AUT Journal of Electrical Engineering
https://eej.aut.ac.ir/
AUT Journal of Electrical Engineeringendaily1Thu, 01 Dec 2022 00:00:00 +0330Thu, 01 Dec 2022 00:00:00 +0330Advances on CMOS Folded-Cascode Operational Transconductance Amplifier: A Tutorial Review
https://eej.aut.ac.ir/article_4905.html
In this paper, a tutorial review on several structural improvements of the CMOS folded-cascode operational transconductance amplifier (OTA) is presented. After a brief discussion on the structure and operation of the conventional folded-cascode amplifier, its several architectural improvements are reviewed. These improvements include advances on class A and class AB folded-cascode amplifiers and recycling folded-cascode amplifier. Then, several improved class A and class AB recycling folded-cascode operational transconductance amplifiers are discussed and finally some two-stage operational transconductance amplifiers based on the current recycling technique are reviewed. As it is seen, many architectural innovations have been proposed to improve both small-signal parameters including DC gain, unity-gain bandwidth, and phase margin, and large-signal operation, which is usually characterized by slew rate, in the proposed OTAs compared to the basic folded-cascode amplifier. Current recycling, shunt current sources, cross-coupled transistors to realize local positive feedback paths, local common-mode feedback, flipped voltage follower cells to realize the class AB operation, active current mirrors, and several other techniques have been utilized in the structural improvements of the basic folded-cascode operational transconductance amplifier. The achieved results are more promising and demonstrate substantial achievements in design of operational transconductance amplifiers in low-voltage and more scaled nano-meter CMOS processes.A Wideband Transmitarray Antenna Design Based on The Transmission Characteristic of Unit Cell
https://eej.aut.ac.ir/article_4987.html
In this paper a procedure is proposed to design a wideband transmitarray upon a specified frequency band. In this way, phase control parameter of unit cell is adjusted in a suggested range ensuring linear phase change and low transmission loss over the band. The unit cell is designed, for a range of phase control parameter (e.g. slot length in a CSRR) in which, 360&deg; phase variation is provided. Part of this range is applied for the central elements of TA, in which the maximum overlapped passband (for different values of phase control parameter) around the desired frequency to be achieved. In this way, a scenario for the phase specification of the array elements would be obtained. This range is specially applied for the central elements of the array which are in exposure of feed peak power. As a proof of concept, an 14&times;14 elements transmitarray is designed and fabricated based on a back to back square complementary split ring resonator (CSRR). Measurement results indicate maximum gain, 1-dB bandwidth and aperture efficiency of 24.6 dB, 18.4% and 53% respectively at the center frequency of 11.5GHz. At the end of the paper, a comparison between proposed TA and the previous ones is provided.Optical Sensors for Industrial and Biomedical Applications
https://eej.aut.ac.ir/article_4835.html
The article begins with a brief review of those industrial and biomedical optical sensors which have been designed and fabricated in Photonics Research Laboratory, School of Electrical and Computer Engineering, University of Tehran. Firstly, development of a fiber-based fluid temperature and pressure sensing system is described. We describe fabrication procedure for the designed temperature and pressure sensors and elaborate on the interrogating electronic system for processing the sensor signals. Then, a frequency-modulation interferometric sensor enabling low-cost and highly sensitive refractive index measurement is presented. The sensor utilizes a setup based on free-space optics. Having introduced the first categories of sensors, we briefly describe transmission-line formulation (TLF) method which has been developed in our research group for the diffraction analysis of optical periodic structures. Application of this method to the design of a coupled cross-stacked guided-mode resonance sensor with a high surface sensitivity is demonstrated. We further review the design of dual-resonance nanostructured plasmonic sensors that can be used to differentiate background refractive index variation from adsorption of a layer on the sensing surface, and to estimate the thickness of adsorbed layers. Finally, we use the TLF method to design a spectrometer-free configuration for a dual-mode plasmonic sensor, which substantially simplifies the measurement setup.Retracted Article: "A Multi-Stage TIA based on Cascoded-Inverter Structures for Low-power Applications"
https://eej.aut.ac.ir/article_4724.html
