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Voltage-Controlled Sinusoidal Oscillator Using Commercially Available ICs with Amplitude Adjustability and Its Application to FM and FSK Modulations for Transmission and Processing of Identified Low-Frequency Signals
(2026-04-01)
Suwanjan, Peerawut
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Adhan, Suchin
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Chaichana, Amornchai
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Sotner, Roman
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Nramat, Wichai
This paper presents a new voltage-controlled sinusoidal oscillator employing only two commercially available LT1228 integrated circuits, four resistors, and two capacitors. The proposed oscillator provides independent control of oscillation frequency and oscillation condition, as well as adjustable output amplitude, while maintaining low output impedance without requiring additional active components. The oscillation frequency is electronically and linearly tuned via the LT1228 bias current or control voltage. Experimental results confirm the practicality of the design: The proposed VCO achieves a wide linear tuning range from 9.25 kHz to 837.2 kHz, THD below 2.55%, and phase noise of –73.35 dBc/Hz at a 1 kHz offset for a 237.8 kHz carrier. The amplitude of the sinusoidal output is adjustable from 0.48 Vp-p to 6.64 Vp-p. In addition, the proposed VCO is successfully applied to FM and FSK modulation for low-frequency signal transmission, and the FM demodulation test yields a recovered sawtooth signal with an SNR of 34.51 dB. Compared with existing LT1228-based oscillators, the proposed circuit achieves 25% lower power consumption (149 mW) and reduces the number of ICs required while improving functional versatility. These results validate the effectiveness and novelty of the proposed LT1228-based design.
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Reconfigurable versatile temperature-insensitivity immittance simulators with electronic tunability using commercially available ICs
(2026-01-01)
Kulapong, Worawut
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Sotner, Roman
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Khateb, Fabian
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Jaikla, Winai
This paper presents novel reconfigurable and electronically tunable immittance simulators using commercially available LT1228 integrated circuits. The proposed circuits simulate four fundamental impedance functions, which are a resistor, a capacitor, an inductor, and a frequency-dependent negative resistor (FDNR) within the same topology. The proposed simulators use only two or three LT1228 ICs and three passive components to provide grounded and floating types, be compact, and function in a variety of ways. A significant contribution of this work is the development of an impedance expression that does not depend on temperature. This makes sure that performance stays stable over a wide range of temperatures without the need for external compensation techniques. The proposed circuits offer linear electronic control via bias currents, enabling precise and dynamic tuning of the simulated element values. Moreover, the proposed simulators can be configured to four lossless impedance functions without needing the matching conditions of passive elements. A study of the parasitic effect is also conducted to assess accuracy and useful frequency range of the proposed configuration. Both grounded and floating configurations are realized and validated through simulation and experimental results. A third-order low-pass ladder filter and a multifunction second-order filter are designed to show the applications of the proposed simulators. The accuracy, reconfigurability, and temperature stability of the proposed circuits are confirmed by the simulation and experimental results, which make them ideal for modern analog signal processing applications. Temperature stability is verified via PSpice simulation over –100 °C to + 100 °C, showing less than 1 % variation, while impedance accuracy and filter applications are confirmed experimentally.
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Design of Constant Phase Elements for Adjustable Pseudocapacitance by a Single Driving Voltage Using Integrated Unipolar Transistor Fields
(2026-01-01)
Sotner, Roman
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Litovska, Anna
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Polak, Ladislav
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Jerabek, Jan
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Kledrowetz, Vilem
This paper presents the design of a passive fractional-order element with tunable pseudocapacitance, enabling adaptable circuit behavior without additional power consumption. This is an important feature for modelling and characterization in natural systems, as well as in the field of electrical and electronic engineering, particularly for the design of instrumentation and sensing systems. The proposed topologies are based on integrated unipolar transistor arrays. Two implementations are demonstrated, with fractional orders of 0.22 and 0.5, offering pseudocapacitance adjustment ranges from 65 to 1 670 mikroF/s^0.78 and from 6.7 to 51 mikroF/s^0.5, respectively. Tuning is achieved through a DC bias voltage ranging from 0.8 to 10 V. The devices operate across nearly two decades of frequency, from approximately 100 Hz to 200 kHz, and support signal amplitudes in the hundreds of millivolts. Two application examples highlight their potential: electronic tuning of the center frequency in a fractional-order band-pass filter, and adjustment of the oscillation frequency in a fractional-order oscillator with a fixed 22.5 degrees phase shift between output waves. All concepts and results are experimentally validated in the laboratory.
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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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Electronically controlled square/triangular wave generator with amplitude adjustability and its application in light intensity measurement using commercial-off-the-shelf current feedback amplifiers
(2025-07-01)
Choykhuntod, Pawich
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Sotner, Roman
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Silapan, Phamorn
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Kaewon, Rapeepan
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Jaikla, Winai
This study presents a square and triangular waveform generator using two commercial-off-the-shelf current feedback amplifiers with DC gain control, LT1228. The frequency of the square and triangular waveforms can be electronically and independently adjusted with the bias current. With this advantage feature, the proposed generator can be easily modified to generate a sawtooth waveform and electronically adjust the duty cycle of square waves. Additionally, PWM signals can also be generated from the proposed circuit. The amplitude of both square and triangular waveforms is adjustable without affecting the frequency, and the output nodes have low impedance. The circuit's performance is validated through practical implementation and testing, showing excellent agreement with theoretical analysis. The measured linear and electronic adjustment of frequency spanned from 4.83 kHz to 436.2 kHz. Furthermore, the circuit can be applied as a low-cost light intensity detection sensor.
