Compact low-power calibration mini-DACs for neural arrays with programmable weights

This paper considers the viability of compact low-resolution low-power mini digital-to-analog converters (mini-DACs) for use in large arrays of neural type cells, where programmable weights are required. Transistors are biased in weak inversion in order to yield small currents and low power consumptions, a necessity when building large size arrays. One important drawback of weak inversion operation is poor matching between transistors. The resulting effective precision of a fabricated array of 50 DACs turned out to be 47% (1.1 bits), due to transistor mismatch. However, it is possible to combine them two by two in order to build calibrated DACs, thus compensating for inter-DAC mismatch. It is shown experimentally that the precision can be improved easily by a factor of 10 (4.8% or 4.4 bits), which makes these DACs viable for low-resolution applications such as massive arrays of neural processing circuits. A design methodology is provided, and illustrated through examples, to obtain calibrated mini-DACs of a given target precision. As an example application, we show simulation results of using this technique to calibrate an array of digitally controlled integrate-and-fire neurons.Gobierno de España TIC1999-0446-C02-02, TIC2000-0406-P4-05, FIT-07000/2002/921, TIC2002-10878-EEuropean Union IST- 2001-3412

On turning waves for the inhomogeneous Muskat problem: a computer-assisted proof

We exhibit a family of graphs that develop turning singularities (i.e. their Lipschitz seminorm blows up and they cease to be a graph, passing from the stable to the unstable regime) for the inhomogeneous, two-phase Muskat problem where the permeability is given by a nonnegative step function. We study the influence of different choices of the permeability and different boundary conditions (both at infinity and considering finite/infinite depth) in the development or prevention of singularities for short time. In the general case (inhomogeneous, confined) we prove a bifurcation diagram concerning the appearance or not of singularities when the depth of the medium and the permeabilities change. The proofs are carried out using a combination of classical analysis techniques and computer-assisted verification.Comment: 30 pages, 6 figure

La representación política en España en las Cortes de antiguo y del nuevo Régimen

Memoria leida en el acto de recibir la investidura de doctor en Derecho

La mediación social y Teléfonos de México (aplicación de los modelos de Martín Serrano)

The text intends to apply the canonical models/forms proposed by the book La mediación social, in the specific case of an organization: in this case, the most important telephone company in Mex-ico: TELMEX. The interesting thing is that it offers several approaches of organizational change, showing at the same time the complexity of the cultural and technological processes that took place in an enterprise of more than 40 000 people. It is proved that the effectiveness of the model proposed by Manuel Martín Serrano is not only an epistemological exercise but an instrument for strategic planning as well as political and trade union negotiation.El texto intenta aplicar los modelos/formas canónicas que el libro de La mediación social propone al caso específico de una organización: en este caso la empresa más importante de telefonía de México: TELMEX. Lo interesante es que nos ofrece varias visiones del cambio organizacional que permiten observar la complejidad en la que operaron los cambios tecnológicos y culturales en una empresa de más de 40 mil personas. Se demuestra que la eficacia del modelo propuesto por Manuel Martín Serrano no solo es un ejercicio epistemológico sino un instrumento de planeación estratégica y negociación político sindical

A spatial contrast retina with on-chip calibration for neuromorphic spike-based AER vision systems

We present a 32 32 pixels contrast retina microchip that provides its output as an address event representation (AER) stream. Spatial contrast is computed as the ratio between pixel photocurrent and a local average between neighboring pixels obtained with a diffuser network. This current-based computation produces an important amount of mismatch between neighboring pixels, because the currents can be as low as a few pico-amperes. Consequently, a compact calibration circuitry has been included to trimm each pixel. Measurements show a reduction in mismatch standard deviation from 57% to 6.6% (indoor light). The paper describes the design of the pixel with its spatial contrast computation and calibration sections. About one third of pixel area is used for a 5-bit calibration circuit. Area of pixel is 58 m 56 m, while its current consumption is about 20 nA at 1-kHz event rate. Extensive experimental results are provided for a prototype fabricated in a standard 0.35- m CMOS process.Gobierno de España TIC2003-08164-C03-01, TEC2006-11730-C03-01European Union IST-2001-3412