Time-Division Multiplexing Architecture for Hybrid Filter Bank A/D converters

International audienceIn this paper, a new Hybrid Filter Bank (HFB) architecture called Time-Division Multiplexing (TDM) is proposed for HFB-based A/D Converters (ADC). The TDM HFB architecture is firstly extracted considering the TDM components of analog input as new input vector. The TDM HFB-based ADC is then simulated using simply-realizable analysis filters to approve the mathematical formulation of the TDM model. At last, the output resolutions of TDM and classical HFB-based ADC are compared considering practical analog filters including realization errors. It is shown that the TDM architecture is less sensitive to the realization errors than the classical HFB. Besides, the TDM HFB can exploit a blind technique to correct the realization errors in opposite to the classical HFB case

Sensitivity of hybrid filter banks A/D converters to analog realization errors and finite word length

This paper studies the sensitivity of hybrid filter banks (HFB) to analog inaccuracies and finite word implementation. It is shown that very small errors affecting very simple analog structures have a dramatic influence on the performances of the HFB. The influence of the quantization of digital filter coefficients is also studied. A theoretical limit for the error introduced by the quantization of digital filter coefficients is derived

Digital estimation of analog imperfections using blind equalization

International audienceThe analog electronic circuits are always subject to some imperfections. Analog imperfections cause deviations from nominal values of electronic elements. In the case of Linear Time-Invariant (LTI) circuits, the coefficients of the transfer function include some deviations from related typical values leading to the differences between the typical (i.e. design) and the actual transfer functions. In this paper, the analog imperfections are digitally estimated using only the output samples, without any access to the input signal nor to the analog system (blind method). Super Exponential Algorithm (SEA) is used as the blind equalization technique, since it provides rapid convergence. The only assumption is that the input is a non-Gaussian independent and identically distributed (i.i.d.) signal. Using this algorithm, the effects of analog imperfections in the analog circuits can be digitally estimated and possibly compensated without any dependance on the types and the sources of the analog imperfections. It provides the possibility to have an online compensation of the imperfections (realization errors, drifts, etc.). The analog imperfections have been estimated with a precision of §0:2% and §1:3% for the exemplary RC and RLC circuits respectively

Extended frequency-band-decomposition sigma–delta A/D converter

Parallelism can be used to increase the bandwidths of ADC converters based on sigma–delta modulators. Each modulator converts a part of the input signal band and is followed by a digital filter. Unfortunately, solutions using bandpass sigma–delta modulators are very sensitive to the position of the modulators' central frequencies. This paper shows the feasibility of a frequency-band-decomposition (FBD) ADC using continuous time bandpass sigma–delta modulators, even in the case of large analog mismatches. The major benefit of such a solution, called extended-frequency-band-decomposition (EFBD) is its low sensitivity to analog parameters. For example, a relative error in the central frequencies of 4% can be accepted without significant degradation in the performance (other published FBD ADCs require a precision of the central frequencies better than 0.1%). This paper will focus on the performance which can be reached with this system, and the architecture of the digital part. The quantization of coefficients and operators will be addressed. It will be shown that a 14 bit resolution can be theoretically reached using 10 sixth-order bandpass modulators at a sampling frequency of 800 MHz which results in a bandwidth of 80 MHz centered around 200 MHz (the resolution depends on the effective quality factor of the filters of the analog modulators)

Approche paramétrique pour le traitement des signaux ultrasonores : Application à la caractérisation des défauts

La caractérisation des défauts est un objectif majeur en contrôle non destructif. Lors d'un contrôle ultrasonore on n'a pas accès aux défauts, mais seulement à leur représentation à travers les phénomènes physiques mis en jeu et se matérialisant sous la forme d'un signal ultrasonore. L'interprétation de ce signal est souvent difficile et nécessite une certaine expérience de la part de l'opérateur humain. Nous montrons dans cet article l'intérêt d'une approche paramétrique quant à l'extraction, à partir des signaux ultrasonores, de l'information utile concernant le défaut. Il s'agit d'une méthode dont le but est la mise en évidence d'éléments permettant la caractérisation des défauts et qui conduit à une amélioration de la résolution

Influences of oversampling and analog imperfections on Hybrid Filter Bank A/D converters

International audienceHybrid Filter Banks (HFB) are considered as good candidate for implementing wide-band, high-frequency A/D parallel converters. The performance of HFB (original and twostage) structures is analyzed for different values of oversampling ratios leading to the choice of the optimal value. The electronic elements of the analysis filter bank of HFB structure are considered with real constraints (realization errors and drifts). Real analysis filters of HFB are considered with the analog elements for which the real values are randomly Gaussian-distributed. Sensitivity to the deviations from real values is simulated and the performance of two HFB (original and two-stage) structures are compared. The possible methods for decreasing the sensitivity to realization errors such as Total Least Squares (TLS) optimization are discussed. Original structure is found to be a better candidate rather than the two-stage one in practical cases. However, it is shown that a blind estimation method would be necessary to compensate the realization errors for practically implementing the HFB-based A/D converters