Modelo compacto con capacidad de predicción de parámetros físicos para amplificadores de RF

En el presente trabajo se ha presentado un análisis de transistores de efecto de campo usando fuentes de voltaje pulsadas. Se han realizado medidas de microondas en dispositivos de tecnología HEMT’s y LDMOS poniendo en evidencia la diferencia entre el comportamiento estático y dinámico de dichos dispositivos. En base a las medidas se ha realizado un procesamiento de datos derivando una nueva ecuación con la capacidad de reproducir ambos tipos de comportamiento con elevada precisión y en diferentes puntos de operación. Consecuentemente el trabajo aporta un nuevo modelo basado en un circuito no lineal de cuatro terminales. La relevancia de este modelo es la capacidad de predecir los efectos físicos como la dispersión frecuencial y la movilidad electrónica del dispositivo semiconductor. Esto es importante pues la dispersión frecuencial es uno de los problemas más importantes de los sistemas de comunicación modernos que genera efectos memoria limitando la capacidad de transmitir señales de gran ancho de banda. El hecho de poder predecir la movilidad electrónica y la dispersión frecuencial ayudan al diseñador de circuitos a mejorar su calidad y tiempo de diseño. Además, permite a la industria de fabricación de componentes de RF ahorrar costos de producción pues esta técnica permite predecir el comportamiento de los circuitos antes de implementarlos. La metodología para la obtención del modelo compacto ha sido validada a través de la implementación de un amplificador de potencia en tecnología LDMOS usando la técnica propuesta. El modelo propuesto es abierto puesto que la nueva técnica propuesta se puede implementar en cualquiera de los modelos convencionales usados actualmente en el ámbito industrial y académico.In this work presents an analysis of field effect transistors using pulsed voltage sources has been presented. Microwave measurements have been made in HEMT's and LDMOS technology devices highlighting the difference between the static and dynamic behavior of these devices. Based on measurements, data processing has been performed, deriving a new equation with the ability to produce both types of behavior with high precision and at different points of operation. Consequently, the work provides a new model based on a non-linear four-terminal circuit. The relevance of this model is the ability to predict physical effects such as frequency dispersion and electronic mobility of the semiconductor device. This is important because the frequency dispersion is one of the most important problems of modern communication systems that generates memory effects limiting the ability to transmit signals of high bandwidth. The fact of being able to predict the electronic mobility and the frequency dispersion help the circuit esigner to improve their quality and design time. It also allows the RF component manufacturing industry to save production costs as this technique allows to predict the behavior of the circuits before implementing them. The presented methodology has been validated through the implementation of a power amplifier in LDMOS technology using the proposed technique. The proposed model is open since the proposed new technique can be implemented in any of the conventional models currently used in the industrial and academic field.Revisión por paresCampus Arequip

The second IEEE MTT-S Latin America Microwave Conference

Extraído de los primer párrafo del artículo: The second edition of the IEEE Microwave Theory and Techniques Society (MTT-S) Latin America Microwave Conference (LAMC) was held in Arequipa, Peru, over the second week of December 2018. It was organized by the MTT-S Peru Chapter in Arequipa, Peru (The first edition of LAMC took place 12–14 December 2016, in Puerto Vallarta, Mexico, and was a great success.) Following official approval in 2015 of LAMC as a biannual MTT-S conference, there were several strategic activities developed in Region 9, such as the creation of new MTT-S Chapters and the organization of several Distinguished Microwave Lecturers (DMLs) visits. Those activities were key to the successful organization of this conference.Revisión por paresCampus Arequip

New methodology for modeling, design and implementation of RF power amplifiers

This work presents a new methodology for modeling, design and implementation of power amplifiers in different technologies. As result of comparison, a flowchart with a new methodology is proposed which can be useful for the designer to design and implement power amplifiers with low, medium and high power devices in different technologies. This paper is divided in 4 parts: The first one is an introduction to the importance of modeling and design techniques in the final implementation of power amplifiers for the modern communication systems. The second one details the modeling process for different technologies, which final result is a unified model. The third part is related with the characterization of high power transistors, with special emphasis on substrate characterization and final implementation of a power amplifier. Finally, in the fourth part, the new methodology is proposed based on the comparisons of previous procedures.Revisión por paresCampus Arequip

Medida de la movilidad electrónica en dispositivos GaAs: dependencia con la polarización y la frecuencia

In this paper we present a new method to evaluate mobility in GaAs devices as well as its dependence on frequency and bias point. Starting from the relationship between the high order derivative of the device drain current source, gmd, and the mobility two alternative measurement methods to obtain this parameter versus both bias conditions and frequency will be presented. At last, the experimental obtained results will show the validity of the presented approach

Cálculo de la movilidad en dispositivos HEMT a partir de medidas de intermodulación

In this paper we present a new method to evaluate mobility in HEMT devices. This new approach is based in the measurement of the high order derivatives of the device drain current source as a means of determining the different parameters of the new proposed mobility equation. The presented results will probe the validity of the approach in both linear and saturation regions

Movilidad respecto al campo eléctrico y la frecuencia en dispositivos MESFET/HEMT

In a previous work the observed differences between the static and dynamic V-I characteristics of MESFETs and HEMTs were attributed to electric field and frequency effects that could be accounted for via the mobility figure for the device. In this paper we continue with this work by exploring in more detail the relationship between the electric field and frequency conditions on the mobility value using a HEMT device. We believe that the original multi-bias mobility measurements described in this paper can be applied equally successfully to the MESFET device

