Αντικείμενο της παρούσας Ειδικής Επιστημονικής Εργασίας είναι η ανάπτυξη φίλτρων στο πεδίο της τετραγωνικής ρίζας με τη μέθοδο του γραμμικού μετασχηματισμού (Linear Transformation). Ως παράδειγμα, δίνεται η σχεδίαση, η εξομοίωση και τέλος η φυσική σχεδίαση ενός ελλειπτικού βαθυπερατού φίλτρου 3ης τάξης στο πεδίο της τετραγωνικής ρίζας (Square-Root Domain). Για λόγους σύγκρισης, η σχεδίαση του φίλτρου γίνεται με τέσσερις διαφορετικές μεθόδους εξομοίωσης παθητικών φίλτρων (Leapfrog, Topologic, Wave και Linear Trasformation method) και η ανάλυση κάθε μεθόδου παρουσιάζεται σε αντίστοιχο κεφάλαιο. / The subject of this master thesis is the design of analog filters in square root domain utilizing the method of Linear Transformation. As a design example a third order elliptic lowpass filter transfer function will be realized. For comparison results we are using four different design methods (Leapfrog, Topologic, Wave and Linear Trasformation)in order to realize such filter. Each synthesis method is demonstrated in different chapter.

Translinear circuits are circuits in which the exponential relationship between the output current and input voltage of a circuit element is exploited to realize various algebraic or differential equations. This thesis is concerned with a subclass of translinear circuits, in which the basic translinear element, called a multiple-input translinear element (MITE), has an output current that is exponentially related to a weighted sum of its input voltages. MITE networks can be used for the implementation of the same class of functions as traditional translinear circuits. The implementation of algebraic or (algebraic) differential equations using MITEs can be reduced to the implementation of the product-of-power-law (POPL) relationships, in which an output is given by the product of inputs raised to different powers. Hence, the synthesis of POPL relationships, and their optimization with respect to the relevant cost functions, is very important in the theory of MITE networks. In this thesis, different constraints on the topology of POPL networks that result in desirable system behavior are explored and different methods of synthesis, subject to these constraints, are developed. The constraints are usually conditions on certain matrices of the network, which characterize the weights in the relevant MITEs. Some of these constraints are related to the uniqueness of the operating point of the network and the stability of the network. Conditions that satisfy these constraints are developed in this work. The cost functions to be minimized are the number of MITEs and the number of input gates in each MITE. A complete solution to POPL network synthesis is presented here that minimizes the number of MITEs first and then minimizes the number of input gates to each MITE. A procedure for synthesizing POPL relationships optimally when the number of gates is minimal, i.e., 2, has also been developed here for the single--output case. A MITE structure that produces the maximum number of functions with minimal reconfigurability is developed for use in MITE field--programmable analog arrays. The extension of these constraints to the synthesis of linear filters is also explored, the constraint here being that the filter network should have a unique operating point in the presence of nonidealities. Synthesis examples presented here include nonlinear functions like the arctangent and the gaussian function which find application in analog implementations of particle filters. Synthesis of dynamical systems is presented here using the examples of a Lorenz system and a sinusoidal oscillator. The procedures developed here provide a structured way to automate the synthesis of nonlinear algebraic functions and differential equations using MITEs.

