Lidia Dobrescu

Dr. Lidia Dobrescu

University”Politehnica” of Bucharest
orcid

Research Focus & Metrics

Academic Career Length

26Years (2001-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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8 November 2002
Verified
Conference Paper
Closed access
Lidia DobrescuLidia Dobrescu
Lidia Dobrescu
MPM. Petrov
M. Petrov
DDD. Dobrescu
D. Dobrescu
Cristian RavariuCristian Ravariu
Cristian Ravariu
The threshold voltage of the MOS transistor is a very important parameter used in all circuit simulation programs. The aim of this paper is to compare several largely applied threshold voltage extraction methods used both for long channel and short channel MOSFETs. This methods use either the linear operation region or the saturation operation region of the transistors. The new derivative extraction method proposed in this paper doesn't depend on the operation region for long channel devices and gives comparable results for short channel devices. It is a very simple and accurate extraction method. The experimental data used in the paper were measured using a HP4155B system. The mathematical calculation and the threshold voltage extraction are performed using MATHCAD designed programs.

22 August 2022 in Applied Sciences
Verified
Journal Article
Open access
PDF file
ELEvdochim Lucian
Evdochim Lucian
DDDragoș Dobrescu
Dragoș Dobrescu
SHStela Halichidis
Stela Halichidis
Lidia DobrescuLidia Dobrescu
Lidia Dobrescu
SSSilviu Marcel Stanciu
Silviu Marcel Stanciu
In our modern digitalized world, hypertension detection represents a key feature that enables self-monitoring of cardiovascular parameters, using a wide range of smart devices. Heart rate and blood oxygen saturation rate are some of the most important ones, easily computed by wearable products that are provided by the photoplethysmography (PPG) technique. Therefore, this low-cost technology has opened a new horizon for health monitoring in the last decade. Another important parameter is blood pressure, a major predictor for cardiovascular characterization and health related events. Analyzing only PPG signal morphology and combining the medical observation with machine learning (ML) techniques, this paper develops a hypertension diagnosis tool, named the ANC Test™. During the development process, distinguishable characteristics have been observed among certain waveforms and certain types of patients that leads to an increased confidence level of the algorithm. The test was enchanted by machine learning models to improve blood pressure class detection between systolic normotensive and hypertensive patients. A total of 359 individual recordings were manually selected to build reference signals using open-source available databases. During the development and testing phases, different ML models accuracy of detecting systolic hypertension scored in many cases around 70% with a maximum value of 72.9%. This was resulted from original waveform classification into four main classes with an easy-to-understand nomenclature. An important limitation during the recording processing phase was given by a different PPG acquisition standard among the consulted free available databases.

3 November 2023 in Electronics
Verified
Journal Article
Open access
PDF file
Cristian StancuCristian Stancu
Cristian Stancu
ANAndrei Neacsu
Andrei Neacsu
TITeodora Ionescu
Teodora Ionescu
CSCornel Stanescu
Cornel Stanescu
OPOvidiu Profirescu
Ovidiu Profirescu
Lidia DobrescuLidia Dobrescu
Lidia Dobrescu
The demand for CMOS precision operational amplifiers for critical applications has continuously increased over time due to higher accuracy and sensitivity requirements. Trimming or chopper architectures are advanced solutions that reduce the offset voltage and improve the circuit’s parameters, but the complexity and the increased chip die size are serious downsides. An efficient solution is a source degeneration configuration to control the transistor’s current-mirror transconductance, which impacts the offset voltage, with cost savings and a die area reduction also obtained. This paper focuses on designing and implementing such an approach in a two-stage folded-cascode operational amplifier. State-of-the-art thin-film resistors that use silicon–chromium as the metallic alloy were implemented to reduce mismatch variations between these passive components. Distinct methods that control the offset voltage parameter are also discussed and established. A comparison between the offset voltage standard deviation obtained using different types of resistors and that achieved with the innovative high-precision resistors was also carried out. The source degeneration’s impact on the common-mode rejection ratio, power supply rejection ratio, bandwidth and phase margin was also analyzed, and a comparison between the proposed design and the classical one was performed. The process variation’s influence on the circuit functionality was studied. A pre-layout ±1.273 mV maximum offset voltage at T = 27 °C was achieved using vector/array notations for the amplifier with the best overall performance. Post-layout simulations that included parasitic effects were performed, with a ±1.254 mV maximum offset voltage reached at room temperature.

