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ÖgeAnalog neural network based on memristor crossbar arrays(İstanbul Teknik Üniversitesi, 2019) Yıldız, Hacer A. ; Altun, Mustafa ; Güngördü, Doğuş ; Stan, Mircea ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communications EngineeringIn this paper, a new feed forward analog neural network is designed using a memristor based crossbar array architecture. This structure consists of positive and negative polarity connection matrices. In order to show the performance and usefulness of the proposed circuit, it is considered a sample application of iris data recognition. The proposed neural network implementation is approved by the simulation in Cadence design environment using 0.35µm CMOS technology. The results obtained are promising for the implementation of high density neural network.
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ÖgeDefect Tolerant Logic Synthesis for Memristor Crossbars with Performance Evaluation(IEEE, 2018) Tunali, Onur ; Morgül, M. Ceylan ; Altun, Mustafa ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communication EngineeringIn this paper, we study defect-tolerant logic synthesis of memristor-based crossbar architectures. We propose a hybrid algorithm, combining heuristic and exact algorithms, that achieves perfect tolerance for 10-percent stuck-at open defect rates. Along with defect tolerance, we also consider area, delay, and power costs of the memristor crossbars to elaborate on two-level and multi-level logic designs.
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ÖgeA Fast Hill Climbing Algorithm for Defect and Variation Tolerant Logic Mapping of Nano-Crossbar Arrays(IEEE, 2018) Peker, Furkan ; Altun, Mustafa ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communication EngineeringNano-crossbar arrays are area and power efficient structures, generally realized with self-assembly based bottom-up fabrication methods as opposed to relatively costly traditional top-down lithography techniques. This advantage comes with a price: very high process variations. In this work, we focus on the worst-case delay optimization problem in the presence of high process variations. As a variation tolerant logic mapping scheme, a fast hill climbing algorithm is proposed; it offers similar or better delay improvements with much smaller runtimes compared to the methods in the literature. Our algorithm first performs a reducing operation for the crossbar motivated by the fact that the whole crossbar is not necessarily needed for the problem. This significantly decreases the computational load up to 72% percent for benchmark functions. Next, initial column mapping is applied. After the first two steps that can be considered as preparatory, the algorithm proceeds to the last step of hill climbing row search with column reordering where optimization for variation tolerance is performed. As an extension to this work, we directly apply our hill climbing algorithm on defective arrays to perform both defect and variation tolerance. Again, simulation results approve the speed of our algorithm, up to 600 times higher compared to the related algorithms in the literature without sacrificing defect and variation tolerance performance.
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ÖgeA fast logic mapping algorithm for multiple-type-defect tolerance in reconfigurable nano-crossbar arrays(Institute of Electrical and Electronics Engineers (IEEE), 2017-09-21) Tunali, Onur ; Altun, Mustafa ; https://orcid.org/0000-0002-3103-1809 ; Electronics and Communication EngineeringUnlike conventional CMOS circuits, nano-crossbar arrays have considerably high defect rates. Multiple-type defects randomly occur both on crosspoint switches and wires that substantially complicates the design phase of the circuits with an elimination of systematic design choices. In order to overcome this problem, a logic mapping methodology is presented in this paper. A fast heuristic algorithm using pre-mapping logic morphing, defect oriented adaptive sorting, matching with Hadamard multiplication, and backtracking is introduced. The proposed algorithm covers both crosspoint defects including stuck-open and stuck-closed types and wire defects including bridging and broken types. Effects of stuck-closed defects, mostly disregarded in the literature, are studied in depth. In simulations, an industrial benchmark suit is used for obtaining runtime and success rate values of the proposed algorithm in comparison with those of the existing algorithms in the literature. A relative accuracy evaluation is also given in comparison with exact mapping techniques. Finally, the steps of the algorithm that are based on pre-mapping and heuristic matching techniques, are separately justified with experimental results.
