Τα αναλογικά φίλτρα συνεχούς χρόνου αποτελούν απαραίτητα μέρη ακόμη και στις πιο μοντέρνες ηλεκτρονικές συσκευές, οι οποίες λειτουργούν, κατά το μεγαλύτερο τμήμα τους ψηφιακά. Η εξήγηση είναι απλή, αν αναλογιστεί κανείς πρώτον, ότι, αποτελούν τις ενδιάμεσες βαθμίδες μεταξύ του φυσικού κόσμου και τις –κατά τα άλλα ψηφιακές– συσκευές και δεύτερον ότι, μπορούν να λειτουργήσουν σε υψηλές συχνότητες, όπου τα ψηφιακά κυκλώματα δεν μπορούν. Η προσπάθεια για όλο και πιο βελτιωμένα κυκλώματα, κάνει τους σχεδιαστές ηλεκτρονικών κυκλωμάτων να ψάχνουν για νέες μεθόδους σχεδίασης. Μία από αυτές είναι η σχεδίαση με χρήση τεχνικών τρόπου ρεύματος (current mode), χρήση της οποίας γίνεται στην παρούσα διδακτορική διατριβή. Είναι γνωστό ότι, έως και πριν από μερικά χρόνια, η σχεδίαση κυκλωμάτων γινόταν, σχεδόν αποκλειστικά, για λειτουργία σε τρόπο τάσης. Αυτό σημαίνει ότι, για τα κυκλώματα αυτά, οι ηλεκτρικές μεταβλητές εισόδου και εξόδου είναι τάσεις αφού, η είσοδος των χρησιμοποιούμενων ηλεκτρονικών βαθμίδων είναι υψηλής εμπέδησης ενώ η έξοδός τους χαμηλής. Τα κυκλώματα τρόπου τάσης σχεδιάζονται, ώστε, να λειτουργούν σε αυτές τις στάθμες εμπέδησης, παρά το γεγονός ότι, τα στοιχειώδη ηλεκτρονικά στοιχεία, τα τρανζίστορ, συμπεριφέρονται ως ελεγχόμενες πηγές ρεύματος. Αυτό ακριβώς το γεγονός εκμεταλλεύονται τα κυκλώματα τρόπου ρεύματος, τα οποία, λόγω του ότι εμφανίζουν χαμηλή εμπέδηση εισόδου και υψηλή εμπέδηση εξόδου, επεξεργάζονται ρεύματα απλοποιώντας ταυτόχρονα τον τρόπο σχεδίασης. Για να είναι πραγματικά εφικτή η σχεδίαση για τα κυκλώματα τρόπου ρεύματος είναι απαραίτητο ένα τουλάχιστον ενεργό δομικό στοιχείο. Στην παρούσα διατριβή ως δομικό στοιχείο μελετάται, καταρχήν, ο απλός ενισχυτής ρεύματος. Ο ενισχυτής αυτός αποτελεί τη βάση του διαφορικού ενισχυτή ρεύματος, που με τη σειρά του αποτελεί ένα νέο δομικό στοιχείο πολύ πιο ευέλικτο για ανάπτυξη νέων κυκλωμάτων αναλογικής επεξεργασίας σήματος. Προκύπτει ότι, ο διαφορικός ενισχυτής ρεύματος, ο οποίος λειτουργεί συνήθως, έχοντας ενίσχυση ρεύματος ίση ή λίγο μεγαλύτερη από τη μονάδα, μπορεί να δώσει κυκλώματα, που λειτουργούν σε υψηλότερες συχνότητες συγκριτικά με τα κυκλώματα τρόπου τάσης. Αρκετά κυκλώματα μπορούν να σχεδιαστούν με βάση, είτε τον απλό, είτε το διαφορικό ενισχυτή ρεύματος. Με τη βοήθειά των δύο αυτών στοιχείων αναπτύσσεται ένα πλήθος από βασικά κυκλώματα αναλογικής επεξεργασίας σήματος, όπως εξομοιωμένοι επαγωγοί, ολοκληρωτές, ταλαντωτές καθώς και ενεργά φίλτρα. Στη διατριβή αυτή, αναπτύσσεται, καταρχήν, η σχεδίαση διαφόρων βασικών αναλογικών δομικών βαθμίδων και ακολούθως, παρουσιάζονται οι τεχνικές για τη σχεδίαση ενεργών φίλτρων, ακολουθώντας δύο βασικές μεθόδους, όπως η μέθοδος διασύνδεσης βαθμίδων δεύτερης τάξης και η μέθοδος συναρτησιακής και τοπολογικής εξομοίωσης LC παθητικών κυκλωμάτων. Η μέθοδος της τοπολογικής εξομοίωσης κυκλωμάτων είναι αρκετά ελκυστική, λόγω των δυνατοτήτων, που προσφέρει. Είναι αρκετά εύκολη κατά το σχεδιασμό, τόσο τον ηλεκτρονικό όσο και τον φυσικό (layout), καθώς χρησιμοποιεί επαναλαμβανόμενες δομές. Δύο από τις τεχνικές, που ανήκουν στην κατηγορία της τοπολογικής εξομοίωσης κυκλωμάτων και αναπτύσσονται εδώ, είναι η σχεδίαση κυκλωμάτων με τεχνική τύπου "leapfrog" και η κυματική τεχνική. Με βάση τον διαφορικό ενισχυτή ρεύματος αναπτύσσεται ο τελεστικός ενισχυτής ρεύματος. Το στοιχείο αυτό είναι χρήσιμο σε εφαρμογές, όπου απαιτείται υψηλή ενίσχυση ρεύματος. Η ενίσχυση μπορεί να είναι μεταβαλλόμενη και εξαρτώμενη από μία τάση πόλωσης και αυτό κάνει τον τελεστικό ενισχυτή ρεύματος ένα αρκετά χρήσιμο στοιχείο