Transient and Steady-State Analysis of the Affine Combination of Two Adaptive Filters

In this paper, we propose an approach to the transient and steady-state analysis of the affine combination of one fast and one slow adaptive filters. The theoretical models are based on expressions for the excess mean-square error (EMSE) and cross-EMSE of the component filters, which allows their application to different combinations of algorithms, such as least mean-squares (LMS), normalized LMS (NLMS), and constant modulus algorithm (CMA), considering white or colored inputs and stationary or nonstationary environments. Since the desired universal behavior of the combination depends on the correct estimation of the mixing parameter at every instant, its adaptation is also taken into account in the transient analysis. Furthermore, we propose normalized algorithms for the adaptation of the mixing parameter that exhibit good performance. Good agreement between analysis and simulation results is always observed.

Distributed Estimation Over an Adaptive Incremental Network Based on the Affine Projection Algorithm

We study the problem of distributed estimation based on the affine projection algorithm (APA), which is developed from Newton`s method for minimizing a cost function. The proposed solution is formulated to ameliorate the limited convergence properties of least-mean-square (LMS) type distributed adaptive filters with colored inputs. The analysis of transient and steady-state performances at each individual node within the network is developed by using a weighted spatial-temporal energy conservation relation and confirmed by computer simulations. The simulation results also verify that the proposed algorithm provides not only a faster convergence rate but also an improved steady-state performance as compared to an LMS-based scheme. In addition, the new approach attains an acceptable misadjustment performance with lower computational and memory cost, provided the number of regressor vectors and filter length parameters are appropriately chosen, as compared to a distributed recursive-least-squares (RLS) based method.

Cryogenic operation of FinFETs aiming at analog applications

FinFETs are recognized as promising candidates for the CMOS nanometer era. In this paper the most recent results for cryogenic operation of FinFETs will be demonstrated with special emphasis on analog applications. Threshold voltage, subthreshold slope and carrier mobility will be studied. Also some important figures of merit for analog circuit operation as for readout electronics, such as transconductance, output conductance and intrinsic voltage gain will be covered. It is demonstrated that the threshold voltage of undoped narrow FinFETs is less temperature-dependent than for a planar single-gate device with similar doping concentration. The temperature reduction improves the transconductance over drain current ratio in any operational region. On the other hand, the output conductance is degraded when the temperature is reduced. The combination of these effects shows that the intrinsic gain of a L = 90 nm FinFET is degraded by 2 dB when the temperature reduces from 300 K to 100 K. (C) 2009 Elsevier Ltd. All rights reserved.

Stochastic stability analysis for the constant-modulus algorithm

We derive an easy-to-compute approximate bound for the range of step-sizes for which the constant-modulus algorithm (CMA) will remain stable if initialized close to a minimum of the CM cost function. Our model highlights the influence, of the signal constellation used in the transmission system: for smaller variation in the modulus of the transmitted symbols, the algorithm will be more robust, and the steady-state misadjustment will be smaller. The theoretical results are validated through several simulations, for long and short filters and channels.

Improving the tracking capability of adaptive filters via convex combination

As is well known, Hessian-based adaptive filters (such as the recursive-least squares algorithm (RLS) for supervised adaptive filtering, or the Shalvi-Weinstein algorithm (SWA) for blind equalization) converge much faster than gradient-based algorithms [such as the least-mean-squares algorithm (LMS) or the constant-modulus algorithm (CMA)]. However, when the problem is tracking a time-variant filter, the issue is not so clear-cut: there are environments for which each family presents better performance. Given this, we propose the use of a convex combination of algorithms of different families to obtain an algorithm with superior tracking capability. We show the potential of this combination and provide a unified theoretical model for the steady-state excess mean-square error for convex combinations of gradient- and Hessian-based algorithms, assuming a random-walk model for the parameter variations. The proposed model is valid for algorithms of the same or different families, and for supervised (LMS and RLS) or blind (CMA and SWA) algorithms.

Development and fabrication of an optimized thermo-electro-optic device using a Mach-Zehnder interferometer

The development and fabrication of a thermo-electro-optic sensor using a Mach-Zehnder interferometer and a resistive micro-heater placed in one of the device`s arms is presented. The Mach-Zehnder structure was fabricated on a single crystal silicon substrate using silicon oxynitride and amorphous hydrogenated silicon carbide films to form an anti-resonant reflective optical waveguide. The materials were deposited by Plasma enhanced chemical vapor deposition technique at low temperatures (similar to 320 degrees C). To optimize the heat transfer and increase the device response with current variation, part of the Mach-Zehnder sensor arm was suspended through front-side bulk micromachining of the silicon substrate in a KOH solution. With the temperature variation caused by the micro-heater, the refractive index of the core layer of the optical waveguide changes due to the thermo-optic effect. Since this variation occurs only in one of the Mach-Zehnder`s arm, a phase difference between the arms is produced, leading to electromagnetic interference. In this way, the current applied to the micro-resistor can control the device output optical power. Further, reactive ion etching technique was used in this work to define the device`s geometry, and a study of SF6 based etching rates on different composition of silicon oxynitride films is also presented. (C) 2007 Elsevier B.V. All rights reserved.

Tunable Bragg filter using silicon compound films

In this work, we present the simulation, fabrication and characterization of a tunable Bragg filter employing amorphous dielectric films deposited by plasma enhanced chemical vapor deposition technique on a crystalline silicon substrate. The optical device was built using conventional microelectronic processes and consisted of fifteen periodic intervals of Si3N4 layers separated by air with appropriated thickness and lengths to produce transmittance attenuation peaks in the visible region. For this, previous simulations were realized based in the optical parameters of the dielectric film, which were extracted from ellipsometry and profilometry techniques. For the characterization of the optical interferential filter, a 633 nm monochromatic light was injected on the filter, and then the transmitted output light was collected and conducted to a detector through an optical waveguide made also of amorphous dielectric layers. Afterwards, the optical filter was mounted on a Peltier thermoelectric device in order to control the temperature of the optical device. When the temperature of filter changes, a refractive index variation is originated in the dielectric film due to the thermo-optic effect, producing a shift of attenuation peak, which can be well predicted by numerical simulations. This characteristic allows this device to be used as a thermo-optic sensor. (C) 2007 Elsevier B.V. All rights reserved.