Αντικείμενο της διπλωματικής εργασίας είναι η σχεδίαση ενός βιοϊατρικού συστήματος που είναι κατάλληλο για την ανίχνευση εμβοών σε ασθενείς. Το σύστημα αυτό αποτελείται από ένα αναλογικό τμήμα το οποίο περιλαμβάνει τους εξαγωγείς ενέργειας ζώνης συχνοτήτων για τα alpha, gamma και theta waves του εγκεφάλου που τροφοδοτούν τα αντίστοιχα κανάλια του συστήματος. Επίσης, το σύστημα περιλαμβάνει και ένα ψηφιακό τμήμα αποτελούμενο από συγκριτές ρεύματος και μια πύλη AND και το οποίο θα χρησιμεύσει για την λήψη της απόφασης σχετικά με το αν πάσχει ή όχι ο ασθενής. Η έξοδος του συστήματος θα οδηγεί ένα σύστημα ανάδρασης, ο οποίος θα προσαρμόζει τα επίπεδα έντασης των αντίστοιχων σημάτων που δέχεται ο ασθενής για την αποφυγή της εμφάνισης του φαινομένου της εμβοής. Η υλοποίηση του συστήματος γίνεται με χρήση MOS transistors τα οποία λειτουργούν στην περιοχή υποκατωφλίου. Η χρήση μικρών ρευμάτων πόλωσης δίνει τη δυνατότητα για σχεδίαση συστημάτων με χαμηλή κατανάλωση ισχύος και ταυτόχρονα επιτρέπει την υλοποίηση μεγάλων τιμών αντιστάσεων, οι οποίες είναι απαραίτητες για την πραγματοποίηση μεγάλων σταθερών χρόνου που απαιτούνται για τη διαχείριση των χαμηλής συχνότητας βιοϊατρικών σημάτων. Στόχος της διπλωματικής εργασίας είναι η ανάπτυξη πρωτότυπης τοπολογίας για το αναλογικό τμήμα του συστήματος. Αυτό επιτεύχθηκε με την ανάπτυξη νέων δομών φίλτρων τα οποία λειτουργούν στο πεδίο του υπερβολικού ημιτόνου. Οι κύριοι λόγοι υιοθέτησης αυτής της τεχνικής είναι ότι προσφέρει ταυτόχρονα τα παρακάτω: (α) δυνατότητα επεξεργασίας σημάτων τα οποία είναι μεγαλύτερα από το ρεύμα πόλωσης, λόγω της ενσωματωμένης λειτουργίας σε τάξη-ΑΒ, (β) δυνατότητα λειτουργίας με καλή γραμμικότητα σε πολύ χαμηλή τάση τροφοδοσίας, (γ) ηλεκτρονική ρύθμιση των συχνοτικών χαρακτηριστικών τους από το ρεύμα πόλωσης, (δ) υλοποίηση φίλτρων χωρίς αντιστάτες, (ε) υλοποίηση φίλτρων με χρήση μόνο γειωμένων πυκνωτών. Η σχεδίαση των κυκλωμάτων, τόσο σε επίπεδο σχηματικού, όσο και σε επίπεδο μασκών, έγινε με τη χρήση του λογισμικού Cadence και με το Design Kit που παρέχεται από την τεχνολογία AMS CMOS C35 0.35μm. Συγκρινόμενη με την αντίστοιχη ήδη προταθείσα δομή ανιχνευτή εμβοών, η προτεινόμενη τοπολογία προσφέρει τα παρακάτω ελκυστικά χαρακτηριστικά: (α) μειωμένη κατανάλωση ισχύος και (β) λειτουργία του αναλογικού τμήματος σε μικρότερη τάση τροφοδοσίας (0.5V). / Subject of this M. Sc.Τhesis is the design of a biomedical system that is suitable for detecting tinnitus in patients. This system consists of an analog subsystem comprising band energy extractors for alpha, gamma and theta waves of the EEG that feed the channels of the system. The system also includes a digital section composed of current comparator and AND gate, which will serve as a decision on whether or not the suffering patient. The output of the system will drive a feedback system, which will adjust the intensity levels of the respective signals received by the patient to prevent the occurrence of the phenomenon of tinnitus. The system implementation is done using MOS transistors operating in the subthreshold region. The use of low-level bias currents allows for system design with low power consumption and, simultaneously, enables the implementation of large values of resistors that are necessary for the realization of large time constants required for the handling of low frequency biomedical signals. The aim of this thesis is to develop novel topology for the analog subsystem. Tjhis was achieved through the development ddevelopment of novel structures of filters using the concept of filtering in the Sinh-Domain. The main reasons for using this technique is that it simultaneously offers the following attractive characteristics: (a) capability for processing signals which are larger than the bias current, due to the inherent class-AB operation, (b) ability to achieve a relative high linearity at very low power supply voltage, (c) electronic adjustment of frequency characteristics through the bias current, (d) implementation of filters without resistors, and (e) implementation of filters using only grounded capacitors. The design of circuits, both at schematic and post-layout levels was performed using the Cadence software and the Design Kit provided by the AMS CMOS C35 0.35μm technology. Compared with the corresponding already proposed structure tinnitus detector, the proposed topology to offer the following attractive features: (a) reduced power consumption, and (b) operation of the analog section in lower supply voltage (0.5V).