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Single Commercially Available Integrated Circuit-based Sinusoidal Oscillators with Amplitude Adjustability and Electronic Control of Condition
(2024-09-01)
Duangkaew, Suleeporn
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Supavarasuwat, Piya
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Siripruchyanun, Montree
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Sotner, Roman
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Jaikla, Winai
This paper presents four new sinusoidal oscillators using a commercially available integrated circuit (IC). The proposed circuits are simple topologies that employ a single commercial IC, LT1228. It is connected to passive element, consisting of four resistors and two capacitors. All derived oscillator circuits have low output impedance, allowing them to connect to other circuits without requiring an additional buffer. Using an active LT1228 device enables electronic adjustment of parameters in the proposed circuits. A feedback resistor can be used to change the output signal's amplitude without affecting the oscillation's frequency or condition. We performed both simulations using the PSPICE program and experiments to confirm the accuracy of all proposed oscillator circuits. The best total harmonic distortion was 0.13% for the proposed oscillator circuit 3. Adjusting the maximum amplitude using a resistor provides a gain of roughly 1.5–16.5 dB for the proposed oscillator circuit no. 1.
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Compact active analog device for novel applications useful for sensing and measurement
(2024-08-01)
Sotner, Roman
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Jerabek, Jan
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Polak, Ladislav
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Jaikla, Winai
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Andriukaitis, Darius
The presented research introduces a novel approach to modern modular active device and provides various practical application examples tailored for industrial sensing readouts. Straightforward implementation of single active device-based topologies in frequency bands from kHz up to MHz is presented. These applications include: an electronically linearly tunable special band-pass filter that can be easily modified into a voltage-controlled oscillator, a two-port quadratic transformer, an amplitude modulator, and an equalization circuit (which serves as a fractional-order differentiator and integrator). These circuits benefit from high-impedance voltage input and low-impedance output (easily matched to 50 Ω), high processed signal levels (often reaching hundreds of mV), and simplified topologies without redundant passive elements. These features are especially valuable in tunable and configurable solutions for modern communication, sensing, audio, and consumer electronic systems, as well as in modeling various physical and biological systems. The experiments have been provided by simulations and measurements using device VCA824.
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Gain-Controllable Transadmittance-Mode First-Order Allpass Filters with Electronic Tune Using Single Active Element
(2024-02-01)
Tanaphatsiri, Chaiya
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Khateb, Fabian
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Sotner, Roman
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Jaikla, Winai
First-order allpass filters are analog filters with a unit magnitude response, but they change the phase shift between input and output signals at various frequencies. This paper presents the transadmittance-mode first-order allpass filters based on the modified current-controlled current differencing transconductance amplifier (M-CCCDTA). The proposed filters utilize a single M-CCCDTA and a grounded capacitor with no external resistors, making them well suited for implementation in an integrated circuit. The gain and phase response of the proposed filters can be adjusted electronically and separately. Also, the high output impedance of the proposed filters at both the input voltage node and the output current node makes cascading easy without the need for buffer devices. A quadrature sinusoidal oscillator based on the proposed first-order allpass filter has been designed as an example of an application. The PSpice simulation and actual experiments are utilized to validate the functionality of the proposed filters. The simulation and experimental results are consistent with the idea of anticipation.
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Special Transfer Section for Selective Rejecting and Amplification of Bands in Equalization
(2024-01-01)
Sotner, Roman
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Svoboda, Marek
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Semenov, Dmitrii
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Polak, Ladislav
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Jerabek, Jan
This paper introduces a novel and simple filtering topology for band-reject (notch) and inverse band-reject applications, utilizing two voltage-adjustable operational transconductance amplifiers. The utilization of these active devices enables the implementation of identical topologies for both band-reject and inverse band-reject transfer functions. The resulting responses are harnessed for the cascade synthesis of a specialized comb filter, capable of amplification or attenuating/rejecting specific bands shown on three sub-bands. Both the design of individual sections and the entire cascade have been experimentally verified using active devices manufactured in the TSMC 180 nm CMOS process. Measurements conducted over a range from 10 Hz to 100 kHz demonstrate the importance of the selective filtering, which is significant for various applications, particularly in acoustic, vibration, and magnetic sensing readouts. The example of peaking suppression in magnitude response of emulated environment (acoustic coupling of piezo and microphone) is shown.
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Design of Phase-Locked Loop Using Special Analog Multipliers and Voltage Buffers: Demodulation of Transposed Signals from Sensors
(2024-01-01)
Svoboda, Marek
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Sotner, Roman
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Polak, Ladislav
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Jerabek, Jan
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Jaikla, Winai
Phase-locked loops (PLLs) are versatile electronic circuits that, among others, are used in various sensor applications (e.g., medical) for their ability to generate stable and precise clock signals. This article introduces a novel PLL-based frequency demodulation system designed for processing of very slow signals, ranging from a few Hz to several hundreds of Hz, with amplitudes in the order of several hundreds of millivolts. The system incorporates specialized analog multipliers tailored for essential PLL components, including the voltage-controlled oscillator, phase detector, loop filter with variable DC offset, and baseband filter, all optimized for the purpose of frequency demodulation. These multipliers were fabricated using the TSMC 0.18~μ m, 1.8 V CMOS process. The primary design objectives are simplicity, reduced complexity, low power consumption (merely 15 mW), and versatility for applications in sensing engineering. To validate the functionality of the proposed PLL system under practical conditions, we present an example of electrocardiogram and photoplethysmogram signal demodulation, demonstrating its operational performance.

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