks, the development of complex-valued three-layer perceptrons suitable for concurrent-dual band DPDs and the introduction of a modified indirect approach to improve the accuracy of previous direct and indirect learnings. Spectre-RF transient simulations are performed in the circuit-under-test described by a wideband 130 nm CMOS PA concurrently stimulated by 2.4 GHz Wi-Fi and 3.5 GHz LTE signals. Reported simulation results show that, in a comparison with the previous direct and indirect learnings with similar output mean powers of about 60 mW, the modified indirect approach provides a superior linearity performance. The modified indirect learning reduces the error vector magnitude (EVM) metric to 0.87% and 1.13% for Wi-Fi and LTE bands, respectively, whereas the indirect and direct learnings achieve EVM equal to or larger than 1.05% and 1.49% for Wi-Fi and LTE bands, respectively.

A 2-D Simplified Memory Polynomial Model for Concurrent Dual-Band Power Amplifiers

A 2-D simplified memory polynomial (2D-SMP) model is proposed for concurrent dual-band power amplifiers (PAs) in this letter. The derivation of the proposed model is similar to that of the 2-D modified memory polynomial (2D-MMP) model. The 2D-SMP model consists of an in-band part and a cross-band modulation part without the envelope factors, which exist in the 2D-MMP model. Theoretical analysis shows that it has moderate complexity but higher modeling accuracy than the 2D-MMP model. The simple least square algorithm can be used to extract the model coefficients, and the additional binary search algorithm for the best envelope factor is not needed. The experimental results show that the 2D-SMP model can achieve higher model accuracy and better digital predistortion (DPD) performance than the 2D-MMP model when a dual-band PA is excited by a combined dual-band long-term evolution signal.

Design of Concurrent Dual-Band Continuous Class-J Mode Doherty Power Amplifier With Precise Impedance Terminations

In this letter, a novel methodology for designing concurrent dual-band continuous class-J mode Doherty power amplifier (DPA) with precise impedance terminations is presented. First, the required impedance condition of the carrier amplifier which operates in continuous class-J mode at the back-off region is analyzed in detail. Based on the proposed theory, the fundamental impedance is realized by taking advantage of the noninfinity output impedance of the peaking stage, then the second harmonic impedance is realized with a harmonic tuning postmatching network. A 1.8-/2.6-GHz dual-band DPA employing commercial GaN devices is designed and implemented to validate the proposed method. The fabricated DPA can achieve 68.5% and 75% drain efficiencies (DEs) for saturated power level at 1.8 and 2.6 GHz, respectively. For the 6-dB back-off region, the measured DEs are 64% and 63% at the two designed frequencies.

A 2-D-Canonical Piecewise Linear Function-Based Behavioral Model for Concurrent Dual-Band Power Amplifiers

A 2-D-canonical piecewise linear (2-D-CPWL) function-based behavioral model is proposed for concurrent dual-band power amplifiers (PAs) in this letter. The model is derived from the Volterra-based 2-D-modified memory polynomial (2-D-MMP) model by replacing the high-order terms with CPWL and it can provide a lower complexity than the 2-D-MMP model and some existing CPWL-based dual-band models. The least-square algorithm can be used to extract the model coefficients. Experimental results show that the proposed 2-D-CPWL model can achieve nearly the same model accuracy and digital predistortion performance compared with the 2-D-MMP model, when a dual-band PA is excited by a combined dual-band long-term evolution signals.

Volterra series-based model for concurrent dual-band power amplifier using dynamic memory depth

In this article, a dynamic dual-band baseband equivalent Volterra (DDBE) model is proposed to compensate the nonlinear distortions of the concurrent dual-band power amplifier (PA). The DDBE model is obtained by improving the discretized dual-band baseband equivalent Volterra model which can describe the output characteristics of concurrent dual-band PA completely in theory but is lack of practicability. Three simplification rules are proposed in the article, and the relevance between in-band intermodulation and in-band cross modulation is employed to simplify the establishment complexity of the model. Then the dynamic kernels are categorized into three groups, and based on this, DDBE models with different level dynamical kernels are derived. In addition, draw on the experience of single-band PA behavioral model, even-order kernels are introduced into DDBE models. Digital predistortion performances of a wideband PA, which works in concurrent dual-band mode, are evaluated to verify the feasibility and advantages of the proposed model.

A methodology for designing class-F−1/J(J−1) high efficiency concurrent dual-band power amplifier

This paper, presents a methodology for designing concurrent dual-band power amplifier (DB-PA) that operates in Class-F−1 at one band and Class-J or Class-J−1 at the other band. It is shown that the second harmonic engineering of Class-F−1 and Class-J or Class-J−1 makes these classes of operation compatible in terms of dual-band realization without introducing higher complexity in realizing the harmonic control network. The design methodology is well illustrated and is validated by implementing a Class F−1/J concurrent dual-band PA operating at 1842 and 2655 MHz bands. Experimental results exhibit output powers of 40 and 41 dBm and efficiencies of 76% and 70% at the lower and upper bands, respectively. The AM-AM, AM-PM and two-tone third-order inter-modulation distortion results imply a good linearity behaviour of the designed PA. Furthermore, the linearity of the designed DB-PA is also verified with a single carrier WCDMA signal, where the PA shows better than −20 dBc adjacent channel power ratio in saturation region at both of the operating bands.