1 November 2015
Verified
Conference Paper
Closed access
DTDenis Tudor
Denis Tudor
Lidia DobrescuLidia Dobrescu
Lidia Dobrescu
DDDragos Dobrescu
Dragos Dobrescu
This paper presents a new electronic system using an ATmega328P microcontroller, two ultrasonic sensors and two vibrating motors as a new helping solution for blind people navigation. The block diagram, specific requirements and implementations are described in the paper. Specific design problems and experimental adjustments are mentioned. Future optimizations and developing trends are also considered.

6 October 2023 in Applied Sciences
Verified
Journal Article
Open access
PDF file
ELEvdochim Lucian
Evdochim Lucian
DDDragoș Dobrescu
Dragoș Dobrescu
Lidia DobrescuLidia Dobrescu
Lidia Dobrescu
SSStanciu Silviu
Stanciu Silviu
SHStela Halichidis
Stela Halichidis
Left ventricular ejection time (LVET) is an important parameter for assessing cardiovascular disorders. In a medical office, it is typically measured using the Tissue Doppler Imaging technique, but new wearable devices have led to a growing interest in integrating this parameter into them, increasing accessibility to personalized healthcare for users and patients. In the cardiovascular domain, photoplethysmography (PPG) is a promising technology that shares two distinctive features with invasive arterial blood pressure (ABP) tracing: the tidal wave (TDW) and the dicrotic wave (DCW). In the early years of cardiovascular research, the duration of the dicrotic point was initially linked to the ending phase of left ventricular ejection. Subsequent studies reported deviations from the initial association, suggesting that the ejection period is related to the tidal wave feature. In this current study, we measured left ventricular ejection time in both ABP and PPG waveforms, considering recent research results. A total of 27,000 cardiac cycles were analyzed for both afore-mentioned signals. The reference value for ejection time was computed based on the T-wave segment duration from the electrocardiogram waveform. In lower blood pressure, which is associated with decreased heart contractility, the results indicated an underestimation of −29 ± 19 ms in ABP and an overestimation of 18 ± 31 ms in PPG. On the other side of the spectrum, during increased contractility, the minimum errors were −3 ± 18 ms and 4 ± 33 ms, respectively. Since the tidal wave feature is strongly affected by arterial tree compliance, the population evaluation results indicate a Pearson’s correlation factor of 0.58 in the ABP case, and 0.53 in PPG. These findings highlight the need for advanced compensation techniques, in particular for PPG assessment, to achieve clinical-grade accuracy.

9 February 2024 in Symmetry
Verified
Journal Article
Open access
PDF file
AVAlexandru Mădălin VIZITIU
Alexandru Mădălin VIZITIU
Lidia DobrescuLidia Dobrescu
Lidia Dobrescu
BTBogdan Catalin Trip
Bogdan Catalin Trip
VBVlad Florian Butnariu
Vlad Florian Butnariu
CMCristian-Constantin Molder
Cristian-Constantin Molder
Simona Viorica HalungaSimona Viorica Halunga
Simona Viorica Halunga
The information technology and communication (IT&C) market consists of computing and telecommunication technology systems, which also include a variety of audio devices. Preserving the confidentiality of transmitted information through these devices stands as a critical concern across various domains and businesses. Notably, spurious electromagnetic emanations emitted by audio devices can be captured and processed, potentially leading to eavesdropping incidents. The evaluation of electronic devices for potential security vulnerabilities often involves employing Transient Electromagnetic Pulse Emanation Standard (TEMPEST) technology. This paper introduces a novel approach to TEMPEST testing specifically tailored for audio devices. The outcomes of the proposed approach offer valuable insights into TEMPEST equipment testing, aiming to mitigate the potential risks posed by threats exploitable by eavesdroppers in everyday scenarios. The present work delves into the examination of two ubiquitous global electronic devices: a notebook and a pair of in-ear headphones. The symmetrical framework of this study arises from the intrinsic similarity that, despite belonging to distinct categories, both devices possess the capability to emit electromagnetic emissions that contain compromised audio signals. This assertion is substantiated by the measurement results presented herein. The proposed methodology involves the analysis of the audio amplitude modulation (AM) demodulated signal in the frequency domain. This innovative approach not only mitigates operator fatigue but also significantly reduces the testing time required for these devices and instrument running hours and leads to the development of new applications.