Dependencia de los estados trampa respecto al campo eléctrico en dispositivos MESFET y HEMT

A new measurement procedure for observing the dependence of the frequency dispersion effect on electric field for GaAs MESFET/HEMT devices is presented. The new procedure employs a statistically based pulse I/V measurement system for observing the memory effect in these devices. The results indicate, possibly for the first time, the true extent of the effects of the traps in these devices

Clustering COVID-19 ARDS patients through the first days of ICU admission. An analysis of the CIBERESUCICOVID Cohort

Background Acute respiratory distress syndrome (ARDS) can be classified into sub-phenotypes according to different inflammatory/clinical status. Prognostic enrichment was achieved by grouping patients into hypoinflammatory or hyperinflammatory sub-phenotypes, even though the time of analysis may change the classification according to treatment response or disease evolution. We aimed to evaluate when patients can be clustered in more than 1 group, and how they may change the clustering of patients using data of baseline or day 3, and the prognosis of patients according to their evolution by changing or not the cluster.Methods Multicenter, observational prospective, and retrospective study of patients admitted due to ARDS related to COVID-19 infection in Spain. Patients were grouped according to a clustering mixed-type data algorithm (k-prototypes) using continuous and categorical readily available variables at baseline and day 3.Results Of 6205 patients, 3743 (60%) were included in the study. According to silhouette analysis, patients were grouped in two clusters. At baseline, 1402 (37%) patients were included in cluster 1 and 2341(63%) in cluster 2. On day 3, 1557(42%) patients were included in cluster 1 and 2086 (57%) in cluster 2. The patients included in cluster 2 were older and more frequently hypertensive and had a higher prevalence of shock, organ dysfunction, inflammatory biomarkers, and worst respiratory indexes at both time points. The 90-day mortality was higher in cluster 2 at both clustering processes (43.8% [n = 1025] versus 27.3% [n = 383] at baseline, and 49% [n = 1023] versus 20.6% [n = 321] on day 3). Four hundred and fifty-eight (33%) patients clustered in the first group were clustered in the second group on day 3. In contrast, 638 (27%) patients clustered in the second group were clustered in the first group on day 3.Conclusions During the first days, patients can be clustered into two groups and the process of clustering patients may change as they continue to evolve. This means that despite a vast majority of patients remaining in the same cluster, a minority reaching 33% of patients analyzed may be re-categorized into different clusters based on their progress. Such changes can significantly impact their prognosis

The evolution of the ventilatory ratio is a prognostic factor in mechanically ventilated COVID-19 ARDS patients

Background: Mortality due to COVID-19 is high, especially in patients requiring mechanical ventilation. The purpose of the study is to investigate associations between mortality and variables measured during the first three days of mechanical ventilation in patients with COVID-19 intubated at ICU admission. Methods: Multicenter, observational, cohort study includes consecutive patients with COVID-19 admitted to 44 Spanish ICUs between February 25 and July 31, 2020, who required intubation at ICU admission and mechanical ventilation for more than three days. We collected demographic and clinical data prior to admission; information about clinical evolution at days 1 and 3 of mechanical ventilation; and outcomes. Results: Of the 2,095 patients with COVID-19 admitted to the ICU, 1,118 (53.3%) were intubated at day 1 and remained under mechanical ventilation at day three. From days 1 to 3, PaO2/FiO2 increased from 115.6 [80.0-171.2] to 180.0 [135.4-227.9] mmHg and the ventilatory ratio from 1.73 [1.33-2.25] to 1.96 [1.61-2.40]. In-hospital mortality was 38.7%. A higher increase between ICU admission and day 3 in the ventilatory ratio (OR 1.04 [CI 1.01-1.07], p = 0.030) and creatinine levels (OR 1.05 [CI 1.01-1.09], p = 0.005) and a lower increase in platelet counts (OR 0.96 [CI 0.93-1.00], p = 0.037) were independently associated with a higher risk of death. No association between mortality and the PaO2/FiO2 variation was observed (OR 0.99 [CI 0.95 to 1.02], p = 0.47). Conclusions: Higher ventilatory ratio and its increase at day 3 is associated with mortality in patients with COVID-19 receiving mechanical ventilation at ICU admission. No association was found in the PaO2/FiO2 variation

Global variation in diabetes diagnosis and prevalence based on fasting glucose and hemoglobin A1c

Fasting plasma glucose (FPG) and hemoglobin A1c (HbA1c) are both used to diagnose diabetes, but these measurements can identify different people as having diabetes. We used data from 117 population-based studies and quantified, in different world regions, the prevalence of diagnosed diabetes, and whether those who were previously undiagnosed and detected as having diabetes in survey screening, had elevated FPG, HbA1c or both. We developed prediction equations for estimating the probability that a person without previously diagnosed diabetes, and at a specific level of FPG, had elevated HbA1c, and vice versa. The age-standardized proportion of diabetes that was previously undiagnosed and detected in survey screening ranged from 30% in the high-income western region to 66% in south Asia. Among those with screen-detected diabetes with either test, the age-standardized proportion who had elevated levels of both FPG and HbA1c was 29-39% across regions; the remainder had discordant elevation of FPG or HbA1c. In most low- and middle-income regions, isolated elevated HbA1c was more common than isolated elevated FPG. In these regions, the use of FPG alone may delay diabetes diagnosis and underestimate diabetes prevalence. Our prediction equations help allocate finite resources for measuring HbA1c to reduce the global shortfall in diabetes diagnosis and surveillance