Advanced High Efficiency Architectures for Next Generation Wireless Communications

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Watt-Level Ka-Band Integrated Doherty Power Amplifiers: Technologies and Power Combination Strategies Invited Paper

This paper discusses some of the design choices underlying the development of watt-level integrated Doherty power amplifiers in the K and Ka band, focusing on compound semiconductor technologies. The key aspect of on-chip power combination is discussed, presenting and comparing some of the possible alternatives. Then, the impact on the achievable bandwidth and performance of different parameters is quantified, adopting an approximate analysis, which focuses on the Doherty output combiner and allows estimating the non-linear performance of the amplifier thanks to some simplifying assumptions, without requiring a full, non-linear model of the active devices. Two sample GaAs and GaN technologies are compared first, considering parameters that are representative of the currently available commercial processes, and then several power combination strategies are analyzed, adopting the GaN technology, which is currently the only one that allows achieving the power levels required by the applications directly on chip. Finally, some hints as to the impact of the output parasitic effects of the transistors on the presented analysis are given

Ka-band MMIC GaN Doherty Power Amplifiers: Considerations on Technologies and Architectures

This paper presents a comparison of two sample GaN technologies, one on Silicon and the other on Silicon Carbide substrate, when applied to the design of an integrated Doherty power amplifier. Two different target applications are considered, namely the satellite Ka-band downlink (17.3-20.3 GHz) and terrestrial communications in the n257 FR2 5G band (26.5-29.5 GHz), with different specifications but similar absolute frequency ranges. Considerations are made highlighting the advantages and disadvantages of the two technologies for the design of high-frequency MMIC Doherty Power Amplifiers in the presented scenarios

Generalized Symmetrical 3 dB Power Dividers with Complex Termination Impedances

The paper introduces a class of two-way, 3 dB narrowband power dividers (combiners), closed on complex termination impedances, that generalizes a number of topologies presented during past years as extensions of the traditional Wilkinson design. Adopting even-odd mode analysis, we demonstrate that, under very broad assumptions, any axially symmetric reactive 3-port can be designed to operate as a 3 dB two-way power divider, by connecting a properly designed isolation impedance across two symmetrically but arbitrarily located additional ports. We show that this isolation element can be evaluated by a single input impedance or admittance CAD simulation or measurement; moreover, an explicit expression is given for the isolation impedance. The theory is shown to lead to the same design as for already presented generalizations of the Wilkinson divider; further validation is provided through both simulated and experimental case studies, and an application of the theory to the design of broadband or multi-band couplers is suggested

Efficiency versus linearity trade-off in an S-band class-AB power amplifier

This paper presents a design strategy to simultaneously optimize the efficiency and linearity of a single-device class-AB power amplifier, given minimum output power and gain requirements. The adopted linearity metric is the highest inter-modulation distortion in a two-tone test with 20MHz spacing. The simultaneous selection of optimum source and load terminations that provide the best trade-off among all of the requirements is described in detail, and the synthesis of the matching networks is then presented. A prototype is developed based on a 6W packaged GaN device around 3.5 GHz, manufactured and measured. According to the measured results, the amplifier achieves output power higher than 38dBm with associated gain higher than 12 dB and saturated power-added efficiency in excess of 73% in a single-tone test at 3.25 GHz, while providing a 33% power-added efficiency and -30 dBc inter-modulation distortion in the 20MHz two-tone test

Assessment of the Performance of Inverse Class-F Power Amplifiers in a Discrete Doherty Architecture

This work presents an assessment, at simulation and experimental levels, of the performance of inverse class-F power amplifiers in a Doherty architecture. Two connectorized amplifier modules, designed for standalone operation, are adopted to construct a quasi-balanced Doherty architecture exploiting 3-dB 90° hybrid couplers at the input and output to demonstrate the concept. The Doherty architecture shows competitive performance at 1.8 GHz, with 43 dBm output power and around 60% efficiency from saturation to 6 dB output power back-off. The performance is in line with the state of the art of integrated load-modulated amplifiers, demonstrating the validity of the approach

Proliferative senescence in hematopoietic stem cells during ex-vivo expansion.

The good outcome of hematopoietic stem cell (HSC) transplantation is hampered by low doses of CD34+ cell infusion. Transplanted HSCs undergo a replicative stress that causes accelerated senescence due to rapid telomere shortening. The expansion of human cord blood HSCs is instrumental in obtaining a large number of "good quality" cells, in terms of telomere length and telomerase activity compared to adult HSCs

Continuous Inverse Class-F GaN Power Amplifier with 70% Efficiency over 1.4-2 GHz Bandwidth

This work presents the design and experimental characterization of a wideband continuous inverse class-F power amplifier, covering several bands in the 5G FR1 frequency range, and thus suitable for base station applications. The design spaces of the class-F and inverse class-F in terms of input and output terminations are reviewed and compared, and the design choices relative to an implementation using a packaged device are described. Measurements show a saturated output power of 40 dBm, with corresponding efficiency and gain higher than 70% and 13 dB, respectively, over 1.4-2 GHz. The performance is well in line with the state of the art and is accurately predicted by simulations, proving the effectiveness of the design strategy

Electro-magnetic Crosstalk Effects in a Millimeter-wave MMIC Stacked Cell

This work discusses the design of a 2-stacked cell at 36 GHz, analyzing the large discrepancies found between circuit-level and electro-magnetic (EM) simulations due to crosstalk (gate power leakage). At millimeter-wave frequencies, EM optimization of the inter-stage matching is crucial, however, its layout compactness poses several issues on the selection of the EM set-up, thus simulations reliability was put in doubt. To dispel this doubt the cell was fabricated and tested, demonstrating the effectiveness of EM predictions and the actual presence of gate power leakage. This required a deep re-design of the cell, currently on-going, based on a completely different inter-stage matching approach

Compact GaN-based Stacked Cells for 5G Applications at 26 GHz

This work presents the development of two 2-FET stacked cells at 26 GHz in the WIN Semiconductors 150 nm power GaN/SiC technology. Two different compact layouts, based on the same circuit scheme, are designed targeting similar performance in the FR2 5G frequency band. One version favoring distance between components, to relieve electromagnetic cross-talk, and the other favoring instead symmetry. The cells have been conceived as basic building blocks for the development of high-power 5G amplifiers, rather than as stand-alone amplifiers, hence including only input matching and stabilization networks. Based on large-signal simulations on the optimum load, the cells are expected to deliver around 34 dBm with an efficiency higher than 35% at 26 GHz, and a linear gain of 10 dB. The output power performance is maintained from 24.5 GHz to 27.5 GHz, where the saturated efficiency is above 30 % for both cells. The small-signal experimental characterization results are in very good agreement with the simulations, proving the effectiveness of the electromagnetic simulation setup adopted for all the passive structures, despite the challenges posed by the compact layouts