Alfonso Carlosena

Novel transimpedance filter topologies for instrumentation

In this paper two novel distinct transimpedance filter topologies are described. The first one is based on the well known multiple feedback (MFB) filters while the second resembles typical Q-enhancement configurations. For both classes low- and band-pass responses have been fully developed taking into consideration several parameters: frequency response, input-output impedances and noise. Q-enhancement filters have been found to be more versatile if several parameters are to be optimized, at the expense of using more amplifiers. Transimpedance filters find direct application in some sensors and D/A converters which provide current as an output signal.

Vibrato in singing voice: the link between source-filter and sinusoidal models

The application of inverse filtering techniques for high-quality singing voice analysis/synthesis is discussed. In the context of source-filter models, inverse filtering provides a noninvasive method to extract the voice source, and thus to study voice quality. Although this approach is widely used in speech synthesis, this is not the case in singing voice. Several studies have proved that inverse filtering techniques fail in the case of singing voice, the reasons being unclear. In order to shed light on this problem, we will consider here an additional feature of singing voice, not present in speech: the vibrato. Vibrato has been traditionally studied by sinusoidal modeling. As an alternative, we will introduce here a novel noninteractive source filter model that incorporates the mechanisms of vibrato generation. This model will also allow the comparison of the results produced by inverse filtering techniques and by sinusoidal modeling, as they apply to singing voice and not to speech. In this way, the limitations of these conventional techniques, described in previous literature, will be explained. Both synthetic signals and singer recordings are used to validate and compare the techniques presented in the paper.

Extending the limits of resolution for narrow-band harmonic and modal analysis: a non-parametric approach

Non-parametric fast Fourier transform-based spectral analysis is an efficient tool for characterization of signals and systems in the frequency domain, but it often suffers from insufficient spectral resolution. Here we propose methods for improving the physical resolution of spectra by redistributing the original spectral information to emulate larger-time observations. This is accomplished either by non-parametric destructive discrete Fourier transform interpolation or by asymmetric time-windowing. The proposed methods are shown to have very good peak discrimination capacity, which together with their low computational complexity makes them good candidates for narrow-band spectral analysis in instrumentation.

Multichannel Blind Deconvolution of Transient Impulsive Signals

Transient impulsive signals concentrate their energy in a short time interval. Impact force signals show this behaviour and play an important role in the study in mechanical systems. Measuring impact forces directly is not always possible and much research has been done in the last decades to develop indirect measuring techniques, which address the inverse problem of estimating the impact force time-history from the responses of the impacted structure. In the literature, most methods perform this difficult task in two steps: First the dynamical properties of the structure are identified and then an inversion procedure is applied to estimate inputs from outputs. However, when the impact location is unknown this approach may not be valid and blind deconvolution techniques must be used. Here, we fully develop a deterministic subspace method for blind deconvolution in a single-input multiple-output (SIMO) environment that does not impose any restrictions on the excitation signals or the impulse response of the propagation channels, apart from finite length and channel diversity

Active RC impedances revisited

The aim of this paper is to review the synthesis, analysis and design of active RC impedances. First of all, major gaps in this classical research topic are identified. Second, a synthesis procedure is outlined to generate op-amp-based circuits which can simulate several classes of impedances of practical interest. From the resulting classification, all circuits are analysed from a perspective wider than those normally used in previous works, yielding some new interesting design conditions. A method is suggested to convert ladder passive prototypes containing either grounded inductors or FDNRs into MOSFET-C equivalent circuits using some of the new structures obtained. Finally, the use of current feedback amplifiers instead of op amps is considered. Experimental results corroborating all our theoretical predictions are incorporated in the work.

A new method for low-capacitance probing

A method is suggested for cancelling the input capacitance of instruments and probes used in measurements. This approach is proposed as an alternative to conventional attenuating passive and active probes. The idea is demonstrated with a practical device that is able to nullify the parasitic capacitance to less than 2 pF without introducing signal attenuation. >

High-order PLL design with constant Phase Margin

In this paper we describe a novel procedure to design high-type high-order Phase Locked Loops (PLLs) from lower order prototypes, preserving a prescribed Phase Margin (PM). The method builds on a model recently proposed by the authors, and is supported by extensive simulations and experimental results, giving up to a type-III fifth-order PLL with a commercial circuit.

A Novel Design Method for Phase-Locked Loops of any Order and Type

In this paper a novel approach to the design of PLLs is presented, which can be used regardless of their order and type. The method stems from the fact that high-frequency poles in the loop filter determine filtering properties of the PLL, while zero-pole (at the origin) pairs determine its Type and thus the loop control dynamics.

Limitations of the MOS Resistive Circuit in MOSFET-C Implementation: Bandwidth, Noise, Offset and Non-Linearity

Significant departures between predicted behaviour and actual performance are observed in opamp based structures containing the so-called MOS Resistive Circuit. In this paper we demonstrate that the usual description of this cell by a simple model of two tunable resistors is not adequate enough to properly describe the MRC operation. A more complete, still simple model is proposed and shown to work by means of some examples. The model is used to characterise and predict the effects that the limited gain and offset of the opamp induces in the MRC operation, increasing the distortion, the expected noise and the output DC offset, and reducing the bandwidth of the system. Finally we give some design guidelines for the optimum application of the MRC.

Use of a CCII — as a universal building block

Abstract This paper purports to show a second generation negative current conveyor (CCII-), which can be used as a basic building block for the design of typical RC-active applications and also to build-up more complex active devices. A practical bipolar circuit has been fabricated to implement the CCII — functionality. Simulation results are provided for such a circuit and a couple of applications are proposed to demonstrate its practical use.