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ÖgeIn vivo dielectric properties of healthy and benign rat mammary tissues from 500 MHz to 18 GHz(MDPI, 2020-04) Yılmaz, Tuba ; Ateş Alkan, Fatma ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communication EngineeringThis work investigates the in vivo dielectric properties of healthy and benign rat mammary tissues in an attempt to expand the dielectric property knowledge of animal models. The outcomes of this study can enable testing of microwave medical technologies on animal models and interpretation of tissue alteration-dependent in vivo dielectric properties of mammary tissues. Towards this end, in vivo dielectric properties of healthy rat mammary tissues and chemically induced benign rat mammary tumors including low-grade adenosis, sclerosing adenosis, and adenosis were collected with open-ended coaxial probes from 500 MHz to 18 GHz. The in vivo measurements revealed that the dielectric properties of benign rat mammary tumors are higher than the healthy rat mammary tissues by 9.3% to 35.5% and 19.6% to 48.7% for relative permittivity and conductivity, respectively. Furthermore, to our surprise, we found that the grade of the benign tissue affects the dielectric properties for this study. Finally, a comparison with ex vivo healthy human mammary tissue dielectric properties revealed that the healthy rat mammary tissues best replicate the dielectric properties of healthy medium density human samples.
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ÖgeLogic Synthesis and Testing Techniques for Switching Nano-Crossbar Arrays(Elsevier, 2017) Alexandrescua, Dan ; Altun, Mustafa ; Anghel, Lorena ; Bernasconi, Anna ; Cirianie, Valentina ; Frontini, Luca ; Tahoori, Mehdi ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communication EngineeringBeyond CMOS, new technologies are emerging to extend electronic systems with features unavailable to silicon-based devices. Emerging technologies provide new logic and interconnection structures for computation, storage and communication that may require new design paradigms, and therefore trigger the development of a new generation of design automation tools. In the last decade, several emerging technologies have been proposed and the time has come for studying new ad-hoc techniques and tools for logic synthesis, physical design and testing. The main goal of this project is developing a complete synthesis and optimization methodology for switching nano-crossbar arrays that leads to the design and construction of an emerging nanocomputer. New models for diode, FET, and four-terminal switch based nanoarrays are developed. The proposed methodology implements logic, arithmetic, and memory elements by considering performance parameters such as area, delay, power dissipation, and reliability. With combination of logic, arithmetic, and memory elements a synchronous state machine (SSM), representation of a computer, is realized. The proposed methodology targets variety of emerging technologies including nanowire/nanotube crossbar arrays, magnetic switch-based structures, and crossbar memories. The results of this project will be a foundation of nano-crossbar based circuit design techniques and greatly contribute to the construction of emerging computers beyond CMOS. The topic of this project can be considered under the research area of “Emerging Computing Models” or “Computational Nanoelectronics”, more specifically the design, modeling, and simulation of new nanoscale switches beyond CMOS.
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ÖgeMicrowave dielectric property based classification of renal calculi: Application of a kNN algorithm(Elsevier, 2019) Saçlı, Banu ; Aydınalp, Cemanur ; Cansız, Gökhan ; joof, Sulayman ; Yılmaz, Tuba ; Çayören, Mehmet ; Önal, Bülent ; Akduman, İbrahim ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communication EngineeringThe proper management of renal lithiasis presents a challenge, with the recur- rence rate of the disease being as high as 46%. To prevent recurrence, the first step is the accurate categorization of the discarded renal calculi. Currently, the discarded renal calculi type is determined with the X-ray powder diffraction method which requires a cumbersome sample preparation. This work presents a new approach that can enable fast and accurate classification of discarded renal calculi with minimal sample preparation requirements. To do so, first, the measurements of the dielectric properties of naturally formed renal calculi are collected with the open-ended contact probe technique between 500 MHz to 6 GHz with 100 MHz intervals. Cole–Cole parameters are fitted to the measured dielectric properties with the generalized Newton–Raphson method. The re- nal calculi types are classified based on their Cole–Cole parameters as calcium oxalate, cystine, or struvite. The classification is performed using nearest neigh- bors (kNN) machine learning algorithm with the 10 nearest neighbors, where accuracy as high as 98.17% is achieved.
