2016/2

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    A Geometric Approach to Group Delay Network Synthesis
    (Společnost pro radioelektronické inženýrství, 2016-06) Osuch, Piotr Jan; Stander, Tinus
    All-pass networks with prescribed group delay are used for analog signal processing and equalisation of transmission channels. The state-of-the-art methods for synthesising quasi-arbitrary group delay functions using all-pass elements lack a theoretical synthesis procedure that guarantees minimum-order networks. We present an analytically-based solution to this problem that produces an all-pass network with a response approximating the required group delay to within an arbitrary minimax error. For the first time, this method is shown to work for any physical realisation of second-order all-pass elements, is guaranteed to converge to a global optimum solution without any choice of seed values as an input, and allows synthesis of pre-defined networks described both analytically and numerically. The proposed method is also demonstrated by reducing the delay variation of a practical system by any desired amount, and compared to state-of-the-art methods in comparison examples.
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    Novel CMOS Bulk-driven Charge Pump for Ultra Low Input Voltage
    (Společnost pro radioelektronické inženýrství, 2016-06) Nagy, Gabriel; Arbet, Daniel; Stopjakova, Viera; Kovac, Martin
    In this paper, a novel bulk-driven cross-coupled charge pump designed in standard 90 nm CMOS technology is presented. The proposed charge pump is based on a dynamic threshold voltage inverter and is suitable for integrated ultra-low voltage converters. Due to a latchup risk, bulk-driven charge pumps can safely be used only in low-voltage applications. For the input voltage below 200 mV and output current of 1 uA, the proposed bulk-driven topology can achieve about 10 % higher efficiency than the conventional gate-driven cross-coupled charge pump. Therefore, it can be effectively used in DC-DC converters, which are the basic building blocks of on-chip energy harvesting systems with ultra-low supply voltage.
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    Efficient Design of Digital FIR Differentiator using $L_1$-Method
    (Společnost pro radioelektronické inženýrství, 2016-06) Aggarwal, Apoorva; Rawat, T. K.; Kumar, Manjeet; Upadhyay, D. K.
    In this paper, an efficient design of FIR digital differentiator using the L1-optimality criterion is proposed. We present a technique based on the modified Newton method to solve the design problem so that the optimal differentiator coefficients are obtained by minimizing the absolute error. The novel L1-error function leads to a flat response at low-frequencies. Extensive simulations are carried out to validate the proposed design. The superiority of the proposed design is evident by comparing it with other conventional design techniques such as, windowing, minimax and the least-squares approach.
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    Grey Box Non-Linearities Modeling and Characterization of a BandPass BAW Filter
    (Společnost pro radioelektronické inženýrství, 2016-06) Mabrouk, Mohamed; Boujemaa, Mohamed-Ali; Choubani, Fethi
    In this work, the non-linearities of a 3G/UMTS geared BandPass Bulk Acoustic Wave ladder filter composed of five resonators were modeled using non-linear modified Butterworth-Van Dyke model. The non-linear characteristics were measured and simulated, and they were compared and found to be fairly identical. The filter's central frequency is 2.12 GHz, the corresponding bandwidth is 61.55 MHz, and the quality factor is 34.55.
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    Analysis of Intermodulation Distortion in OFDM Based Transmitter Using EER Technique
    (Společnost pro radioelektronické inženýrství, 2016-06) Matejka, Stepan
    During the last two decades, new digital modulation systems have appeared in the audio broadcasting. Such broadcasting systems require new transmitters’ concepts to enable the transmission of digitally modulated signals. Moreover, the selected modulation schemes (e.g. orthogonal frequency division multiplexing) require a high linearity power stage, which typically exhibits low efficiency due to high peak-toaverage power ratio of the modulated signal. One of the promising transmitter concepts is the Kahn envelope elimination and restoration technique, where the original Cartesian in-phase and quadrature baseband signals are transformed to the envelope and phase signals. The main advantage of this technique is an ability to employ suitable types of highly efficient amplitude modulation transmitters for envelope amplification, while the phase modulated carrier is produced by an additional phase modulator. The substantial drawback of envelope elimination and restoration is nonideal recombination of linearly distorted amplitude signal and phase modulated carrier at the output power stage. The aim of this paper is twofold. Firstly, to analyze the effect of the envelope and phase signals bandwidth limitation on the modulated signal in-channel distortion and out-ofchannel emission. Secondly, to present the performance results as a reference for transmitter designers to properly set the envelope and phase paths to reach required in-channel signal quality and suppress out-of-channel products.