105 research outputs found

    Using a Second Order Sigma-Delta Control to Improve the Performance of Metal-Oxide Gas Sensors

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    Controls of surface potential have been proposed to accelerate the time response of MOX gas sensors. These controls use temperature modulations and a feedback loop based on first-order sigma-delta modulators to keep constant the surface potential. Changes in the surrounding gases, therefore, must be compensated by average temperature produced by the control loop, which is the new output signal. The purpose of this paper is to present a second order sigma-delta control of the surface potential for gas sensors. With this new control strategy, it is possible to obtain a second order zero of the quantization noise in the output signal. This provides a less noisy control of the surface potential, while at the same time some undesired effects of first order modulators, such as the presence of plateaus, are avoided. Experiments proving these performance improvements are presented using a gas sensor made of tungsten oxide nanowires. Plateau avoidance and second order noise shaping is shown with ethanol measurements.Postprint (author's final draft

    Circuit modeling of a MEMS varactor including dielectric charging dynamics

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    Electrical models for MEMS varactors including the effect of dielectric charging dynamics are not available in commercial circuit simulators. In this paper a circuit model using lumped ideal elements available in the Cadence libraries and a basic Verilog-A model, has been implemented. The model has been used to simulate the dielectric charging in function of time and its effects over the MEMS capacitance value.Peer ReviewedPostprint (published version

    Pulsed digital oscillators

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    The objective of this paper is to collect the main latest results on pulsed digital oscillators. Rigorous and experimental results are presented that show what kind of sequences are at their output, the relation between these sequences and those of first-order sigma-delta modulators and how is their performance in practical applications. A new variation of the standard topology of PDOs, on which the feedback variable is not position but the velocity of the resonator, is also presented. The first preliminary results obtained with a PDO working with a MEMS cantilever for chemical sensing are presented, which show that it is possible to infer the oscillation frequency directly from the bitstream at the output of the oscillator. Finally, the dependence of the oscillation frequency as a function of the initial conditions of the resonator are also analyzed with simulations.Peer ReviewedPostprint (published version

    Delfos, un recurs interactiu per l'estudi de dispositius electrònics

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    Es presenta un programa interactiu per a un curs bàsic de dispositius semiconductors suportat per ordinador personal. Els destinataris primers són els alumnes de la titulació de segon cicle en Enginyeria Electrònica de la UPC, en particular aquells que la segueixen en format semipresencial. El material presentat s’ajusta al programa d’una de les assignatures del curriculum i al text de referència que s’utilitza. L’objectiu és presentar una col·lecció d’exercicis, prou extensa per cobrir tots els conceptes importants de la matèria, que l’alumne pugui utilitzar per autoavaluar-se, Eventualment, el professor podrà fer servir el mateix recurs per qualificar l’estudiant. El material és d’accés lliure per xarxa.Peer ReviewedPostprint (published version

    Dos qüestionaris interactius d'electrònica: CyDEL i DELFos

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    Es presenten dos qüestionaris interactius d'electrònica: CyDEL, dedicat a l'anàlisi de circuits electrònics bàsics i que dona suport a l'assignatura troncal "CISE 1" d'Enginyeria de Telecomunicació, i DELFOS, per a l'assignatura troncal "DEF 1" d'Enginyeria Electrònica que tracta de l'estudi de dispositius electrònics i fotònics. Un qüestionari interactiu és un programa informàtic que s'executa sobre un ordinador personal i que conté una extensa base de dades d'exercicis d'una determinada matèria. Els qüestionaris admeten fins a quatre diferents modes de treball: a) El mode estudi, pensat per ajudar l'estudiant a aprendre la resolució d'exercicis, per la qual cosa es permet la consulta a pàgines d'ajut i a la solució correcta de l'exercici. b) El mode avaluació, pensat per a que l'estudiant pugui avaluar els coneixements adquirits, es presenta com un examen tipus test amb un full final de correcció que proporciona la nota i el temps dedicat a resoldre'l. c) El mode de resolució de problemes guiats, en el qual l'estudiant pot consultar "pistes" per resoldre cadascun dels apartats i la solució corresponent. d) El mode lectura, que permet a l'estudiant consultar les pàgines d'ajut com si fos un llibre de teoria. En aquest treball es descriuen ambdós qüestionaris i la seva utilització com eina d'aprenentatge

    Digital resonance for MEMS

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    This work shows the application of Pulsed Digital Oscillators to the detection of physical changes in MEMS devices that cause small shifts in their resonance frequencies. Such devices can be used as resonators in several sensor applications. According to this, a case study using a PDO structure to measure small concentrations of volatile organic gas compounds (VOC’s) introduced here. The MEMS devices used are cantilevers with a thin layer of polymer sensitive to the VOC concentration. Such devices have been simulated with the Coventor software to see the influence of the polymer layers on their mechanical responses. Finally, experimental measurements with various VOCs have been done, and results extracted from two PDO system sources, digital and analog, have been analyzed and compared.Peer ReviewedPostprint (published version

    Diffusive representation and sliding mode control of charge trapping in Al2O3MOS capacitors

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    © 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The objective of this paper is to introduce a modeling strategy to characterize the dynamics of the charge trapped in the dielectric of MOS capacitors, using Diffusive Representation. Experimental corroboration is presented with MOS capacitors made of Alumina in three different scenarios. First, the model predictions are compared with the trapped charge evolution due to arbitrary voltage excitation. Second, the predictions are compared with the measurements of a device in which a sigma-delta control of trapped charge is implemented. Finally, the time evolution when the device is simultaneously controlled and irradiated with X-rays is compared with the predictions. In all cases, a good matching between the models and the measurements is obtained.Peer ReviewedPostprint (author's final draft

    Simultaneous control of dielectric charge and device capacitance in electrostatic MEMS

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    This letter presents a double closed loop for simultaneously controlling the net dielectric charge and the device capacitance in contactless electrostatic MEMS devices. The first loop controls the net charge trapped in the dielectric layer by continuously monitoring the horizontal displacement of the C–V characteristic and applying bipolar actuation voltages to keep such net charge at the target value. The second loop adapts the actuation voltages so that the measured capacitance matches a desired value while maintaining the primary control of chargePostprint (author's final draft

    Closed-loop compensation of charge trapping induced by ionizing radiation in MOS capacitors

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    The objective of this work is to explore the capability of a charge trapping control loop to continuously compensate charge induced by ionizing radiation in the dielectric of MOS capacitors. To this effect, two devices made with silicon oxide have been simultaneously irradiated with gamma radiation: one with constant voltage bias, and the other working under a dielectric charge control. The experiment shows substantial charge trapping in the uncontrolled device whereas, at the same time, the control loop is able to compensate the charge induced by gamma radiation in the second device.Peer ReviewedPostprint (author's final draft
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