This article discusses a multi-stage transimpedance amplifier (known as TIA), which is based on three stages of a modified inverter structure. The traditional inverter structures&rsquo; performances are improved adding two cascoded transistors. This new structure benefits from elimination of the Miller-capacitances in comparison with the traditional inverters, which can provide higher speed and wider frequency bandwidth. Manipulating the trade-offs among bandwidth, gain and power consumption beside using Gm/ID technique, this paper introduces a low-power transimpedance amplifier for high-bit rates in optical communication receiver systems. Moreover, active types of inductors are also used to lesson the occupied area and increase the frequency bandwidth. Transferring poles of the improved circuit to higher frequencies means less required DC current for a fixed bandwidth range, which results in low-power characteristic. The proposed circuit is simulated using 90nm CMOS technology parameters. Results for frequency response show the transimpedance gain of 42.3 dBâ„¦ and the bandwidth of 3.47 GHz. Moreover, the circuit consumes 2.7mW using 1V supply, which is relatively close to the targeted 2.5mW power, using gm/ID. Other required simulations such as eye diagram, Monte Carlo, temperature and VDD variations, post layout simulation beside its mathematical equations are also added to manuscript to justify ts performance.Single-ended 6T SRAM cell with low power/energy consumption and high stability
https://eej.aut.ac.ir/article_4693.html
In this work, we propose 6T cell with single-ended characteristics to achieve improved stability, decrease energy consumption and decrease leakage power. The cell is compared with strong 10 and 12 transistor structures with good and excellent specifications. However, the above structure is designed to have the best parameters with low size and a minimum number of transistors that reduce the size of the cell. In some parameters, such as the write noise margin, in comparison with other structures, the structure has the best merits, even higher than the structures of 12 and 10 transistors. The write operation is enhanced by cutting the pull-down path to the storage node to be written &ldquo;1&rdquo;; the read operation is performed without cutting the pull-down path. At VDD=0.4V, the static power, read margin, write margin, read energy, and write energy of the proposed structure are superior by 33%, 50%, 215%, 9%, and 5%, respectively, in contrast with the traditional 6T. The Electrical quality metric (EQM) parameter has been improved about ten times compared with the standard 6T structure, showing that the value of the new structure has been introduced. A Monte Carlo simulation of 5,000 read and write yields in the 32nm technology revealed that our cell has a 2x and 3.4x higher yield than the typical 6T cell. Consequently, the proposed 6T is an appropriate option for applications requiring low energy and high robustness.Gradient-Controled Gaussian Kernel for Image Inpainting
https://eej.aut.ac.ir/article_4873.html
Image inpainting is the process of filling in damaged or missing regions in an image by using information from known regions or known pixels of the image. One of the most important techniques for inpainting is convolution based methods in which a kernel is convolved with the damaged image iteratively. Convolution based algorithms are very quick but they don&#039;t have good results in structures and textural regions and result in blurring. The kernel size in the convolution based algorithm is a critical parameter. The large size results in edge blurring and if the kernel size is small, the information may not be sufficient for reconstruction. In this paper, a novel convolution based algorithm is proposed that uses known pixels&#039; gradient to construct a convolution mask. In this algorithm, the kernel size is controlled by the gradient of the image in the known regions. The algorithm computes the weighted sum of the known pixels in a neighborhood around a damaged pixel and replaces the value in the place of that damaged pixel. The proposed algorithm is fast and results in good edges and smooth regions reconstruction. It is an iterative algorithm and implementation of this is very simple. Experimental results show the effectiveness of our algorithm.Design and Simulation of Pseudo Ternary Adder based on CNTFET
https://eej.aut.ac.ir/article_4764.html
Utilizing multiple logic instead of binary logic levels makes the same system to be realized with reduced number of internal connections and wiring, occupying smaller chip area while achieving higher operational speed. Due to the unique features nanotubes carbon tubes field effect transistors, as well as the possibility of designing different threshold voltages for transistors, designing multi-level logic systems is much simpler and less costly. Therefore, considering that the existing processing systems work on a dual basis, the design of binary to ternary converters and vice versa is very important and basic processing systems. In spite of all advantages mentioned, the multilevel logic systems relay on voltage dividing mechanism to provide suitable mid-voltage outputs. This, however, requires a direct current flow from supply voltage to the ground making the structure power hungry. Eliminating the mid-voltage outputs can help the structure to resemble binary design approach and be more power efficient as discussed in this paper. In this paper, pseudo ternary addition blocks, namely a half-adder, a full-adder block are designed and implemented based on CNTFET which try to eliminate '1' output for mid-stages wherever possible. The proposed adders are implemented, simulated and verified in HSPICE software using 32nm CNTFET technology. The simulation results reveal the proposed pseudo ternary full-adder block consumes just 1.037 &mu;W power and has the propagation delay of 290 ps.Design Procedure for a Novel LMDS Base Station Reflectarray Antenna
https://eej.aut.ac.ir/article_4903.html
