69,140 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)
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
GaN MMICs for microwave backhaul: Doherty vs. combined class-AB power amplifier
No full textThe Doherty power amplifier is competing with class-AB amplifiers in mobile base-stations, thanks to its superior performances in terms of back-off efficiency. However, in case of microwave backhaul applications, where higher center frequencies and wider bandwidths are needed, it is still not clear if the linearity-efficiency trade-off is in favour of the DPA or of the classical class-AB. In this work, this point is treated reporting the design and experimental characterization of two GaN MMIC power amplifiers for microwave radio links: a combined class-AB and a Doherty amplifier fabricated with same technology and total active device periphery. The modules have been characterized from 6.6 GHz to 7.3 GHz under large signal condition. The obtained results show that the Doherty amplifier can have a beneficial effect on the energy optimization of the system at the expense of larger chip area with respect to the class-AB. Both circuits achieve 40dBm saturated output power, but at 6dB back-off the Doherty shows an efficiency improvement of about 50%. The amplitude and phase distortions of the two PAs have also been measured, and a system level evaluation is provided highlighting pros and cons of each architecture in terms of linearity
Beyond Groundwater: Calibration and Uncertainty Analysis for Large Transient Coupled Models
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