Optimization of Nonlinear Transmission Lines for Harmonic Generation: The Role of the Capacitance-Voltage Characteristic and the Area Effect

In this paper, nonlinear transmission lines (NLTLs) periodically loaded with symmetric voltage dependent capacitances are investigated by means of computer simulation. Specifically, we have studied the role that the C-V characteristic plays on the performance of NLTLs as frequency multipliers. The main conclusion of the work is that the area under the C(V) curve is a key parameter for the optimization of conversion efficiency. This result is interpreted on the basis of soliton like propagation in NLTLs.     

Structural Test Approach for Embedded Analog Circuits Based on a Built-in Current Sensor

This paper presents a test method based on the analysis of the dynamic power supply current, both quiescent and transient, of the circuit under test. In an off-chip measurement, the global interconnect impedance associated with the chip package and the test equipment and, also, the chip input/output cells will complicate the extraction of the information provided by the current waveform of the circuit under test. Thus, the supply current is measured on-chip by a built-in current sensor integrated in the die itself. To avoid the effective reduction of the voltage supply, the measurement is performed in parallel by replicating the current that flows through selected branches of the analog circuit. With the aim of reducing the test equipment requirements, the built-in current sensor output generates digital level pulses whose width is related to the amplitude and duration of the circuit current transients. In this way the defective circuit is exposed by comparing the digital signature of the circuit under test with the expected one for the fault-free circuit. A fault evaluation has been carried out to check the efficiency of the proposed test method. It uses a fault model that considers catastrophic and parametric faults at transistor level. Two benchmark circuits have been fabricated to experimentally verify the defect detection by the built-in current sensor. One is an operational amplifier; the other is a structure of switched current cells that belongs to an analog-to-digital converter.     

Heteroatom Effect on Star‐Shaped Hole‐Transporting Materials for Perovskite Solar Cells

Three new star‐shaped hole‐transporting materials (HTMs) incorporating benzotripyrrole, benzotrifuran, and benzotriselenophene central cores endowed with three‐armed triphenylamine moieties ( BTP‐1 , BTF‐1 , and BTSe‐1 , respectively) are designed, synthesized, and implemented in perovskite solar cells (PSCs). The impact that the heteroatom‐containing central scaffold has on the electrochemical and photophysical properties, as well as on the photovoltaic performance, is systematically investigated and compared with their sulfur‐rich analogue ( BTT‐3 ). The new HTMs exhibit suitable highest‐occupied molecular orbitals (HOMO) levels regarding the valence band of the perovskite, which ensure efficient hole extraction at the perovskite/HTM interface. The molecular structures of BTF‐1 , BTT‐3 , and BTSe‐1 are fully elucidated by single‐crystal X‐ray crystallography as toluene solvates. The optimized (FAPbI₃)_0.85(MAPbBr₃)_0.15‐based perovskite solar cells employing the tailor‐made, chalcogenide‐based HTMs exhibit remarkable power conversion efficiencies up to 18.5%, which are comparable to the devices based on the benchmark spiro‐OMeTAD. PSCs with BTP‐1 exhibit a more limited power conversion efficiency of 15.5%, with noticeable hysteresis. This systematic study indicates that chalcogenide‐based derivatives are promising HTM candidates to compete efficiently with spiro‐OMeTAD.     

Urban data and urban design: A data mining approach to architecture education

The configuration of urban projects using Information and Communication Technologies is an essential aspect in the education of future architects. Students must know the technologies that will facilitate their academic and professional development, as well as anticipating the needs of the citizens and the requirements of their designs. In this paper, a data mining approach was used to outline the strategic requirements for an urban design project in an architecture course using a Project-Based Learning strategy. Informal data related to an award-winning public space (Gillett Square in London, UK) was retrieved from two social networks (Flickr and Twitter), and from its official website. The analysis focused on semantic, temporal and spatial patterns, aspects generally overlooked in traditional approaches. Text-mining techniques were used to relate semantic and temporal data, focusing on seasonal and weekly (work-leisure) cycles, and the geographic patterns were extracted both from geotagged pictures and by geocoding user locations. The results showed that it is possible to obtain and extract valuable data and information in order to determine the different uses and architectural requirements of an urban space, but such data and information can be challenging to retrieve, structure, analyze and visualize. The main goal of the paper is to outline a strategy and present a visualization of the results, in a way designed to be attractive and informative for both students and professionals – even without a technical background – so the conducted analysis may be reproducible in other urban data contexts.     

Road extraction from aerial images using a region competition algorithm.