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ÖgeMicrowave dielectric spectroscopy of renal calculi: A large scale study on dielectric properties from 500 MHz to 18 GHz(IEEE, 2019) Yılmaz, Tuba ; Saçlı, Banu ; Cansız, Gökhan ; joof, Sulayman ; Aydınalp, Cemanur ; Çayören, Mehmet ; Akduman, İbrahim ; Önal, Bülent ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communication EngineeringInherent dielectric property discrepancy between biological anomalies and healthy tissue enables the microwave diagnostic and therapeutic technologies. To reveal this discrepancy, microwave dielectric properties of many different biological tissues are tabulated. Although the dielectric properties of biological tissues are well documented in the literature, the knowledge on microwave dielectric property behavior of the renal calculi is limited. This work presents ultra wideband dielectric properties of three renal calculi types between 500 MHz to 18 GHz to pave the way for possible application of microwave technologies for diagnosis, treatment, and prevention of urolithiasis. Microwave dielectric spectroscopy is performed on a total of 66 natural stone samples with open-ended coaxial probe technique. The samples belong to three commonly diagnosed renal calculi categories, namely calcium oxalate, cystine, struvite. Analysis of variance (ANOVA) test is performed on fitted Cole-Cole parameters and it was concluded that there is a statistically significant difference between the dielectric properties of the renal calculi types. A patient-to-patient statistical test is also performed and it was concluded that there is no statistical difference between the samples belonging to the same renal calculi category. To this end, based on the relative permittivity discrepancy between the renal calculi types, the category of renal calculi can be identified by measuring the dielectric properties of renal calculi with open-ended coaxial probe technique.
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ÖgeMicrowave spectroscopy based classification of rat hepatic tissues: On the significance of dataset(BAJECE, 2020-10) 0000-0003-3052-2945 ; Elektronik ve Haberleşme MühendisliğiWith the advancements in machine learning (ML) algorithms, microwave dielectric spectroscopy emerged as a potential new technology for biological tissue and material categorization. Recent studies reported the successful utilization of dielectric properties and Cole-Cole parameters. However, the role of the dataset was not investigated. Particularly, both dielectric properties and Cole-Cole parameters are derived from the S parameter response. This work investigates the possibility of using S parameters as a dataset to categorize the rat hepatic tissues into cirrhosis, malignant, and healthy categories. Using S parameters can potentially remove the need to derive the dielectric properties and enable the utilization of microwave structures such as narrow or wideband antennas or resonators. To this end, in vivo dielectric properties and S parameters collected from hepatic tissues were classified using logistic regression (LR) and adaptive boosting (AdaBoost) algorithms. Cole-Cole parameters and a reproduced dielectric property data set were also investigated. Data preprocessing is performed by using standardization a principal component analysis (PCA). Using the AdaBoost algorithm over 93% and 88% accuracy is obtained for dielectric properties and S parameters, respectively. These results indicate that the classification can be performed with a 5% accuracy decrease indicating that S parameters can be an alternative dataset for tissue classification.
