6,763 research outputs found
K-band combined GaAs monolithic Doherty power amplifier
No full textThis paper presents the design, simulations, and measurements of a 35 dBm K-band Doherty power amplifier, fabricated on 0.15μm GaAs monolithic technology of Qorvo. The power amplifier is based on combining on-chip two Doherty modules with a matching power combiner. To demonstrate the power scaling and gain a better insight into the design, the single Doherty module has been fabricated and characterized as well. The Doherty output matching is designed for maximizing the bandwidth and minimizing the components count, with the output capacitance of the active devices determining the impedance inverter impedance. The combined Doherty shows an output power of 35 dBm at 24 GHz, that is almost exactly 3 dB larger than the single Doherty module power module, and with a 6 dB OBO efficiency of 27%, and a gain of 11.5dB. It compares well with the state of the art, representing the highest power GaAs Doherty at similar frequencies
Helping children think: Gaze aversion and teaching
No full textLooking away from an interlocutor's face during demanding cognitive activity can help adults answer challenging arithmetic and verbal-reasoning questions (Glenberg, Schroeder, & Robertson, 1998). However, such `gaze aversion' (GA) is poorly applied by 5-year-old school children (Doherty-Sneddon, Bruce, Bonner, Longbotham, & Doyle, 2002). In Experiment 1 we trained ten 5-year-old children to use GA while thinking about answers to questions. This trained group performed significantly better on challenging questions compared with 10 controls given no GA training. In Experiment 2 we found significant and monotonic age-related increments in spontaneous use of GA across three cohorts of ten 5-year-old school children (mean ages: 5;02, 5;06 and 5;08). Teaching and encouraging GA during challenging cognitive activity promises to be invaluable in promoting learning, particularly during early primary years
GCM simulations of the Indian Ocean dipole influence on East African rainfall: present and future.
No full textSix coupled GCMs are assessed in terms of their ability to simulate observed characteristics of East African rainfall, the Indian Ocean dipole and their temporal correlation. Model results are then used to analyze the future behaviour of rainfall and the DMI. All models simulate reasonably well the spatial distribution and variability of annual and seasonal rainfall over the 1961–1990 period. Model simulation of observed DMI characteristics is less consistent with observations, however, five models reproduce similar correlations to those observed between the DMI and East African short rains (SON). In the future, there are no clear inter-model patterns of rainfall or DMI behaviour. In this sample of models four (two) out of six simulate modest increases (decreases) in annual rainfall by the 2080s. For SON, three of the six models indicate a trend towards increasingly positive phase of the DMI, two indicate a decrease and one shows no substantial change
A 6W uneven doherty power amplifier in GaN technology
No full textIn this paper the design of a 6W uneven GaN Doherty power amplifier is presented. The Doherty PA is designed to achieve high efficiency for modulated signals with high peak to average power ratio used in modern wireless communication systems. The Doherty amplifier has been designed using two equal sized GaN devices for the Main Class AB and Peaking Class C amplifiers. An uneven power divider is used at the input to deliver more input power to the Peaking amplifier than the Main amplifier. The measured maximum output power of the realised uneven Doherty is 38 dBm with 60% of peak power added efficiency (76% of drain efficiency). The power added (drain) efficiency is higher than 52% (62%) up to 6 dB of back off, or 42% (45%) up to 10 dB of back off
Optimisation of a Doherty power amplifier based on dual-input characterisation
No full textThe success of the Doherty architecture compared to other efficiency enhancement techniques derives mainly from its simple design and full-RF nature, not requiring complex digital signal processing to achieve high back-off efficiency. In this work we propose a design strategy for the optimisation of a Doherty power amplifier to mitigate the typical practical issues of this architecture related to inaccuracy of the non-linear model and of the manufacturing. The approach is based on the experimental characterisation of a dual-input Doherty prototype without input section. This test structure is obtained from a single-input Doherty amplifier, designed only through non-linear simulations, by removing the input section and allowing for separate control of the two RF inputs. From the collected data, approximated functions for the phase shift and power splitting versus frequency are identified to be realizable in hardware with RF networks. Compared to the reference single-input Doherty stage, a significantly improved behavior is registered in terms of output power (up to 2.7 dB), efficiency at saturation and back-off (30 % and 15 % respectively) and power gain (2 dB)
A Highly Linear Wideband Polar Class-E CMOS Digital Doherty Power Amplifier