Envelope Preformulation Digital Predistortion for Concurrent Dual-Band Power Amplifiers with Improved Performance and Stability

This letter proposes a novel envelope preformulation digital predistortion technique to linearize concurrent dual-band (DB) power amplifiers (PAs), presenting improved stability/performance, and easier implementation compared to conventional methods. The concurrent DB system was implemented on a GaN Doherty PA by employing two 20-MHz orthogonal frequency division multiplexing signals at the center frequency of 2.25 and 2.45 GHz, respectively. Experimental results have shown great effectiveness of the proposed method, especially when the PA is pushed into highly nonlinear regions, which is very promising for multiband applications in the future communication systems.

An Interband Time-Delay Compensation Algorithm for Concurrent Dual-Band Power Amplifier Characterization

In this letter, an interband time-delay compensation algorithm that is based on correlation enhancement technique has been proposed to process the signals used for concurrent dual-band power amplifier (PA) characterization, where the characterization is a crucial step of behavioral modeling and digital predistortion (DPD) of the PA, and the interband time delay represents the difference of delay time between different channels. Compared with the traditional compensation method which adjusts the trigger or marker delay manually, the proposed method can work online and shows a higher performance. Finally, the modeling and DPD performance of a wideband PA, which works in concurrent dual-band mode, are evaluated to verify the feasibility and advantages of the proposed algorithm.

A Precise Harmonic Control Technique for High Efficiency Concurrent Dual-Band Continuous Class-F Power Amplifier

In this paper, a design approach for a high-efficiency concurrent dual-band power amplifier (PA) with precise harmonic control up to third order is proposed. With the precise harmonic control approach, the high-efficiency performance of the PA can be improved at two arbitrary wide interval frequencies. Based on the inherent impedance matching flexibility of the continuous Class-F (CCF) operating mode, the design spaces of fundamental and harmonic impedances of the PA are largely expanded. The optimal impedances of a CCF PA mode at the internal current-generator (I-gen) plane and package plane are investigated, respectively, and a novel dual-band matching network topology is designed to simultaneously present required load impedances at the fundamental and harmonic impedances of both operation frequencies. First, a harmonic control network is designed to control the harmonic impedances precisely for CCF operation. Then, the fundamental impedances are synthesized using the real frequency technique. To verify the validity of proposed methodology, a dual-band CCF PA operating at 2.6 and 3.5 GHz is designed, fabricated, and measured. The measurement results show that the peak drain efficiency is 76.7% with an output power 42.4 dBm at the lower band and 72.8% with an output power 41.1 dBm at the upper band.

Concurrent dual‐band digital predistortion implemented with reduced look‐up‐tables

A reduced look-up-tables (LUTs) implementation of digital predistortion (DPD) for concurrent dual-band power amplifiers (PAs) is proposed. In the proposed method, the dual-band output is captured jointly with reduced sampling rate, then the PA characteristics of the lower band and the upper band are identified with a group of shared model coefficients, thus DPD can be implemented with shared LUTs for the two bands, which results in reducing the LUTs by 50% comparing with those traditional dual-band DPD techniques implemented with individual LUTs for each band. Experimental results show that the proposed method can achieve better than −48.2 dBc adjacent channel power ration performance with reduced LUTs.

Systematic Crest Factor Reduction and Efficiency Enhancement of Dual-Band Power Amplifier Based Transmitters

A systematic design methodology including novel crest factor reduction (CFR) and power amplifier (PA) efficiency enhancement techniques for concurrent dual-band transmitters is proposed to improve performance under concurrent modulated stimulus, in terms of both efficiency and output power. Conventional energy efficient PAs are typically implemented separately in analog circuit or digital signal domains. However, the proposed method combines a digital domain 2-D power distribution reshaping (2-D-PDR) method to adaptively reshape the signals’ distribution to fit the target PA’s characterization and an analog domain inter-modulation tuning design to enhance the PA’s output capability. Based on the proposed method, an example of concurrent dual-band Doherty PA (DPA) working at 1.9–2.6 GHz LTE bands was designed using two 10-Watt GaN HEMTs. A 2-D-PDR procedure was developed for the designed DPA. The fabricated DPA was measured in concurrent mode under the stimulus of a pair of 10 MHz LTE signals. According to the measured results, the proposed DPA achieved a drain efficiency of 46.6% at an output power of 6.2 W while maintaining a good adjacent channel power ratio and error vector magnitude. To the best of the authors’ acknowledge, this is the state-of-the-art performance for concurrent dual-band PAs. Additionally, measurements are performed on three varied type of PAs using the proposed 2-D-PDR. According to the measured results, about 0.3~0.8 dB power improvement and 1.5%~3% efficiency improvement can be achieved using the proposed 2-D-PDR compared with the conventional 2-D-CFR, proving the feasibility of the proposed technique.

