1,721,085 research outputs found
Characterization and Modeling of RF GaN Switches Accounting for Trap-Induced Degradation Under Operating Regimes
No full textThis paper describes the performance degradation of RF GaN-on-SiC HEMT switches due to the charge trapping, which is triggered by high voltages under operating regimes. A custom measurement setup is used for the characterization of the switching behavior under dynamic control and blocking voltages. It is shown that both small- [i.e., insertion loss (IL)] and large-signal (LS) performances (i.e., switch compression) are affected by traps. Depending on the applied voltages, an increase of the switch IL up to 50% and significant degradation of the switch compression characteristic were measured for a 4 x 75 μm2 RF switch in 0.25-μm GaN-on-SiC technology. These mechanisms cannot be observed with conventional static characterization, and they are not described by standard RF switch models. A device model capable to account for the observed characteristics is identified and empirically validated under LS conditions at 10 GHz
A GaN HEMT Global Large-Signal Model Including Charge Trapping for Multibias Operation
No full textThis paper presents a novel empirical model for gallium nitride on silicon carbide high-electron mobility transistors. A global state-space formulation describes charge trapping effects by means of suitable 2-D nonlinear lag functions of the applied voltages, extracted from a reduced set of double-pulse current-voltage characteristics. The implementation in CAD tools involves a simple equivalent circuit and lookup tables, making the model well suited for power amplifier design in the presence of signals of practical interest. An extensive validation at both low (4 MHz) and radio frequencies (5.5 GHz) exhibits good accuracy and a robust performance prediction for the operation above the cut-off of dispersive phenomena, across different operating classes and loads, in terms of output power, power-added efficiency, and third-order intermodulation distortion. These results show that traps with both linear and nonlinear dynamics are stimulated in large-signal operation, and that these must be taken into account for global model predictions
Two-Input Nonlinear Dynamic Model Inversion for the Linearization of Envelope-Tracking RF PAs
No full textWe present an algorithm for the real-time inversion of a two-input behavioral model applicable to supply-modulated radio-frequency (RF) power amplifiers (PAs). This approach includes the nonlinear dynamic effects on the RF output due to the mutual interactions between the modulated supply and the RF input. The model inversion consists of an iterative procedure that only relies on the model, which has been empirically identified. It results in an open loop linearization algorithm fully implementable in a digital architecture. The method allows exploiting the trade-off between the power-added efficiency (PAE) and the digital predistortion (DPD) computational load for a given linearity target
Stability Analysis and Design Criteria of Paralleled-Device Power Amplifiers Under Large-Signal Regime
No full textThis paper describes a method for the stability analysis and stabilization criteria in multi-device paralleled power amplifiers (PA) under large-signal operating conditions. The symmetry of the amplifier is exploited for a simple and effective study of odd- and even-order modes. The overall stability analysis is transformed into a sequence of analyses on single-mode single-transistor large-signal equivalent amplifiers, which are carried out by using a conversion matrix approach. Examples of application of the method are provided on a 9-GHz GaAs pHEMT monolithic-microwave integrated-circuit (MMIC) PA and a 590-MHz power silicon bipolar hybrid microwave integrated-circuit (HMIC) PA
A Procedure for GaN HEMT Charge Functions Extraction from Multi-Bias S-Parameters
No full textA charge function identification procedure for GaN-HEMTs is proposed. This is based on a frequency-domain integration of displacement current waveforms obtained from an auxiliary model extracted from multi-bias S-parameters. The method is compared with a similar technique recently proposed, which is instead based on direct acquisitions of large-signal waveforms at the transistor ports by means of a nonlinear vector network analyzer (NVNA). Comparisons between the two approaches are provided by using a 1-mm GaN-on-SiC HEMT, leading to conclude that thermal and trap-induced dispersion on charges have an impact quantified in ∼ 4% - 18% normalized mean square error on the displacement current prediction, depending on the waveforms considered
Dynamic RON Characterization Technique for the Evaluation of Thermal and Off-State Voltage Stress of GaN Switches
Full text linkGaN power switches provide remarkable performance in terms of power-density, reduced parasitics, and high-thermal handling capability that enable the realization of very efficient and compact dc/dc converters. Despite exhibiting state-of-the-art channel conductivity, GaN high electron mobility transistor (HEMT) devices are affected by the degradation of the dynamic on-Resistance (RON) at increasing off-state voltages and operative temperatures. In this paper, a novel laboratory setup and characterization procedure for the dynamic RON of GaN HEMT switches in the presence of thermal- and trapping-effects is presented. The proposed setup allows the study of RON transients after the switching event at variable off-state voltages and temperatures. The use of custom-designed differential amplification stages and a voltage-controlled current source enables the accurate characterization of RON even on large periphery devices. At first, the proposed setup is tested with a well-established and mature device technology such as a Si MOSFET. Degradation of the RON up to 120% due to temperature variation is observed with the presented setup. The setup is then used for the characterization of commercial-grade GaN-on-SiC and GaN-on-Si HEMTs. For both technologies dynamic RON degradations up to 75% and 20% are observed for temperature and off-state voltage variations, respectively. These characterization data are fundamental for the accurate estimation of conduction losses during the design of switching-mode power converters
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
- …
