Eva Vidal

Synchronization of nonlinear electronic oscillators for neural computation

This paper deals with coupled oscillators as the building blocks of a bioinspired computing paradigm and their implementation. In order to accomplish the low-power and fast-processing requirements of autonomous applications, we study the microelectronic analog implementation of physical oscillators, instead of the software computer-simulated implementation. With this aim, the original oscillator has been adapted to a suitable microelectronic form. So as to study the hardware nonlinear oscillators, we propose two macro models, demonstrating that they preserve the synchronization properties. Secondary effects such as mismatch and output delay and their relation to network synchronization are analyzed and discussed. We show the correct operation of the proposed electronic oscillators with simulations and experimental results from a manufactured integrated test circuit. The proposed architecture is intended to perform the scene segmentation stage of an autonomous focal-plane self-contained visual processing system for artificial vision applications.

Current-mode BiCMOS sliding-mode controller circuit for AC signal generation in switching power DC-DC converters

This communication describes the design of a microelectronic BiCMOS analog circuit, intended to be applied to the sliding-mode control of switching DC-DC power converters for the application of generating a sinusoidal signal with externally adjustable amplitude, frequency and offset. The circuit implements a sliding law over a nonlinear autonomous switching surface. The proposal of this analog design, which operates in current-mode, represents good performance as long as operation speed, power consumption, suitability for low voltage operation and interference robustness are concerned. The main circuit is composed of externally linearized transconductors based on current conveyors, current-mode full-wave rectifiers and transimpedance high-speed comparators, as well as bipolar translinear squaring cells. HSPICE transistor-level simulations for a BiCMOS 1.2 /spl mu/m technology validate the functionality of the proposed sliding-mode controller implementation.

Nonlinear analytical model of the MRC (MOS resistive circuit)

We analyze the significant departures between the predicted behavior and the actual performance of MOS Resistive Circuit cells (MRC) due to mobility degradation. These effects are mainly a difference in the value of the resistance implemented, and a nonlinear behavior. A model including these effects is proposed and shown to work through an example.

A complete OTA frequency model

A complete model for the Operational Transconductance Amplifier (OTA) is presented. The model includes the transconductance frequency response, the input bias current to output current transfer function, as well as the dependence of both input and output impedances on input bias current. This model is suitable for being included in complex simulation macromodels or for use in analytical calculations. Simulation results and comparisons are also presented.

A methodology to introduce sustainability into the final year project to foster sustainable engineering projects

The introduction of sustainability skills into higher education curricula is a natural effect of the increasing importance of sustainability in our daily lives. Topics like green computing, sustainable design or environmental engineering have become part of the knowledge required by todays engineers. Furthermore, we strongly believe that the introduction of this skill will eventually enable future engineers to develop sustainable products, services and projects. The Final Year Project is the last academic stage facing students and a step towards their future professional engineering projects. As such, it constitutes a rehearsal for their professional future and an ideal opportunity for reflecting on whether their Final Year Project is sustainable or not, and to what extent. It also provides a good tool for reviewing the lessons learned about sustainability during the degree course and for applying them in a holistic and integrated way. In this paper, we present a guide that allows both students and advisors to think carefully about the sustainability of engineering projects, in particular the Final Year Project.

Design and implementation of an MRC-C TQE filter with on-chip automatic tuning

This work describes the design and implementation of the tuning loops (both central frequency and quality factor control loops) for a bandpass continuous-time fully-balanced filter based on a modification of the Transimpedance Q-Enhancement (TQE) structure, intended for audio-band applications. The circuit has been designed and fabricated in a CMOS 0.8 /spl mu/m technology, and MRC (MOS Resistive Circuit) cells have been used to implement electronically tunable active resistors. Both post-layout transistor-level simulation results and experimental results validate the functionality of the tuning system.

D-MRC: digitally programmable MOS resistive circuit

This paper presents the D-MRC circuit, a mixed-signal cell which operates as a digitally-controlled differential resistor, and that is suited to programmable continuous-time MOSFET-C filter applications. The cell is based on a digitally-controlled extension of the MRC (MOS Resistive Circuit) cell, in which digital tunability is obtained by embedding in the same MRC transistors both the triode-region and switch functions, providing a compact implementation that preserves circuit performance. This cell is of interest for static and dynamic reconfigurability of mixed-signal circuits, as required in multistandard wireless CMOS receivers. The proposed cell has been designed down to the layout level for a particular prototype with 3-bit digital controllability in 0.8 /spl mu/m CMOS technology. Post-layout simulation results validate the functionality of the proposed cell and its application to a digitally-tunable continuous-time MOSFET-C filter.

Bandwidth-enhancement g m -C filter with independent ω O and Q tuning mechanisms in both topology and control loops

This paper deals with the proposal of a new topology for a gm-C continuous time filter which allows the adjustment and tuning of its characteristic parameters (ωO and Q) in an independent way (without cross-tuning), thereby extending the Q range of the filter for a particular ωO value. Additionally a comparison of three different Q-tuning algorithms is presented. It is shown that an LMS-based Q-control strategy allows to overcome the intrinsic dependence between the Q and ωO tuning loops. The combination of both the proposed filter topology and the selected control loop algorithms results in an enhanced transient performance as well as an improvement in terms of cross-detuning.

Selective similarity function for VLSI analog signal processing

The similarity calculation of two input voltages can be performed in the analog domain by means of a very compact current switch combined with a differential pair stage. Local feedforward of the current switch allows the circuit to work without the need of any external control ensuring at the same time very high selectivity. The current switch is analyzed by means of its large-signal model, since the first-order small-signal model is not enough to obtain insight into its behavior. The obtained peak cell circuit is applied to bioinspired gray-level image segmentation focal-plane processor. Other direct applications of the current switch are full-wave differential rectifiers and two-input maximum/minimum circuits.

Complete nonlinear model for the MRC (MOS resistive circuit)

The most significant sources of nonlinearity in the MOS resistive circuit behaviour are identified and deeply analysed in this contribution. Their influence on the MRC performance and, therefore, in the circuits containing such structure is evidenced through some examples and evaluated. Some reasonable hints about the way to minimise their undesired effects are provided.