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Author: search.filters.author.Petrzela, JiriSubject: search.filters.subject.Variable gain amplifier

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    Differentiator circuits with scalable and electronically adjustable time constant and their application in phase shift evaluation
    (2025-09-01)
    Sotner, Roman
    ;
    Polak, Ladislav
    ;
    Petrzela, Jiri
    ;
    Semenov, Dmitrii
    ;
    Langhammer, Lukas
    Two novel scalable and electronically adjustable differentiator designs are presented in this paper. These designs are based on special variable gain amplifiers extending well-known concept of standard single operational amplifier-based differentiators. The key novelty lies in their scalability, which allows for an enhanced time constant value by adjusting the ratio of resistors. Simultaneously, the special form of gain control using a DC voltage offers wide electronic tunability. The solution performs high input and low output impedance, both independent of frequency. Experimental testing demonstrated time constant adjustments in two configurations: from 64 ns to 4.5 µs (a ratio of maximal and minimal value 70) and from 8.7 µs to 183 µs (a ratio of 21). As an application example, the proposed differentiator is utilized in the design of a readout system for an absolute phase shift difference to pulse width ratio converter, suitable for monitoring a very slow phenomenon such biosignals.
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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.