A reflectarray antenna is designed to operate at X-band as a Local Multipoint Distribution Service (LMDS) base station antenna. It is a center-fed single layer reflectarray consisting of 23&times;27 elements. The unit cell of the reflectarray has linear polarization with more than 400&deg; linear phase shift and its geometrical parameters have been optimized to achieve wide bandwidth and low cross polarization (XP) level for the reflectarray. An iterative design procedure, that is valid for obtaining any arbitrary pattern, has been implemented to achieve the specified radiation pattern over a desired frequency range. The method has been successfully applied to a LMDS base station antenna, characterized by a sectorial cosecant squared beam in the frequency range of 9.3 GHz - 11.5 GHz. The simulation results are in a good agreement with the design requirements. The antenna has cosecant squared pattern over the bandwidth of 21%, XP level better than -30 dB, and SLL less than -20 dB in both elevation and azimuth planes. The total size of the 23&times;27-element array is 246&times;289 mm2 and its 1dB gain bandwidth is wider than 19%. The proposed antenna performs significantly better than similar structures and has all the features and standards required for LMDS base station antenna.Studying the Role of Ion Migration on Perovskite Light-Emitting Diodes by Steady-State approach
https://eej.aut.ac.ir/article_4771.html
Despite the rapid development of perovskite-based light-emitting diodes (PeLEDs) within the last decade, the role of ion migration on the devices' operation has not been completely understood. It is considered the most complicated and mysterious process, affecting PeLED's operation. On one hand, it is widely accepted that the ion migration, as an intrinsic phenomenon, is one of the main origins for PeLEDs' low stability and on the other hand, the defect passivation caused by mobile ions gives rise to enhanced charge injection from the electron and hole transporting layers, leading to the more efficient light-emitting diodes. Therefore, it is critical to have a comprehensive insight into the underlying principles of ion migration and its contributing factors. In this paper, the ion migration phenomenon and its influence on the operation of a PeLED are surveyed using the Finite Element Method (FEM) simulation. The accumulation of anions and cations at the hole and electron transporting layer's interfaces with the perovskite facilitates hole and electron injection, respectively, which results in more carrier density favoring the radiative recombination. Thereupon, ion migration is a phenomenon that is closely related to the device's operation and stability, by controlling which a more stable PeLED is attainable. Our results provide a better understanding of the physics behind the ion migration which is the first step for designing more efficient devices.A Fast Fault Location Based on a New Proposed Modern Metaheuristic Optimization Algorithm
https://eej.aut.ac.ir/article_4912.html
Double-circuit power systems are one of the main types of modern transmission lines because of their reliability. Fault location in these transmission lines has always been a potential problem due to the mutual coupling between lines. Accordingly, this paper presents a novel objective function for the fault location using synchronous post-fault measurements of currents and voltages captured by distance protective relays. Moreover, a fast and accurate modern metaheuristic optimization algorithm for this cost function is proposed, which are key parameters to estimate the fault location methods based on optimization algorithms. In this regard, first, the input data (current and voltage signals) were refined using some auxiliary functions such as fast Fourier transformation (FFT), decaying dc elimination (DDE), and frequency tracking algorithm to accurately extract the fundamental component of the voltage and current signals. Then, the proposed fault location based on the proposed metaheuristic optimization algorithm estimates the fault location using these input signals. The main advantage of the presented algorithm is parallel estimation processing to improve the convergence speed and the accuracy of the objective function of the fault location. To validate the performance of the proposed approach, it was applied to various fault types and various operating conditions. In addition, the performance of the proposed method was compared with different fault location methods. The simulation was implemented in the PSCAD and MATLAB&reg; software. The simulation results show that the novel proposed approach outperforms other fault locations in estimating the fault location.Transient Analysis of Donor-like Surface Traps in GaN HEMTs
https://eej.aut.ac.ir/article_4770.html
Charge trapping in Gallium Nitride based devices affect their reliability and performance. In this work we study the dynamics of charge capture and emission in donor-like surface traps and the impact of trapped charges on transient response of the drain current in Gallium Nitride High Electron Mobility Transistors (GaN HEMTs). To simulate transient characteristics, traps are excited into their empty or filled state by applying initial pulse on gate (gate-lag technique) or on drain (drain-lag) and then the drain current is monitored during transition toward steady state condition. The results show up to 44% variation in drain current level, which reflects the importance of trapped charges in the device characteristics. The effect of physical parameters, including trap energy level and temperature have been characterized using gate and drain-lag. A simple physical model is proposed (based on the Arrhenius relation) and calibrated with simulation results to obtain the emission and capture time-constants. The results extracted from the physical model show that the time constant for capture and emission varies from few microseconds up to few seconds depending on temperature and trap energy level and the result are in good agreement with TCAD simulations. This is an important step toward incorporation of charge trapping effect into the charge-based compact model of GaN HEMTs.Classifying the Clarity of Questions in CQA Networks: A Topic based Approach
