Ángel Mediavilla Sánchez

Bio: Ángel Mediavilla Sánchez is an academic researcher from University of Cantabria. The author has contributed to research in topics: Antenna (radio) & Intermodulation. The author has an hindex of 9, co-authored 96 publications receiving 345 citations.

Empirical modeling of low-frequency dispersive effects due to traps and thermal phenomena in III-V FET's

Abstract: The modeling of low-frequency dispersive effects due to surface state densities, deep level traps and thermal phenomena plays an important role in the large-signal performance prediction of III-V FET's. This paper describes an empirical modeling approach to accurately predict deviations between static and dynamic drain current characteristics caused by dispersive effects in III-V devices operating at microwave frequencies. It is based on reasonable assumptions and can easily be embedded in nonlinear FET models to be used in Harmonic-Balance tools for circuit analysis and design. Experimental and simulated results, for HEMT's and GaAs MESFET's of different manufacturers, that confirm the validity of the new approach, are presented and discussed together with the characterization procedures required.

Resistive FET mixer conversion loss and IMD optimization by selective drain bias

Abstract: This paper describes a dedicated nonlinear MESFET model, which was used to accurately represent the device's drain-source current nonlinearity. An analytical expression is proposed, based on the Shockley approach, with good derivative reproduction. The evolution of the Ids(Vgs, Vds) Taylor-series-expansion coefficients across V/sub GS/ and V/sub DS/ revealed not only the presence of important minimum conversion loss bias, but also of in-band intermodulation distortion sweet spots that have been used to optimize an FET resistive mixer performance. Some previously reported experimental results are also discussed through the use of the derivatives, and an alternative topology is considered for resistive mixers working on the border between the linear and saturated regions.

Characterizing the gate-to-source nonlinear capacitor role on GaAs FET IMD performance

Abstract: This paper discusses, in a mathematical form and supported by a complete special experimental characterization, the gate-to-source nonlinear capacitor contribution on small-signal intermodulation distortion (IMD) as well as other nonlinear related phenomena such as the onset of phase distortion and gain compression in GaAs FET devices. A simplified one-sided version of our previously proposed test setup and its corresponding characterization formulation are shown to conform a direct technique to extract the second- and third-order coefficients for the Cgs(Vgs) Taylor-series expansion. The extracted terms let us evaluate some of the most widely employed equations for this reactive nonlinearity according to their capability of reproducing its small-signal nonlinear distortion contribution. They are also shown to be responsible for some previously detected differences on IMD behavior at high frequencies and for significant variations on the load selection criteria for high carrier-to-intermodulation ratio and high output-power tradeoffs.

Smoothing the canonical piecewise-linear model: an efficient and derivable large-signal model for MESFET/HEMT transistors

Abstract: In this paper we present the smoothed piecewise-linear (SPWL) model as a useful tool in the device modeling field. The SPWL model is an extension of the well-known canonical piecewise-linear model proposed by Chua, which substitutes the abrupt absolute value function for a smoothing function (the logarithm of hyperbolic cosine), thus providing the model with several interesting properties. In particular, this function makes the model derivable, which is important to predict the intermodulation distortion behavior. Moreover, it allows one to control the smoothness of the global model by means of a single smoothing parameter. The parameters of the model are adapted to fit the nonlinear function, while the smoothing parameter is selected according to derivative constraints. The applied learning algorithm is a second-order gradient method. The proposed SPWL model is successfully applied to model a microwave HEMT transistor under optical illumination using real measurements. The model receives as input the bias voltages of the transistor, the instantaneous voltages, and the optical power and provides the drain to source current. The performance and computational burden of the SPWL model is compared with an empirical model and with some neural networks-based alternatives.

