2009/3

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    Current-Controlled Current-Mode Universal Biquad Employing Multi-Output Transconductors
    (Společnost pro radioelektronické inženýrství, 2009-09) Sotner, Roman; Petrzela, Jiri; Slezak, Josef
    This paper deals with RC active biquad working in the so-called current mode (CM). The design approach uses only three transconductors (OTA) with the minimum necessary number of outputs and with only three passive grounded elements. The proposed filter has simple circuit configuration providing all standard transfer functions such as high-pass (HP), band-pass (BP), low-pass (LP), band-reject (BR) and all-pass (AP). Electronic tuning and independent adjusting of the quality factor and bandwidth of BP filter is possible. The presented circuits are verified by PSpice simulations utilizing OTAs on transistor level of abstraction. The linear parasitic effects of the real active elements in each suggested circuit are briefly discussed. Experimental verification is also given. Designed networks can be used in many applications such as antialiasing filters, in high-speed data telecommunication systems, for signal processing in the cable modems, in regulation and measurement techniques etc.
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    Comparison of Generative and Discriminative Approaches for Speaker Recognition with Limited Data
    (Společnost pro radioelektronické inženýrství, 2009-09) Silovsky, Jan; Cerva, Petr; Zdansky, Jindrich
    This paper presents a comparison of three different speaker recognition methods deployed in a broadcast news processing system. We focus on how the generative and discriminative nature of these methods affects the speaker recognition framework and we also deal with intersession variability compensation techniques in more detail, which are of great interest in broadcast processing domain. Performed experiments are specific particularly for the very limited amount of data used for both speaker enrollment (typically ranging from 30 to 60 seconds) and recognition (typically ranging from 5 to 15 seconds). Our results show that the system based on Gaussian Mixture Models (GMMs) outperforms both systems based on Support Vector Machines (SVMs) but its drawback is higher computational cost.
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    Low Voltage Current Mode Switched-Current-Mirror Mixer
    (Společnost pro radioelektronické inženýrství, 2009-09) Ma, Minglin; Wang, Chunhua; Du, Sichun
    A new CMOS active mixer topology can operate at 1 V supply voltage by use of SCM (switched currentmirror). Such current-mode mixer requires less voltage headroom with good linearization. Mixing is achieved with four improved current mirrors, which are alternatively activated. For ideal switching, the operation is equivalent to a conventional active mixer. This paper analyzes the performance of the SCM mixer, in comparison with the conventional mixer, demonstrating competitive performance at a lower supply voltage. Moreover, the new mixer’s die, without any passive components, is very small, and the conversion gain is easy to adjust. An experimental prototype was designed and simulated in standard chartered 0.18μm RF CMOS Process with Spectre in Cadence Design Systems. Experimental results show satisfactory mixer performance at 2.4 GHz.
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    Imaging of the Building Contours with Through the Wall UWB Radar System
    (Společnost pro radioelektronické inženýrství, 2009-09) Aftanas, Michal; Drutarovsky, Milos
    Any actual information about a building interior can be very useful before entering a dangerous area. It can be used to plan strategies in many rescue and security applications. The paper deals with imaging of the inner and outer building contours from the outside using through the wall UWB radar. The whole processing chain for obtaining the contours of a scanned building is explained. The image processing method of highlighting the building walls using Hough transform with assumed knowledge of the direction of walls is presented. The algorithm was tested on real measurement data acquired from a M-sequence UWB radar system.
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    Derivation of Equivalent Material Models for Composite Laminated Materials
    (Společnost pro radioelektronické inženýrství, 2009-09) Gona, Stanislav; Kresalek, Vojtech
    In this paper, an original approach of derivation of equivalent electrical models for multilayer composite materials is presented. The purpose of the modeling is to approximate a given composite material by an equivalent dielectric slab or by a medium consisting from several dielectric layers. For each layer, an equivalent complex permittivity is set up by an optimization procedure in order to achieve the same values of reflection and transmission coefficients as are the measured values of reflection and transmission coefficients of the original composite material.