στην ανάπτυξη εφαρμογών. Η ανάπτυξη ενός τελεστικού ενισχυτή ρεύματος παρουσιάζεται στο τέλος της διατριβής. Όλα τα κυκλώματα, που προτείνονται στην παρούσα διατριβή, είναι ολοκληρώσιμα σε οποιαδήποτε κοινή τεχνολογία ολοκλήρωσης. Ωστόσο, τα προτεινόμενα κυκλώματα σχεδιάζονται για CMOS τεχνολογία, επειδή είναι εξαιρετικά διαδεδομένη και κατάλληλη για τις περισσότερες εφαρμογές αναλογικής επεξεργασίας σήματος. Επιπλέον, τα CMOS κυκλώματα μπορούν σχετικά εύκολα να μετατραπούν σε διπολική ή και BiCMOS τεχνολογία, αφού τοπολογικά διατηρούν την ίδια περίπου δομή. / Continuous-time analog filters are essential parts even of the most modern electronic systems, which in their main part operate digitally. We can explain this by thinking, first, that analog circuits are usually used as necessary intermediate stages between the natural world signals and the electronic digital systems and second, that they are more suitable for operation at high frequencies compared to digital circuits. The designers of electronic circuits in their effort to improve circuits investigate for new design methods. Such a recent method is the so called "current-mode method". Current-mode circuits suitable, mainly for filtering applications, are studied in this thesis. It is known that until recently electronic circuits were considered as circuits operating in voltage-mode. This means that the electric variables for these circuits were taken mainly as voltages in spite of the fact that the elementary electronic devices, that is the transistors, behave as controlled current sources. On the contrary, current-mode circuits take advantage of the real nature of the transistors and thus process currents instead of voltages. This way, the circuit design procedure is significantly simplified, the derived current-mode circuits are much simpler in their structure and in addition, they show better performance at high frequencies. A structural active element is always necessary in every active filter either in the voltage or in the current-mode domain. In this thesis, a single input current amplifier is studied, as such structural active element. This amplifier is used as a subcircuit for obtaining the differential current amplifier, which, accordingly, is used as a new basic active device for the development of new analog signal processing circuits. It is found that the differential current amplifier, which usually operates having low current gain, is suitable for operation at high frequencies comparable to the fT of the transistors used in the amplifier. It is shown that various circuits of general purpose can be obtained, based on a single or a differential current amplifier. In addition, a number of new analog circuits suitable for signal processing are proposed in this thesis. Among them, there are lossy and lossless integrators, simulated inductors, and oscillators. However, emphasis is given to the development of integrated active filters of high order by following various design methods. As a result, the method of the topological simulation of passive LC filter prototypes appears to be more attractive for obtaining high order filters, due to the many possibilities that this method offers. All the proposed circuits in this thesis are suitable for integration in CMOS technology, which is more suitable for analog signal processing applications. Simulation and experimental results taken from implemented integrated circuits verify the accuracy of operation of the proposed circuits and their suitability for practical applications.