Οι ηλεκτρονικοί αρμονικοί ταλαντωτές είναι βαθμίδες με ευρεία εφαρμογή σε τηλεπικοινωνιακά συστήματα, σε συστήματα επεξεργασίας σήματος και σε ηλεκτρονικά ισχύος. Στην εργασία αυτή, προτείνεται μια νέα γενική τοπολογία ταλαντωτή πολλαπλών φάσεων, η οποία λειτουργεί στο πεδίο του υπερβολικού ημιτόνου. Κύρια πλεονεκτήματα είναι η δυνατότητα λειτουργίας σε περιβάλλον χαμηλής τάσης τροφοδοσίας και η ηλεκτρονική ρύθμιση της συμπεριφοράς του ταλαντωτή. Ως παράδειγμα σχεδίασης δίνεται ένας αρμονικός ταλαντωτής πολλαπλών φάσεων εξόδου 3ης/6ης τάξης, που η εξομοίωση της λειτουργίας του έγινε με τη χρήση του λογισμικού Analog Design Environment της Cadence. / Electronic harmonic oscillators are stages with wide application in telecommunication systems, in signal processing systems and power electronics. In this project, a new multiphase oscillator topology is proposed, designed to operate in sinh domain. Main advantages are the ability to operate at low voltage and the electronic tuning of the oscillator’s behavior. A multiphase sinusoidal oscillator, 3rd/6th order, is given as an example. The validity of the proposed methods is verified through simulation results using the Cadence Analog Design Environment software.

<p>The last few decades have witnessed unprecedented growth in multiple areas of electronics spanning low-power sensing, intelligent computing and high-speed wireless connectivity. In the foreseeable future, there would be hundreds of billions of computing devices, sensors, things and people, wherein the technology will become intertwined with our lives through continuous interaction and collaboration between humans and machines. Such human-centric ideas give rise to the concept of internet of bodies (IoB), which calls for novel and energy-efficient techniques for sensing, processing and secure communication for resource-constrained IoB nodes.As we have painfully learnt during the pandemic, point-of-care diagnostics along with continuous sensing and long-term connectivity has become one of the major requirements in the healthcare industry, further emphasizing the need for energy-efficiency and security in the resource-constrained devices around us.</p> <p>  </p> <p>  With this vision in mind, I’ll divide this dissertation into the following chapters. The first part (Chapter 2) will cover time-domain sensing techniques which allow inherent energy-resolution scalability, and will show the fundamental limits of achievable resolution. Implementations will include 1) a radiation sensing system for occupational dosimetry in healthcare and mining applications, which can achieve 12-18 bit resolution with 0.01-1 µJ energy dissipation, and 2) an ADC-less neural signal acquisition system with direct Analog to Time Conversion at 13pJ/Sample. The second part (Chapters 3 and 4) of this dissertation will involve the fundamentals of developing secure energy-efficient electro-quasistatic (EQS) communication techniques for IoB wearables as well as implants, and will demonstrate  2 examples: 1) Adiabatic Switching for breaking the αCV^2f limit of power consumption in capacitive voltage mode human-body communication (HBC), and 2) Bi-Phasic Quasistatic Brain Communication (BP-QBC) for fully wireless data transfer from a sub-6mm^3, 2 µW brain implant. A custom modulation scheme, along with adiabatic communication enables wireline-like energy efficiencies (<5pJ/b) in HBC-based wireless systems, while the BP-QBC node, being fully electrical in nature, demonstrates sub-50pJ/b efficiencies by eliminating DC power consumption, and by avoiding the transduction losses observed in competing technologies, involving optical, ultrasound and magneto-electric modalities. Next in Chapter 5, we will show an implementation of a reconfigurable system that would include 1) a human-body communication transceiver and 2) a traditional wireless (MedRadio) transceiver on the same integrated circuit (IC), and would demonstrate methods to switch between the two modes by detecting the placement of the transmitter and receiver devices (on-body/away from the body). Finally, in Chapter 6, we shall show a technique of augmenting security in resource-constrained devices through authentication using the Analog/RF properties of the transmitter, which are usually discarded as non-idealities in a digital transceiver chain. This method does not require any additional hardware in the transmitter, making it an extremely promising technique to augment security in highly resource-constrained scenarios. Such energy-efficient intelligent sensing and secure communication techniques, when combined with intelligent in-sensor-analytics at the resource-constrained nodes, can potentially pave the way for perpetual, and even batteryless systems for next-generation IoT, IoB and healthcare applications.</p>