1,720,966 research outputs found
Evaluation of Trapping Dynamics in GaN HEMTs from Double-Pulse RF Load-Pull Measurements
No full textThis study presents the application of a recently proposed double-pulsed radio-frequency (RF) measurement technique for characterizing the dynamic behavior of Gallium Nitride (GaN) High-Electron-Mobility Transistors (HEMTs). In particular, the measurement procedure aims to analyze the trapping and detrapping mechanisms affecting the device's performance under realistic RF operating conditions. By varying both the RF prepulse duration and the time interval between the RF prepulse and the main RF pulse (ranging from a few microseconds to a few milliseconds), a wide range of trap capture and release dynamics can be evaluated
Modulated-Input Control and Linearization of a Multi-Port Millimeter-Wave PA by VNA-based Calibrated Wideband Measurements
No full textEnhancing K-Band Dual-Input Doherty PA Performance by Bayesian Optimization
Full text linkWe present a methodology based on Bayesian optimization (BO) for the performance enhancement of a dual-input Doherty power amplifier (DIDPA) operating at 24 GHz under wideband modulation. First, we implement a dual-input control (DIC) algorithm, which allows for the user-defined arbitrary nonlinear shaping between the two inputs of the DIDPA. Then, an iterative procedure for the performance optimization is configured, where the tuning variables are the bias voltages and the parameters defining the dual-input shaping. Such a procedure jointly targets the improvement of power-added efficiency (PAE) while maintaining linearity by digital predistortion (DPD). To study the feasibility of the method in terms of convergence time and related tradeoffs in performance, the BO is applied in two fashions, namely, one leveraging a quasistatic model (QSM) of the DIDPA and the other directly on modulated signal acquisitions. The experimental results for high peak-to-average power ratio (PAPR) multitone broadband excitations show that the optimized settings can lead to an absolute improvement of several percentage points in PAE compared to the nonoptimized case, while still maintaining a suitable performance in terms of linearity and output power
A VNA-Based Wideband Measurement System for Large-Signal Characterization of Multiport Circuits
Full text linkThis work reports on a wideband (WB) measurement system based on a vector network analyzer (VNA) topology for multiport large-signal measurements. The setup exploits a modified commercial VNA with WB intermediate frequency (IF) outputs that allow for more than 5-GHz analysis bandwidth (BW), where the IF is captured using an external high-speed oscilloscope. A three-port configuration using six receivers is described, together with the signal processing to achieve the high dynamic range required for WB signal measurements. The calibration procedure to establish reference planes at the three ports of the device-under-test (DUT) is shown. A comparison is made between single-tone continuous-wave (CW) calibration and WB calibration using multitone signals, illustrating advantages, challenges, and limitations. The system is then demonstrated for on-wafer WB characterization and linearization of a dual input Doherty power amplifier (DIDPA) using a 100-MHz instantaneous BW excitation signal at millimeter-wave frequencies. By leveraging on the error-corrected WB waves, an algorithm is proposed for modulated input signal control across a 600-MHz acquisition BW at the DUT on-wafer reference planes. The algorithm enables a user-defined emulated splitting of the input WB signals. The linearization performance of such an emulated PA configuration is finally evaluated
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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