2014/3

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    All-Pole Recursive Digital Filters Design Based on Ultraspherical Polynomials
    (Společnost pro radioelektronické inženýrství, 2014-09) Stojanovic, Nikola; Stamenkovic, Negovan; Stojanovic, Vidosav
    A simple method for approximation of all-pole recursive digital filters, directly in digital domain, is described. Transfer function of these filters, referred to as Ultraspherical filters, is controlled by order of the Ultraspherical polynomial, nu. Parameter nu, restricted to be a nonnegative real number (nu ≥ 0), controls ripple peaks in the passband of the magnitude response and enables a trade-off between the passband loss and the group delay response of the resulting filter. Chebyshev filters of the first and of the second kind, and also Legendre and Butterworth filters are shown to be special cases of these allpole recursive digital filters. Closed form equations for the computation of the filter coefficients are provided. The design technique is illustrated with examples.
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    A Closed-Form Approximated Expression for the Residual ISI Obtained by Blind Adaptive Equalizers with Gain Equal or Less than One
    (Společnost pro radioelektronické inženýrství, 2014-09) Kupchan, Simon; Pinchas, Monika
    In this paper we propose for the real and two independent quadrature carrier case, a closed-form approximated expression for the achievable residual Inter-Symbol Interference (ISI) that depends on the step-size parameter, equalizer’s tap length, equalized output gain, input signal statistics, channel power and SNR. This expression is valid for blind adaptive equalizers, where the error that is fed into the adaptive mechanism which updates the equalizer‘s taps can be expressed as a polynomial function of order three of the equalized output and where the gain between the input and equalized output signal is less than or equal to one, as is in the case of Godard (gain = 1) and WNEW (gain < 1) algorithm. Since the channel power is measurable or can be calculated if the channel coefficients are given, there is no need to carry out simulation with various step-size parameters in order to reach the required residual ISI. In addition, we show two new equalization methods (gain dependent), which have shown to have improved equalization performance compared to Godard and WNEW.
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    Simple Floating Voltage-Controlled Memductor Emulator for Analog Applications
    (Společnost pro radioelektronické inženýrství, 2014-09) Fouda, Mohamed E.; Radwan, Ahmed G.
    The topic of memristive circuits is a novel topic in circuit theory that has become of great importance due to its unique behavior which is useful in different applications. But since there is a lack of memristor samples, a memristor emulator is used instead of a solid state memristor. In this paper, a new simple floating voltage-controlled memductor emulator is introduced which is implemented using commercial off the shelf (COTS) realization. The mathematical modeling of the proposed circuit is derived to match the theoretical model. The proposed circuit is tested experimentally using different excitation signals such as sinusoidal, square, and triangular waves showing an excellent matching with previously reported simulations.
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    Modeling the Flux-Charge Relation of Memristor with Neural Network of Smooth Hinge Functions
    (Společnost pro radioelektronické inženýrství, 2014-09) Mu, Xiaomu; Yu, Juntang; Wang, Shuning
    The memristor was proposed to characterize the flux-charge relation. We propose the generalized flux-charge relation model of memristor with neural network of smooth hinge functions. There is effective identification algorithm for the neural network of smooth hinge functions. The representation capability of this model is theoretically guaranteed. Any functional flux-charge relation of a memristor can be approximated by the model. We also give application examples to show that the given model can approximate the flux-charge relation of existing piecewise linear memristor model, window function memristor model, and a physical memristor device.
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    Digital Offset Calibration of an OPAMP Towards Improving Static Parameters of 90 nm CMOS DAC
    (Společnost pro radioelektronické inženýrství, 2014-09) Arbet, Daniel; Nagy, Gabriel; Stopjakova, Viera; Kovac, Martin
    In this paper, an on-chip self-calibrated 8-bit R-2R digital-to-analog converter (DAC) based on digitally compensated input offset of the operational amplifier (OPAMP) is presented. To improve the overall DAC performance, a digital offset cancellation method was used to compensate deviations in the input offset voltage of the OPAMP caused by process variations. The whole DAC as well as offset compensation circuitry were designed in a standard 90 nm CMOS process. The achieved results show that after the self-calibration process, the improvement of 48% in the value of DAC offset error is achieved.