Graphene-Based Ambipolar RF Mixers

Abstract: The combination of the unique properties of graphene with new device concepts and nanotechnology can overcome some of the main limitations of traditional electronics in terms of maximum frequency, linearity, and power dissipation. In this letter, we demonstrate the use of the ambipolar-transport properties of graphene for the fabrication of a new kind of RF mixer device. Due to the symmetrical ambipolar conduction in graphene, graphene-based mixers can effectively suppress odd-order intermodulations and lead to lower spurious emissions in the circuit. The mixer operation was demonstrated at a frequency of 10 MHz using graphene grown by chemical vapor deposition on a Ni film and then transferred to an insulating substrate. The maximum operating frequency was limited by the device geometry and the measurement setup, and a high-quality factor was observed with a third-order intercept point of +13.8 dBm.

A comprehensive explanation of distortion sideband asymmetries

Abstract: This paper presents a comprehensive study of intermodulation-distortion response asymmetries often observed in microwave nonlinear systems subject to a two-tone or multitone test. The reasons for the different amplitudes of the two adjacent tones are first investigated under small- and large-signal regimes, using a general circuit with frequency-dependent embedding impedances and resistive and reactive nonlinearities. It is shown that this intriguing phenomenon can be mainly attributed to the terminating impedances at the baseband or difference frequencies. Multitone behavior is also addressed and its main differences from the two-tone case explained. Those theoretical conclusions are then extrapolated for real circuits and validated by measured results obtained from microwave power amplifiers of two different technologies, i.e., a GaAs MESFET and an Si bipolar junction transistor.

Индикаторы качества светодиодных осветительных систем, применяемых в стоматологической практике для местного освещения операционного поля

Abstract: The currency of the research consists in the necessity if rethinking of the notion of culture in Russian contemporary thought in order to present more adequately the process of development of culture in a future. The paper aims to elucidate political origins of the movement of Proletarian culture that play the leading role in a creation of a new conception of culture. As a materials were used documents and archives, scientific paper of Russian and foreign researchers. As a maim method was used problematicanalytical reconstruction, explored in the framework of an enactive approach that allows to envelop the subject in its evolvement and to concentrate on concrete practical situations of its realization. Such reconstruction permits to accomplish the original interpretation of the problem. The authors focus in the pre-history of the movement. Analyzing the social-political context of the origin of the movement, the authors come to the conclusion about artificially created necessity of political enlightenment of the society by the revolutionaries. The paper demonstrates how agents of proletarian working circles manipulate by the public opinion of working class. As a result, the paper shows the process of formation the ideology of cultural movement revolutionary period and evaluates significance of ideological function in its realization. The authors produce critical evaluation of the history of the movement in original judgment about political grounding of culture.

Wireless Power Transmission: R&D Activities Within Europe

Abstract: Wireless power transmission (WPT) is an emerging technology that is gaining increased visibility in recent years. Efficient WPT circuits, systems and strategies can address a large group of applications spanning from batteryless systems, battery-free sensors, passive RF identification, near-field communications, and many others. WPT is a fundamental enabling technology of the Internet of Things concept, as well as machine-to-machine communications, since it minimizes the use of batteries and eliminates wired power connections. WPT technology brings together RF and dc circuit and system designers with different backgrounds on circuit design, novel materials and applications, and regulatory issues, forming a cross disciplinary team in order to achieve an efficient transmission of power over the air interface. This paper aims to present WPT technology in an integrated way, addressing state-of-the-art and challenges, and to discuss future R&D perspectives summarizing recent activities in Europe.

Prediction of IMD in LDMOS transistor amplifiers using a new large-signal model

Abstract: In this paper, the intermodulation distortion (IMD) behavior of LDMOS transistors is treated. First, an analysis is performed to explain measured IMD characteristics in different classes of operation. It is shown that the turn-on region plays an important role in explaining measured IMD behavior, which may also give a clue to the excellent linearity of LDMOS transistors. Thereafter, with this knowledge, a new empirical large-signal model with improved capability of predicting IMD in LDMOS amplifiers is presented. The model is verified against various measurements at low as well as high frequency in a class-AB power amplifier circuit.