No full textThis article presents the first application of a digital-intensive intrinsically linear digitally controlled class-E technique in a Doherty configuration. By careful nonlinear segmentation and multiphase RF-clocking along with overdrive-voltage control and automatic duty-cycle correction, it is shown that even the nonlinearities related to Doherty operation can be fully handled by the underlying design such that digital predistorion (DPD) can be, in principle, omitted. The nonlinearity behavior of the whole digital Doherty power amplifier (PA) is analyzed, and closed-form equations are given to predict the AM-AM and AM-phase modulation (PM) curves. In addition, time/phase mismatch between the peak and main branches and the AM and PM signals is accurately compensated. In order to achieve the maximum intrinsic linearity, two separate chips with the same architecture, but different design parameters, are fabricated as the main and peak amplifiers in 40-nm bulk CMOS. To achieve a large RF bandwidth and high passive combiner efficiency, a differential low-loss, wideband Marchand balun-based Doherty power combiner, implemented using reentrant coupled lines with independent second-harmonic control is proposed, and together with the matching network is fabricated on a two-layer PCB. The measured peak/6-dB power backoff P OUT, drain efficiency/power-added efficiency at 2.4 GHz are 17.5 dBm/12.2 dBm, 57%/52% and 36%/25% with VDD main/peak = 0.6 V/0.7 V. Measured results without using DPD show -41-dBc adjacent channel power ratio (ACPR) and -36-dB error vector magnitude (EVM) for a 16-MHz OFDM signal at 2.5 GHz. By using DPD, the measured ACPR and EVM of a 16-MHz/32-MHz OFDM signals are -52 dBc/-48 dBc and -50 dB/-48 dB, respectively.Accepted author manuscriptElectronic
A Millimeter-Wave CMOS Series-Doherty Power Amplifier With Post-Silicon Inter-Stage Passive Validation
No full textThis article presents a wideband series-Doherty power amplifier (SDPA) for millimeter-wave (mm-wave) fifth-generation (5G) applications. It features a compact two-step impedance inverting-based series-Doherty power combiner that provides broadband close-to-perfect power back-off (PBO) efficiency enhancement. The amplitude-to-amplitude (AM-AM)/amplitude-to-phase (AM-PM) performance of the load-modulated Doherty power amplifier for broadband operation is analyzed. We also devise a post-silicon inter-stage passive validation (PSIV) approach to evaluate the mm-wave chip prototype utilizing the embedded voltage root mean square detectors. The proposed SDPA is realized in a 40-nm bulk CMOS, and it delivers 20.4 dBm PSAT with 39.1%/34% PAE at 0-/6-dB PBO. Over a 23.5-30 GHz band, its PAE is >24% at 6-dB PBO. At 27 GHz, applying a '2 GHz 16-quadratic-amplitude modulation (QAM) orthogonal frequency-division multiplexing (OFDM)' signal, the proposed SDPA generates 10.2 dBm average power with 18.9% average PAE. The average error vector magnitude is better than -24.5 dB without digital predistortion for a '400-MHz 64-QAM OFDM' signal while generating an average output power of 8.8 dBm with 15% PAE. The AM-AM/AM-PM of the realized SDPA is investigated by employing a '50-MHz 64-QAM OFDM' signal, validating our analysis and showing that the linearity limitation of DPAs is systematic and predictable. Utilizing the proposed PSIV approach, the frequency response of the input/inter-stage passive circuits is measured, indicating an excellent agreement with 3-D electromagnetic (EM) simulation results.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic
The AB-C Doherty power amplifier. Part II: validation
No full textIn part I, the complete theoretical (and nonlinear) analysis of a Doherty amplifier employing a Class AB bias condition for the Main Amplifier and a Class C one for the Auxiliary device has been presented. In this article, the experimental validation of the proposed theory is presented, describing the step-by-step procedure to be adopted when designing an AB-C Doherty. The amplifier was realized at 2.14 GHz in hybrid form using two (0.5 mu m, 1 mm gate periphery) GaN HEMTs. (c) 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE 19: 307-316, 2009
Evaluating GaN Doherty architectures for 4G Picocells, WiMax and microwave backhaul links
No full textThis paper evaluates the Doherty power amplifier architecture in terms of linearity, efficiency and design solutions. As case study four different prototypes are presented, one for 4G Picocells at 2.1 GHz, one for WiMax applications at 3.5 GHz and two for point-to-point microwave backhaul radiolinks at 7 GHz. Experimental results together with design guidelines are discussed addressing strengths and weaknesses of the Doherty architectur
GaN-MMIC Doherty power amplifier with integrated reconfigurable input network for microwave backhaul applications
No full textA 7 GHz GaN MMIC Doherty power amplifier with reconfigurable input network for backhaul applications, is presented. The reconfigurable solution is conceived to be simply implemented in MMIC technologies. To demonstrate the effectiveness of the strategy, a second Doherty with fixed input network, has been designed for comparison. Both prototypes have been realized adopting a commercial GaN HEMT process and characterized in large signal conditions. The experimental results prove the capability of the proposed solution to overcome the issues related to the inaccuracy of the active device nonlinear models especially for the Class-C bias condition required by the Peak amplifier. At 7 GHz both MMICs exhibit an output power of 40 dBm. However, at 6 dB of output power backoff, the reconfigurable Doherty efficiency is 43%, 10% higher than the one of the DPA with fixed input network
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