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ÖgeMulticlass classification of hepatic anomalies with dielectric properties: From phantom materials to rat hepatic tissues(MDPI, 2020-01) Yılmaz, Tuba ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communication EngineeringOpen-ended coaxial probes can be used as tissue characterization devices. However, the technique suffers from a high error rate. To improve this technology, there is a need to decrease the measurement error which is reported to be more than 30% for an in vivo measurement setting. This work investigates the machine learning (ML) algorithms’ ability to decrease the measurement error of open-ended coaxial probe techniques to enable tissue characterization devices. To explore the potential of this technique as a tissue characterization device, performances of multiclass ML algorithms on collected in vivo rat hepatic tissue and phantom dielectric property data were evaluated. Phantoms were used for investigating the potential of proliferating the data set due to difficulty of in vivo data collection from tissues. The dielectric property measurements were collected from 16 rats with hepatic anomalies, 8 rats with healthy hepatic tissues, and in house phantoms. Three ML algorithms, k-nearest neighbors (kNN), logistic regression (LR), and random forests (RF) were used to classify the collected data. The best performance for the classification of hepatic tissues was obtained with 76% accuracy using the LR algorithm. The LR algorithm performed classification with over 98% accuracy within the phantom data and the model generalized to in vivo dielectric property data with 48% accuracy. These findings indicate first, linear models, such as logistic regression, perform better on dielectric property data sets. Second, ML models fitted to the data collected from phantom materials can partly generalize to in vivo dielectric property data due to the discrepancy between dielectric property variability.
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ÖgeNovel methods for efficient realization of logic functions using switching lattices(IEEE Transactions on Computers, 2019) Aksoy, Levent ; Altun, Mustafa ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communications EngineeringTwo-dimensional switching lattices including four-terminal switches are introduced as alternative structures to realize logic functions, aiming to outperform the designs consisting of one-dimensional two-terminal switches. Exact and approximate algorithms have been proposed for the problem of finding a switching lattice which implements a given logic function and has the minimum size,i.e., a minimum number of switches. In this article, we present an approximate algorithm, called JANUS, that explores the search space in a dichotomic search manner. It iteratively checks if the target function can be realized using a given lattice candidate, which is formalized as a satisfiability (SAT) problem. As the lattice size and the number of literals and products in the given target function increase, the size of a SAT problem grows dramatically, increasing the run-time of a SAT solver. To handle the instances that JANUS cannot cope with, we introduce a divide and conquer method called MEDEA. It partitions the target function into smaller sub-functions,finds the realizations of these sub-functions on switching lattices using JANUS, and explores alternative realizations of these sub-functions which may reduce the size of the final lattice. Moreover, we describe the realization of multiple functions in a single lattice. Experimental results show that JANUS can find better solutions than the existing approximate algorithms, even than the exact algorithm which cannot determine a minimum solution in a given time limit. On the other hand, MEDEA can find better solutions on relatively large size instances using a little computational effort when compared to the previously proposed algorithms. Moreover, on instances that the existing methods cannot handle, MEDEA can easily find a solution which is significantly better than the available solutions.
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ÖgeOptimal and Heuristic Algorithms to Synthesize Lattices of Four-Terminal Switches(Elsevier, 2019) Morgul, M. Ceylan ; Altun, Mustafa ; Electronics and Communication Engineering ; Elektronik ve Haberleşme MühendisliğiIn this work, we study implementation of Boolean functions with nano-crossbar arrays where each crosspoint behaves as a fourterminal switch controlled by a Boolean literal. These types of arrays are commonly called as switching lattices. We propose optimal and heuristic algorithms that minimize lattice sizes to implement a given Boolean function. The algorithms are mainly constructed on a technique that finds Boolean functions of lattices having independent inputs. This technique works recursively by using transition matrices representing columns and rows of the lattice. It performs symbolic manipulation of Boolean literals as opposed to using truth tables that allows us to successfully find Boolean functions having up to 81 variables corresponding to a 9×9-lattice. With a Boolean function of a certain sized lattice, we check if a given function can be implemented with this lattice size by defining the problem as a satisfiability problem. This process is repeated until a desired solution is found. Additionally, we fix the previously proposed algorithm that is claimed to be optimal. The fixed version guarantees optimal sizes. Finally, we perform synthesis trials on standard benchmark circuits to evaluate the proposed algorithms by considering lattice sizes and runtimes in comparison with the recently proposed three algorithms.