In this paper, we present a user-guided method based on the region competition algorithm to extract roads, and therefore we also provide some clues concerning the placement of the points required by the algorithm. The initial points are analyzed in order to find out whether it is necessary to add more initial points, and this process will be based on image information. Not only is the algorithm able to obtain the road centerline, but it also recovers the road sides. An initial simple model is deformed by using region growing techniques to obtain a rough road approximation. This model will be refined by region competition. The result of this approach is that it delivers the simplest output vector information, fully recovering the road details as they are on the image, without performing any kind of symbolization. Therefore, we tried to refine a general road model by using a reliable method to detect transitions between regions. This method is proposed in order to obtain information for feeding large-scale Geographic Information System.     

An energy efficient middleware for an ad-hoc AAL wireless sensor network

DIA (Dispositivo Inteligente de Alarma, in Spanish) is an AAL (Ambient Assisted Living) system that allows to infer a potential dangerous action of an elderly person living alone at home. This inference is obtained by a specific sensorisation with sensor nodes (portables and fixes) and a reasoning layer embedded in a PC that learns of the users behaviour patterns and advices when actual one differs significantly of the normal patterns. In AAL systems, energy is a limited resource therefore sensor devices need to be properly managed to conserve energy. In this paper, we introduce the design and implementation of innovative and specific mechanisms at the sensory layer middleware which is capable of, first to discriminate spurious motion detections assuming that these signals do not resemble the patterns of real motion detections and, second to reduce the dynamics of messages by a sensor signal processing in order to compress the whole information in one single event. The middleware achieves power saving by modifying the raw information from sensors and adapting it to the predefined semantic of the reasoning layer. It manages the important task of data processing from sensors (raw information), and transfers the pre-processed information into the top layer of reasoning in a more energy efficient way. We also address the trade-off between reducing power consumption and reducing delay for incoming data. We present results from experiments using our implementation of these mechanisms at the middleware that comprises from node firmware to the PC driver. The number of messages of the proposed method with respect to the raw data is reduced by approximately 98.5%. The resources used in the PIR signal processing is reduced by approximately 85%. The resulting delay introduced is small (10–19 s) but system dynamics is slow enough to avoid contextualisation errors or reduction of system performance. We consider these results as very satisfactory.     

An 8-Bit Digitally Controlled Programmable Phase Shifter Circuit for Sinusoidal Signals with 252∘ Phase Control Range

In this paper, the synthesis, design, and implementation of a programmable phase shifter circuit for sinusoidal signals is presented. The proposed circuit, built-up herein with operational amplifiers (OPAMPs), high precision resistors and low voltage switches, consists of a digitally controlled amplitude attenuator in combination with a single-tone orthogonalizer. Experimental results agree with theoretical background: the attained phase range was 252^° in 256 steps with a median step of 0.9^°. The inaccuracy of the circuit was determined to be of 0.03 %. Contrary to other OPAMP approaches for sinusoidal signals reported in the literature and based on a first-order all-pass filter structure, the approximation suggested in this work is based on a different concept. The achieved results demonstrate the functionality of the system for the case of a sinusoidal signal with frequency of 1 kHz. Notwithstanding, the proposed architecture can be extended to operate at higher frequencies by using different building blocks with larger bandwidth. Furthermore, it can be extended as well to work out with other periodic input waveforms, like triangular shapes or square waves, with the use of an appropriate orthogonalizer.     

Socially-Aware Multimedia Dissemination in Personal Mobile Networks

Wireless Personal Communications - Mobile multimedia entertainment is pervasive on mobile devices, leading people to access, store and disseminate a diversity of multimedia contents anytime and...     

Dynamic modeling of tunable analog integrated filters for a stability study of on-chip automatic tuning loops

Continuous-time filters with automatic tuning loops are nonlinear feedback systems that are potentially unstable. To ensure stability, particularly if the design of the loop controllers is to be improved, the appropriate linear dynamic modeling of the tunable filter, including control inputs, should be attained. This work aims to present a general dynamic modeling of continuous-time analog filters with automatic tuning capability. The general analysis leads to an equivalent small-signal linearized incremental model, from which transfer functions between output variables and control voltages are obtained. Subsequent to the analysis, it is possible to design compensated loops with enhanced stability and dynamic performance. By way of example, the modeling of a particular band-pass CMOS continuous-time analog filter is presented in this paper. Two transfer functions are derived: the transfer function between the output phase shift and the central frequency control voltage, and that between the output amplitude and the quality factor control voltage. These functions are required to properly tune the central frequency and quality factor parameters. This modeling makes it possible to propose an adaptive controller with improved stability and a possible implementation for such a controller. Finally, experimental results are shown for a CMOS 0.8 μm technology.