https://eej.aut.ac.ir/article_4927.html
Today, there are various sources of information in different fields that users can refer to. Generally, the presence of a question in users&#039; minds leads to reference to these sources of information. Users can search for the answer by entering a few keywords in search engines. They can also ask their questions in more detail in the Community Question Answering networks (CQA) so that experts can give a more comprehensive answer to their questions. To get the proper answer, it is necessary to address all the required details in the question. The questions posted in these networks can be divided into clear and unclear questions. In this study, an attempt has been made to extract unique features from the questions through various machine learning approaches, which can be used to classify questions. To extract these features, the word vector of each question was created, and then, using unsupervised algorithms, the questions with similar word vectors were placed in the same group. Then, repetitive concepts were extracted from each group, and their repetition rate in each question makes its feature vector. Finally, the questions were classified based on the extracted feature vector, using ensemble classification models. The achievement of this study is an efficient classification model along with efficient high-resolution feature extraction for classifying clear and unclear questions in CQA networks. Compared to other baselines and transformer-based models on different datasets, the proposed method makes high accuracy results.An Active Pixel Sensor with Built-in a Unity Gain Buffer
https://eej.aut.ac.ir/article_4773.html
This paper presents an active pixel sensor (APS) with a built-in readout circuit. A unity-gain buffer as a pixel readout circuit is used to read the signals of four adjacent pixels. Compared with the conventional four-transistor APS (4T-APS) which is connected to a CMOS source-follower readout circuit, the introduced circuit has higher accuracy, higher linearity, and fewer transistors. Due to the high linearity and accuracy of the pixel readout circuit, the proposed method can help to improve the final image quality of the sensor. For a fair comparison between the conventional 4T-APS (with source-follower readout circuit) and the proposed circuit, both circuits are designed with the same power consumption. Simulation results show that the proposed circuit is 16% more accurate, 11% higher fill factor, and 10 dB more linear than the conventional circuit. The total power consumption of the proposed circuit with a built-in buffer is almost 17 &micro;W with a 1.8 V power supply and its layout size is 14.8&micro;m&times;14.8&micro;m. The total number of transistors used in this method to read the signals of four pinned-photodiodes is 11, whereas, in the conventional method, 16 transistors are required under the same circumstances. The proposed circuit is designed in 0.18&micro;m CMOS technology.Control Strategy for Input-Parallel and Output-Parallel Connected DC-DC Converters
https://eej.aut.ac.ir/article_4932.html
Input-Parallel Output-Parallel DC-DC converters are convenient for high voltage and high current applications. One important goal this type of connection is to power-sharing and reduce circulating current between the converters. Therefore, control methods for power-sharing between converters should be used when the parameters mismatch. In this paper, a configuration comprising two DC-DC common grounded Z-source converters with input-parallel output-parallel connections is presented, which common grounded Z-source converter have advantages over similar converters. This study proposes two control strategies: (1) a decentralized inverse-droop control, (2) a general control strategy. Inverse-droop control is a simple method and does not need any communication between parallel converters. In the general control strategy, each converter is self-contained, and no external controller is required for achieving input/output current sharing, and a few wires are needed to create the entire system. The simulation results of an Input-Parallel Output-Parallel system comprising two common grounded Z-source converters are evaluated for investigating effectiveness of general control and inverse-droop control. It reported performance of the general control method to be better than the decentralized inverse-droop control method, which enhances the stability and dynamic characteristics of the system. The validity of the two control strategies has been studied through MATLAB simulation and the results got satisfactorilyDiagnosing cancerous tumor by two techniques: photoacoustic imaging and thermoacoustic tomography with electric excitationâ€”a numerical approach for comparison
https://eej.aut.ac.ir/article_4813.html