Low-cost FPGA implementation of 2D digital pre-distorter for concurrent dual-band power amplifier

This paper proposes a low-cost hardware architecture based on concurrent dual-band digital pre-distorter (DPD). The architecture is implemented on field programmable gate array (FPGA) to compensate for the nonlinearity of the concurrent dual-band power amplifier (PA). This implementation introduces a novel model complexity reduction technique into system, namely, time-division multiplexing for out-of-band lookup tables (LUTs) sharing. Performances are evaluated with an experimental test setup using a wideband class-F PA. The dual-band signal center frequency separated by 80 MHz. Lower and upper center frequency are located at 2.61 GHz and 2.69 GHz, respectively. This novel DPD implementation maintains excellent performance, but uses hardware resources reduced by 29.17% compared with conventional approaches. The results show that the adjacent channel power ratio (ACPR) is less than 59 dBc and normalized mean square error (NMSE) is around 62dB for lower sideband (LSB) and 63dB for upper sideband (USB).

Digital Predistortion of Single and Concurrent Dual-Band Radio Frequency GaN Amplifiers With Strong Nonlinear Memory Effects

Electrical anomalies due to trapping effects in gallium nitride (GaN) power amplifiers (PAs) give rise to long-term or strong memory effects. We propose novel models based on infinite impulse response fixed pole expansion techniques for the behavioral modeling and digital predistortion of single-input single-output (SISO) and concurrent dual-band GaN PAs. Experimental results show that the proposed models outperform the corresponding finite impulse response (FIR) models by up to 17 dB for the same number of model parameters. For the linearization of a SISO GaN PA, the proposed models give adjacent channel power ratios (ACPRs) that are 7–17 dB lower than the FIR models. For the concurrent dual-band case, the proposed models give ACPRs that are 9–14 dB lower than the FIR models.

Spectra-Folding Feedback Architecture for Concurrent Dual-Band Power Amplifier Predistortion

This paper proposes a spectra-folding feedback (SFFB) architecture for digital predistortion (DPD) of concurrent dual-band power amplifiers (PAs). Conventional dual-band DPD contains a dual-branch feedback path to receive the PA output signals at respective bands. The proposed architecture, however, is constructed by a single-branch receiving path, so that the hardware expense (such as down converters, filters, or analog-to-digital converters) of the feedback path is significantly reduced. In this architecture, simple modifications are made to the down converter to allow the use of only one analog-to-digital converter. With the proposed signal processing in the baseband, the SFFB DPD can achieve comparative performance as the conventional dual-branch DPD. Experiments were performed using various configurations of LTE/LTE-Advanced (long-term evolution/long-term evolution advanced) signals of up to 80 MHz contiguous bandwidth and carrier spacing of 1 GHz. It is clearly shown by the experimental results that the proposed SFFB DPD can achieve satisfactory linearization performance, with significantly reduced hardware complexity.

Low Complexity Coefficient Estimation for Concurrent Dual-Band Digital Predistortion

Dual-band or multi-band RF power amplifiers (PAs) have attracted a lot of attention in recent years as they rise to the challenge of segmented spectrum allocation in wireless systems. Adaptive digital predistortion (DPD) for concurrent dual-band PAs evolves from existing DPD for single-band PAs. In this paper, we derive the baseband dual-band Volterra model from the corresponding passband model. In addition, the computational complexity of the DPD estimation algorithm increases dramatically as the number of coefficients for dual-band DPD is much larger than that for single-band DPD. In this paper, we propose a low complexity DPD coefficient estimation algorithm for concurrent dual-band PAs based on polar decomposition of the general Volterra model. By dividing complex-valued coefficient estimation into amplitude estimation and phase estimation separately, the proposed algorithm achieves at most 75% computational complexity reduction. Moreover, the proposed algorithm can achieve similar performance with the conventional coefficient estimation method. Simulation and measured results validate performance of the proposed algorithm for a solid-state PA.

Comments on “Novel Dual-Band Matching Network for Effective Design of Concurrent Dual-Band Power Amplifiers”

A novel dual-band matching network for concurrent dual-band power amplifiers has been proposed and discussed by Fu in January 2014. The first stage matching network effectively accomplished real-to-complex impedance transformation by utilizing a transmission line, a short-circuited stub and an open-circuited stub. However, the obtainment of the values of the electrical parameters are realized by tuning and observing Smith Chart, no analytical design methodology given. In this comment, rigorous design equations of the real-to-complex matching network are extracted, and two numerical instances are demonstrated for verification. Additionally, an error about the input impedance in original paper is corrected.