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ÖgePermanent and transient fault tolerance for reconfigurable nano-crossbar arrays( 2016-08-25) Tunali, Onur ; Altun, Mustafa ; https://orcid.org/0000-0002-3103-1809 ; Department of Nanoscience and Nanoengineering ; Department of Electronics and Communication EngineeringThis paper studies fault tolerance in switching reconfigurable nano-crossbar arrays. Both permanent and transient faults are taken into account by independently assigning stuck-open and stuck-closed fault probabilities into crosspoints. In the presence of permanent faults, a fast and accurate heuristic algorithm is proposed that uses the techniques of index sorting, backtracking, and row matching. The algorithm's effectiveness is demonstrated on standard benchmark circuits in terms of runtime, success rate, and accuracy. In the presence of transient faults, tolerance analysis is performed by formally and recursively determining tolerable fault positions. In this way, we are able to specify fault tolerance performances of nano-crossbars without relying on randomly generated faults that is relatively costly regarding that the number of fault distributions in a crossbar grows exponentially with the crossbar size.
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ÖgeRadio-frequency and microwave techniques for non-invasive measurement of blood glucose levels(MDPI, 2019) Yılmaz, Tuba ; Foster, Robert ; Hao, Yang ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communication EngineeringThis paper reviews non-invasive blood glucose measurements via dielectric spectroscopy at microwave frequencies presented in the literature. The intent is to clarify the key challenges that must be overcome if this approach is to work, to suggest some possible ways towards addressing these challenges and to contribute towards prevention of unnecessary ‘reinvention of the wheel’.
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ÖgeSensing Schemes for STT-MRAMs structured with high TMR in low RA MTJs(Elsevier, 2019) Atasoyu, Mesut ; Altun, Mustafa ; Ozoguz, Serdar ; Elektronik ve Haberleşme Mühendisliği ; Electronics and Communication EngineeringIn this work, we investigated the sensing challenges of spin-transfer torque MRAMs structured with perpendicular magnetic tunnel junctions with a high tunneling magnetoresistance ratio in a low resistance-area product. To overcome the problems of reading this type of memory, we have proposed a voltage sensing amplifier topology and compared its performance to that of the current sensing amplifier in terms of power, speed, and bit error rate performance. We have verified that the proposed sensing scheme offers a substantial improvement in bit-error-rate performance. To enumerate the read operations of the proposed sensing scheme with the proposed cross-coupled capacitive feedback technique on the clamped circuity have successfully been performed a 2.5X reduction in average low power and a 13X increase in average reading speed compared with the previous works due to its device structure and the proposed circuit technique.
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ÖgeA survey of fault-tolerance algorithms for reconfigurable nano-crossbar arrays(Association for Computing Machinery (ACM), 2017-01-05) Tunalı, Onur ; Altun, Mustafa ; https://orcid.org/0000-0002-3103-1809 ; Electronics and Communication EngineeringNano-crossbar arrays have emerged as a promising and viable technology to improve computing performance of electronic circuits beyond the limits of current CMOS. Arrays offer both structural efficiency with reconfiguration and prospective capability of integration with different technologies. However, certain problems need to be addressed, and the most important one is the prevailing occurrence of faults. Considering fault rate projections as high as 20% that is much higher than those of CMOS, it is fair to expect sophisticated fault-tolerance methods. The focus of this survey article is the assessment and evaluation of these methods and related algorithms applied in logic mapping and configuration processes. As a start, we concisely explain reconfigurable nano-crossbar arrays with their fault characteristics and models. Following that, we demonstrate configuration techniques of the arrays in the presence of permanent faults and elaborate on two main fault-tolerance methodologies, namely defect-unaware and defect-aware approaches, with a short review on advantages and disadvantages. For both methodologies, we present detailed experimental results of related algorithms regarding their strengths and weaknesses with a comprehensive yield, success rate and runtime analysis. Next, we overview fault-tolerance approaches for transient faults. As a conclusion, we overview the proposed algorithms with future directions and upcoming challenges.