2009/3

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    Performances of Hybrid Amplitude Shape Modulation for UWB Communications Systems over AWGN Channel in a Single and Multi-User Environment
    (Společnost pro radioelektronické inženýrství, 2009-09) Herceg, Marijan; Matic, Tomislav; Svedek, Tomislav
    This paper analyzes the performance of the hybrid Amplitude Shape Modulation (h-ASM) scheme for the time-hopping ultra-wideband (TH-UWB) communication systems in the single and multi-user environment. h-ASM is the combination of Pulse Amplitude Modulation (PAM) and Pulse Shape Modulation (PSM) based on modified Hermite pulses (MHP). This scheme is suitable for high rate data transmission applications because b = log2(MN) bits can be mapped with one waveform. The channel capacity and error probability over AWGN channel are derived and compared with other modulation schemes.
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    Reader’s Comment on: Application of the Global Optimization Approaches to Planar Near-Field Antenna Phaseless Measurements
    (Společnost pro radioelektronické inženýrství, 2009-09) Prochazka, Miroslav
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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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    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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    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.