The development of modern integration technologies is normally driven by the needs of digital CMOS circuit design. Rapid progress in silicon VLSI technologies has made it possible to implement multi-function and high performance electronic circuits on a single die. Coupled with this, the need for interfacing digital blocks to the external world resulted in the integration of analog blocks such as A/D and D/A converters, filters and oscillators with the digital logic on the same die. Thus, mixed signal system-on-chip (SOC) solutions are becoming a common practice in the present day integrated circuit (IC) technologies. In digital domain, aggressive technology scaling redefines, in many ways, the role of interconnects vis-`a-vis the logic in determining the overall performance. Apart from signal integrity, power dissipation and reliability issues, delays over long interconnects far exceeding the logic delay becomes a bottleneck in high speed operation. Moreover, with an increasing density of chips, the number of interchip connections is greatly increased as more and more functions are put on the same chip; thus, the size and performance of the chip are mostly dominated by wiring rather than devices. One of the most promising approaches to solve the above interconnection problems is the use of multiple-valued logic (MVL) inside the chip [Han93, Smi88]. The number of interconnections can be directly reduced with multiple valued signal representation. The reduced complexity of interconnections makes the chip area and delay much smaller leading to reduced cross talk noise and improved reliability. Thus, the inclusion of multiple-valued logic in a otherwise mixed design, consisting of analog and binary logic, can make the transition from analog to digital world much more smoother and at the same time improve the overall system performance. As the sizes of integrated devices decrease, maximum voltage ratings also rapidly decrease. Although decreased supply voltages do not restrict the design of digital circuits, it is harder to design high performance analog and multiple valued integrated circuits using new processes. As an alternative to voltage-mode signal processing, current-mode circuit techniques, which use current as a signal carrier, are drawing strong attention today due to their potential application in the design of high-speed mixed-signal processing circuits in low-voltage standard VLSI CMOS technologies. Industrial interest in this field has been propelled by the proposal of innovative ideas for filters, data converters and IC prototypes in the high frequency range [Tou90, Kol00]. Further, in MVL design using conventional CMOS processing, different current levels can be easily used to represent different logic values. Thus the case for an integrated approach to the design of analog, multi-valued and binary logic circuits using current-mode techniques seems to be worth considering. The work presented in this thesis is an effort to reaffirm the utility of current-mode circuit techniques to some of the existing as well as to some new areas of circuit design. We present new algorithms for the synthesis of a class of analog and multiple-valued logic circuits assuming an underlying CMOS current-mode building blocks. Next we present quaternary current-mode signaling scheme employing a simple encoder and decoder architecture for improving the signal delay characteristics of long interconnects in digital logic blocks. As an interface between analog and digital domain, we present an architecture of current-mode flash A/D converter. Finally, low power being a dominant design constraint in today IC technology, we present a scheme for static power minimization in a class of Current-mode circuits.

