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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
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Polak, Ladislav
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Petrzela, Jiri
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Semenov, Dmitrii
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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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Integer- And fractional-order VCO using non-inertial amplitude stabilization and modern active elements
(2020-04-28)
Sotner, Roman
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Petrzela, Jiri
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Jerabek, Jan
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Langhammer, Lukas
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Polak, Josef
This paper introduces design of the linearly tunable quadrature voltage-controlled oscillator (VCO) using modern off-the-shelf active elements suitable for the design of electronically adjustable applications. The simplified topology was achieved using non-inertial stabilization of amplitude. It allows targeting adjustability of the oscillation frequency only into lossless integrator part of the topology. This arrangement simplifies the design and the tenability also. Derived symbolical expressions indicate that gain adjustment of used amplifiers (that are still in single path) does not influence amplitude and phase shift ratio of generated waveforms, which is a beneficial feature. The performances of the circuit are tested experimentally in band of units of MHz and results confirmed expected behavior. Initial study of the oscillator with fractional-order capacitors is presented and discussed. Results are supported by laboratory measurements.
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Illuminance sensing in agriculture applications based on infra-red short-range compact transmitter using 0.35 μm CMOS active device
(2020-01-01)
Sotner, Roman
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Jerabek, Jan
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Polak, Ladislav
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Petrzela, Jiri
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Jaikla, Winai
This paper introduces a novel electronic system for simplex low-bitrate infra-red (IR) communication applications. The transmitter is implemented completely by analog building blocks, formed with the help of a recently fabricated chip that includes active elements allowing various modular interconnections. For the design of this chip, the ON Semiconductor C035~0.35μm I3T25 technology was chosen due to the trade-off between cost, efficiency and obtainable parameters. The designed transmitter operates as a voltage-to-duty cycle converter, using pulse width modulation that causes ON/OFF keying of the carrier signal for infra-red (IR) diode. The duty cycle variable between 7% and 83% is modulated by the input voltage (in the range of ±0.8 V) of the transmitter. The use case of the proposed concept in the measurement of illuminance within the range of 30 lx and 550 lx is also presented. The quality of the transmission was evaluated as the error between the transmitted and received values of the duty cycle (kept mostly below 10 %). The maximal power consumption of the transmitter reaches 180 mW.
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Voltage Differencing Current Conveyor Differential Input Transconductance Amplifier: Novel Active Element and Its Resistorless Filtering Application
(2019-10-01)
Sotner, Roman
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Jerabek, Jan
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Langhammer, Lukas
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Petrzela, Jiri
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Jaikla, Winai
This paper introduces novel modification of active element based on current conveyor transconductance amplifier core abbreviated as current controlled voltage differencing current conveyor differential input transconductance amplifier (CC-VDCCDITA). The active element is implemented by recently developed and manufactured IC modular device based on I3T25 0.35 μm ON Semiconductor CMOS process. Active element uses three internal active cells of this IC device for construction of the CC-VDCCDITA. An application example of proposed element in simple special resistor-less electronically adjustable biquadratic filter is shown. Brief comparison with state-of-the-art solutions indicates beneficial features of proposed solution. Simulation results in Cadence IC tool accompany precise laboratory experimental measurements with real prototype.
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Reconnection-less Reconfigurable Filter and its Application into Adaptive Circuit
(2018-08-20)
Sotner, Roman
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Jerabek, Jan
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Petrzela, Jiri
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Langhammer, Lukas
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Domansky, Ondrej
This paper presents special topology of a reconnection-less reconfigurable second-order filter. Its features of available transfer functions are unique, because none of the previously reported solutions provides similar features. Our concept is easily implementable thanks to the simple commercial active devices as shown in the paper. The design specifications and transfer responses are analyzed by PSpice simulations. Application example of the high-pass response with adjustable low-frequency stop-band attenuation in adaptive signal processing is shown. All results are following theoretical expectations.
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Exponentially tunable voltage controlled quadrature oscillator
(2017-10-19)
Sotner, Roman
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Jerabek, Jan
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Petrzela, Jiri
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Domansky, Ondrej
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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
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Jerabek, Jan
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Langhammer, Lukas
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Polak, Josef
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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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