A numerical study and simulation of cancerous tumor detection using the photoacoustic (PA) phenomenon and thermoacoustic with electric excitation (TATE) are presented. This report was in a small dimension of mimic breast tissue. Besides, the different layers of the breast were considered. The optical, thermal, elastic, electric, and acoustic characteristics of different layers of breast tissue and tumor at radiated laser wavelength (800 nm) and electric voltage pulse, were accurately calculated or obtained from reliable sources for the calculations to be done accurately and realistically; also, for accurate comparing of two methods, the amount and power of voltage and laser have been selected as the minimum allowable values. Therefore, it was possible to rely on the values and characteristics of the resulting data in comparing the accuracy and clarification of the two methods. A single suitable platform for simulating, which is commercially available Finite Element software (COMSOL&reg;), has been selected. By using this platform, we were able to simulate these two methods from stimulation to propagation continuously. Finally, by studying the data matrix of two simulations, we can demonstrate the maximum difference of stress in and out of tumor in the two methods is about 0.1 Pa higher in PAT relative to the TATE. It means PAT is more accurate than TATE and the combination of these two methods can be ideal for the accurate and complete study of cancerous tumors.The effectiveness of non-ionizing radiation protective clothing: A computational study
https://eej.aut.ac.ir/article_4950.html
Exposure protective clothing has been suggested especially for pregnant women as a protection against RF and microwave electromagnetic fields. These are usually made of metal-woven fabrics. In this article, we use computer simulation methods with a homogeneous human model and plane wave exposure at different polarizations and wave incidence angles over a wide range of frequencies, to inspect if a typical anti-exposure clothing model might fail to reduce the fields inside the body under certain exposure conditions and/or at some frequencies. Indeed, as far as our model and computational study can represent actual conditions, it is found that for waves incident along the body axis (as arises e.g. in the sleeping status) the clothing might not only fail to reduce the penetration of EM fields, but can rather increase the electric field intensity in certain body areas, including the abdominal parts which were intended to be protected during pregnancy. The increase can be as high as 30 dB as compared with the same scenario without radiation protective clothing, and is more pronounced for frequencies above 10 MHz. We conclude that more physics-aware designs should be employed for such clothing, and simple intuitive designs shall be checked prior to production and marketing.Assistive Control of a Hip Exoskeleton Robot, using a DQN-Adjusted Delayed Output Feedback Method
https://eej.aut.ac.ir/article_4969.html
A major challenge in the development of an assistive exoskeleton robot is to design appropriate control algorithms. For these algorithms to work in any intended motion and to be easily implementable, they should be trajectory-independent and should require a minimum number of sensors. As a simple assistive strategy with all of these promising features, delayed output feedback control (DOFC) is shown to be effective in assisting the wearers in different types of motion. In this method, the assistive torques are defined in proportion to delayed feedback from the angle difference between the two legs. The authors have recently suggested an intelligent version of DOFC in which a Deep Q-Network (DQN) was used to adjust the feedback delay according to the speed of the motion. Simulation studies were used to investigate of the idea. By conducting some real-world experiments, the present paper extends the results to practical conditions. The provided results clearly verify that if the time delay is adjusted according to the walking speed, the DOFC method can effectively help the users in their motions of any speed. The results also indicated that a fixed or an inappropriate value of the delay may result in resistance against the user motion.GPR of Multiple Vertical Rods under Lightning Strokes Considering Ionization, Dispersion, and Non-Homogeneity of Lossy Soils
https://eej.aut.ac.ir/article_4978.html
In this paper, different aspects of lossy soils including ionization, and frequency-dependence of electrical parameters of soils (dispersive soil) simultaneously on the grounding potential rise (GPR) of multiple vertical rods under lightning return strokes are investigated. In all analyses, an efficient modeling approach called improved multi-conductor transmission line (IMTL) is adopted. Based on the previously published papers, this modeling approach is in good agreement with full-wave methods.
In the case of single rod, IMTL-based numerical analyses show that when the two mentioned aspects, i.e., ionization and dispersion, are simultaneously,occurred, GPR is more decreased with respect to situations where only one aspect , i.e., either ionization or dispersion, is considered. This reduction is more pronounced for highly resistive soils, and fast-fronted lightning currents. In the case of multiple rods, however, it is placed between the GPRs of only-ionized and only-dispersive soils. Moreover, sensitivity analysis on the non-homogeneity effect in ionized and dispersive soils is carried out.
Since, the measurement of GPR at high frequencies is difficult, this motivates the authors to propose closed-form expressions for GPR of multiple rods. Hence, comprehensively predicting formulae for GPR of multiple rods versus parameters of lightning current, lossy soil and rod length are extracted. The predicted results are in excellent agreement with IMTL.