Ústav radioelektroniky

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Design adaptation of an electronically tunable oscillator using a low performance linearized CMOS operational transconductance amplifier
(2025-11-01) Šotner, Roman; Polák, Ladislav; Langhammer, Lukáš; Andriukaitis, Darius
This paper presents the implementation of commercially available CMOS devices with unfavorable properties, such as low output resistance, in an application designed to mitigate these limitations. By employing a specific topology and considering key design parameters, the proposed approach minimizes the adverse effects of low output resistance. This design focuses on a linearized operational transconductance amplifier (OTA) based on CMOS transistors, featuring with very low output resistance. This OTA is further integrated into an LC oscillator, where the associated disadvantages are suppressed through a specialized topology and careful selection of parameter values that are unaffected by the low OTA output resistance. The operational verification targets a frequency range of several hundred kHz and a linearly processed voltage range of several hundred mV. The linearized OTA-based low-gain amplifier/attenuator offers a linearity error within -7% (+/- 500 mV). The proposed OTA implementation in the oscillator introduces highly simplified method for adjusting the oscillation condition using a single grounded element while minimizing the adverse effects of low output resistance of OTA. Additionally, the tunability of the oscillator using varactor diodes achieving a range from 120 kHz to 273 kHz for a voltage varying from 0 V to 5 V.
A Memristive Associative Learning Circuit for Fault-Tolerant Multi-Sensor Fusion in Autonomous Vehicle
(2025-07-10) Bhardwaj, Kapil; Semenov, Dmitrii; Šotner, Roman; Majumdar, Sayani
Autonomous vehicles completely rely on accurate multi-sensor fusion to perceive their environment and make driving decisions. However, conventional AI-based perception systems face challenges in irregular conditions such as poor visibility, occlusions, or adverse weather conditions, which can lead to incomplete or degraded information from sensors reaching the central computing/navigation system. This severely impacts perception accuracy, potentially compromising vehicle, and pedestrian safety. This work presents a memristor-based associative learning circuit that enhances fault tolerance by dynamically adapting to multi-sensor inputs, including camera, LiDAR, radar, and ultrasonic sensors. The proposed circuit dynamically reinforces patterns, allowing the system to retain decision-making capabilities even when certain sensors fail or provide incomplete data. The fault tolerance of the circuit is validated through error analysis, proving that accurate outputs are generated even with missing sensor inputs. The system demonstrates an average error of 6.98% across 10 critical driving scenarios, with a power consumption of approximate to 152 mW per scenario, confirming its robustness, energy efficiency and adaptability in case of sensor failures and under-performance. The response time of the circuit has been optimized from milliseconds to seconds, aligning with realistic human-like reaction times required for autonomous navigation.
Series-, Parallel-, and Inter-Connection of Solid-State Arbitrary Fractional-Order Capacitors: Theoretical Study and Experimental Verification
(IEEE, 2018-02-27) Kartci, Aslihan; Agambayev, Agamyrat; Herencsár, Norbert; Salama, Khaled Nabil
In the paper, general analytical formulas are introduced for the determination of equivalent impedance, magnitude, and phase, i.e. order, for n arbitrary fractional-order capacitors (FoCs) connected in series, parallel, and their interconnection. The approach presented helps to evaluate these relevant quantities in the fractional domain since the order of each element has a significant effect on the impedance of each FoC and their equivalent capacitance cannot be considered. Three types of solid-state fractional-order passive capacitors of different orders, using ferroelectric polymer and reduced Graphene Oxide-percolated P(VDF-TrFE-CFE) composite structures, are fabricated and characterized. Using an impedance analyzer, the behavior of the devices was found to be stable in the frequency range 0.2MHz–20MHz, with a phase angle deviation of ±4 degrees. Multiple numerical and experimental case studies are given, in particular for two and three connected FoCs. The fundamental issues of the measurement units of the FoCs connected in series and parallel are derived. A MATLAB open access source code is given in Appendix for easy calculation of the equivalent FoC magnitude and phase. The experimental results are in good agreement with the theoretical assumptions.
New Compact VM Four-Phase Oscillator Employing Only Single Z-Copy VDTA And All Grounded Passive Elements
(Kaunas University of Technology, 2013-12-16) Herencsár, Norbert; Šotner, Roman; Koton, Jaroslav; Mišurec, Jiří; Vrba, Kamil
In this paper, a new compact voltage-mode four-phase oscillator employing single z-copy voltage differencing transconductance amplifier (ZC-VDTA) and only grounded passive elements is introduced. The use of only grounded capacitors and resistors makes the proposed circuit ideal for integrated circuit implementation. The condition of oscillation and the frequency of oscillation are independently adjustable. The passive and active sensitivities of the proposed circuit configuration are low. Experimental measurement results using readily available Maxim Integrated ICs MAX435 are given to prove the theory.
Position-Specific Statistics of 60 GHz Vehicular Channels During Overtaking
(IEEE, 2019-01-15) Zöchmann, Erich; Hofer, Markus; Lerch, Martin; Pratschner, Stefan; Bernado, Laura; Blumenstein, Jiří; Caban, Sebastian; Sangodoyin, Seun; Groll, Herbert; Zemen, Thomas; Prokeš, Aleš; Rupp, Markus; Molisch, Andreas F.; Mecklenbräuker, Christoph
The time-variant vehicle-to-vehicle radio propagation channel in the frequency band from 59.75 to 60.25 GHz has been measured in an urban street in the city center of Vienna, Austria. We have measured a set of 30 vehicle-to-vehicle channel realizations to capture the effect of an overtaking vehicle. Our experiment was designed for characterizing the large-scale fading and the small-scale fading depending on the overtaking vehicle's position. We demonstrate that large overtaking vehicles boost the mean receive power by up to 10 dB. The analysis of the small-scale fading reveals that the two-wave with diffuse power (TWDP) fading model is adequate. By means of the model selection, we demonstrate the regions where the TWDP model is more favorable than the customarily used the Rician fading model. Furthermore, we analyze the time selectivity of our vehicular channel. To precisely define the Doppler and delay resolutions, a multitaper spectral estimator with discrete prolate spheroidal windows is used. The delay and Doppler profiles are inferred from the estimated local scattering function. Spatial filtering by the transmitting horn antenna decreases the delay and Doppler spread values. We observe that the RMS Doppler spread is below one-tenth of the maximum Doppler shift 2f v/c. For example, at 60 GHz, a relative speed of 30 km/h yields a maximum Doppler shift of approximately 3300 Hz. The maximum RMS Doppler spread of all observed vehicles is 450 Hz; the largest observed RMS delay spread is 4 ns.

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