Sensor interfaces are needed to communicate the measured real-world analog values to the base¬band digital processor. They are dominated by the presence of high accuracy, high resolution analog to digital converters (ADC) in the backend. On most occasions, sensing is limited to small range measurements and low-modulation sensors where the complete dynamic range of ADC is not utilized. Designing a subsystem that integrates the sensor and the interface circuit and that works with a low resolution ADC requiring a small die-area is a challenge. In this work, we present a CMOS based area efficient, integrated sensor interface for applications like capacitance, temperature and dielectric-constant measurement. In addition, potential applica-tions for this work are in Cognitive Radios, Software Defined Radios, Capacitance Sensors, and location monitoring. The key contributions in the thesis are: 1 High Sensitivity Frequency-domain CMOS Capacitance Interface: A frequency domain capacitance interface system is proposed for a femto-farad capacitance measurement. In this technique, a ring oscillator circuit is used to generate a change in time period, due to a change in the sensor capacitance. The time-period difference of two such oscillators is compared and is read-out using a phase frequency detector and a charge pump. The output voltage of the system, is proportional to the change in the input sensor capacitance. It exhibits a maximum sensitivity of 8.1 mV/fF across a 300 fF capacitance range. 2 Sensitivity Enhancement for capacitance sensor: The sensitivity of an oscillator-based differential capacitance sensor has been improved by proposing a novel frequency domain capacitance-to-voltage (FDC) measurement technique. The capacitance sensor interface system is fabricated in a 130-nm CMOS technology with an active area of 0.17mm2 . It exhibits a maximum sensitivity of 244.8 mV/fF and a measurement resolution of 13 aF in a 10-100 fF measurement range, with a 10 pF nominal sensor capacitance and an 8-bit ADC. 3 Frequency to Digital Converter for Time/Distance measurement: A new architecture for a Vernier-based frequency-to-digital converter (VFDC) for location monitoring is pre¬sented, in which, a time interval measurement is performed with a frequency domain approach. Location monitoring is a common problem for many mobile robotic applica¬tions covering various domains, such as industrial automation, manipulation in difficult areas, rescue operations, environment exploration and monitoring, smart environments and buildings, robotic home appliances, space exploration and probing. The proposed architecture employs a new injection-locked ring oscillator (ILR) as the clock source. The proposed ILR oscillator does not need complex calibration procedures, usually required by Phase Locked Loop (PLL) based oscillators in Vernier-based time-to-digital convert¬ers. It consumes 14.4 µW and 1.15 mW from 0.4 V and 1.2 V supplies, respectively. The proposed VFDC thus achieves a large detectable range, fine time resolution, small die size and low power consumption simultaneously. The measured time-difference error is less than 50 ps at 1.2 V, enabling a resolution of 3 mm/kHz frequency shift. 4 A bio-sensor array for dielectric constant measurement: A CMOS on-chip sensor is presented to measure the dielectric constant of organic chemicals. The dielectric constant of these chemicals is measured using the oscillation frequency shift of a current controlled os¬cillator (CCO) upon the change of the sensor capacitance when exposed to the liquid. The CCO is embedded in an open-loop frequency synthesizer to convert the frequency change into voltage, which can be digitized using an off-chip analog-to-digital converter. The dielectric constant is then estimated using a detection procedure including the calibration of the sensor. 5 Integrated Temperature Sensor for thermal management: An integrated analog temper¬ature sensor which operates with simple, low-cost one-point calibration is proposed. A frequency domain technique to measure the on-chip silicon surface temperature, was used to measure the effects of temperature on the stability of a frequency synthesizer. The temperature to voltage conversion is achieved in two steps i.e. temperature to frequency, followed by frequency to voltage conversion. The output voltage can be used to com¬pensate the temperature dependent errors in the high frequency circuits, thereby reduc¬ing the performance degradation due to thermal gradient. Furthermore, a temperature measurement-based on-chip self test technique to measure the 3 dB bandwidth and the central frequency of common radio frequency circuits, was developed. This technique shows promise in performing online monitoring and temperature compensation of RF circuits.