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Author: search.filters.author.Jerabek, JanSubject: search.filters.subject.Electronic control

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    Exponentially tunable voltage controlled quadrature oscillator
    (2017-10-19)
    Sotner, Roman
    ;
    Jerabek, Jan
    ;
    Petrzela, Jiri
    ;
    Domansky, Ondrej
    ;
    Jaikla, Winai
    This paper deals with appropriate method of tunability extension in quadrature oscillators. Exponential dependence of frequency of oscillations on DC control voltage is created in lossless integrators by utilization of two exponentially controlled variable gain amplifiers and diamond transistors. Proposed solution maintains all beneficial features (especially independent levels of output waveforms on tuning process) of the oscillator concept employing two lossless integrators in the single loop and electronically controllable negative resistor serving for adjusting of condition of oscillations. PSpice verifications based on simulations of macromodels of used active devices confirmed doubled tunability range in comparison to standard linear control of frequency obtained for the same change of DC driving voltage.
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    Comparison of Two Solutions of Quadrature Oscillators With Linear Control of Frequency of Oscillation Employing Modern Commercially Available Devices
    (2015-11-23)
    Sotner, Roman
    ;
    Jerabek, Jan
    ;
    Langhammer, Lukas
    ;
    Polak, Josef
    ;
    Herencsar, Norbert
    This paper proposes two circuits of frequency-controlled oscillators, whose structures are based only on simple commercially available active elements with minimum number of terminals, in particular, the differential voltage buffer, controllable voltage amplifier and electronically controllable current conveyor. Two methods for achieving linear control (tuning) of frequency of oscillations (FO) are discussed. The first method employs a simple structure. However, the generated signal level (amplitude) depends on the tuning process. This is a drawback of this method. The second method solves this drawback completely, and the generated signals have constant amplitudes during the tuning of FO. The expected behavior is confirmed by laboratory experiments utilizing commercially available high-speed active elements (current- and voltage-mode multipliers, video difference amplifier). Operational range was tested from frequencies of hundreds of kHz up to frequencies of tens of MHz.
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    Novel first-order all-pass filter applications of z-copy voltage differencing current conveyor
    (2015-08-01)
    Sotner, Roman
    ;
    Herencsar, Norbert
    ;
    Jerabek, Jan
    ;
    Vrba, Kamil
    ;
    Dostal, Tomas
    The application of z-copy voltage differencing current conveyor (ZC-VDCC) in simple and interesting first-order allpass sections has been studied in the present paper. The solutions presented here have presumptions for direct electronic control. Some of proposed circuits offer curious possibilities of control. Electronic controllability of the VDCC allows simultaneous zero and pole frequency adjusting, separated zero or pole frequency adjusting or migration of zero from left half plane to right half plane of complex space. Behavioral models of VDCC based on commercially available devices are proposed and selected type of all-pass section was verified by simulations and also by measurements. Results of simulations, experiments, and theoretical proposal are compared. Experiments confirm workability of proposed behavioral equivalent circuit in bandwidths to units of MHz.