Design and modelling of variability tolerant on-chip communication structures for future high performance system on chip designs

The incessant technology scaling has enabled the integration of functionally complex System-on-Chip (SoC) designs with a large number of heterogeneous systems on a single chip. The processing elements on these chips are integrated through on-chip communication structures which provide the infrastructure necessary for the exchange of data and control signals, while meeting the strenuous physical and design constraints. The use of vast amounts of on chip communications will be central to future designs where variability is an inherent characteristic. For this reason, in this thesis we investigate the performance and variability tolerance of typical on-chip communication structures. Understanding of the relationship between variability and communication is paramount for the designers; i.e. to devise new methods and techniques for designing performance and power efficient communication circuits in the forefront of challenges presented by deep sub-micron (DSM) technologies. The initial part of this work investigates the impact of device variability due to Random Dopant Fluctuations (RDF) on the timing characteristics of basic communication elements. The characterization data so obtained can be used to estimate the performance and failure probability of simple links through the methodology proposed in this work. For the Statistical Static Timing Analysis (SSTA) of larger circuits, a method for accurate estimation of the probability density functions of different circuit parameters is proposed. Moreover, its significance on pipelined circuits is highlighted. Power and area are one of the most important design metrics for any integrated circuit (IC) design. This thesis emphasises the consideration of communication reliability while optimizing for power and area. A methodology has been proposed for the simultaneous optimization of performance, area, power and delay variability for a repeater inserted interconnect. Similarly for multi-bit parallel links, bandwidth driven optimizations have also been performed. Power and area efficient semi-serial links, less vulnerable to delay variations than the corresponding fully parallel links are introduced. Furthermore, due to technology scaling, the coupling noise between the link lines has become an important issue. With ever decreasing supply voltages, and the corresponding reduction in noise margins, severe challenges are introduced for performing timing verification in the presence of variability. For this reason an accurate model for crosstalk noise in an interconnection as a function of time and skew is introduced in this work. This model can be used for the identification of skew condition that gives maximum delay noise, and also for efficient design verification

Delay line based passive radio frequency identification tags

This work describes the concept, design, fabrication, and characterization of delay-based radio frequency identification (RFID) tags and RFID-based sensor tags, representing a novel RFID technology. The presented delay-based RFID concept is based on the LC-delay-line and transmission-delay-line based approaches. The proposed concept allows the realization of RFIDs and RFID-based sensor tags at any allowed radio frequency, with the limitation of realizing delay elements capable of producing required delays. The RFID configurations presented in this work are for operation at 915 MHz. Simulations are used to design and optimize components and devices that constitute the tags, and to integrate them to realize tags of different configuration. A set of fabrication processes has been developed for the realization of the tag. Characterization and field testing of these tags show that delay-based RFID approach can be used to make passive tags at ultra high frequency (UHF) and other allowed frequencies. Delay-based tags have the advantages of time domain operation, and the feasibility of complying with FCC regulations. However, size, need of isolators and circulator, and design constraints in producing higher number of bits are some of the concerns that need to be further addressed. In summary, this dissertation work presents a viable alternative RFID approach based on the delay line concept. The results obtained show great promise for further development and optimization of this approach for a wide range of commercial applications

Mathematical and fuzzy modelling of high-speed interconnections in integrated circuits.

Microstrip line are the most popular interconnection type mainly due to its planar geometry. The mode of propagation is almost a transverse electromagnetic mode of wave propagation (TEM) and can be described by the Telegrapher's equations. These facts make mathematical and fuzzy modelling of microstrip lines possible.Two types of nonuniformly coupled microstrip lines, namely, nonuniformly spaced and strictly nonuniform, are presented in this study. A new model of capacitance matrix was developed for nonuniformly spaced coupled microstrip lines. The model obtained was then translated into a Mathematica program in order to be utilised in real systems. Furthermore, a new matrix; mutual capacitance ratio matrix, was deduced from the previous model. A few valuable properties were then established from this matrix. Novel concepts were introduced to approximate capacitance of strictly nonuniform coupled microstrip lines and Mathematica programs were coded to implement these methods. The study then continued with the development of new algorithms to calculate the time delay and characteristic impedance using capacitance matrices of both types of nonuniform lines. These algorithms finally became a generalised algorithm which could be used in any type of coupled microstrip lines, uniform and nonuniform. The time delay and characteristic impedance were later used as parameters to simulate crosstalk using SPICE. Analysis of geometrical and electrical parameters of microstrip lines was performed mathematically and simulations modelled using the Mathematica package. Experimental work was also carried out to investigate the characteristic of crosstalk. All information obtained from these analyses were then fed into the developed novel fuzzy model. The model was designed to minimise crosstalk and to optimise the geometrical and electrical parameters of coupled microstrip lines simultaneously. These models have the potential to become 'multi purpose on board designing tools' for a designer before the system is finally fabricated

Pulsed laser processing of dielectric materials

The thesis investigates the wavelength dependent laser ablation in dielectric materials used for the fabrication of high density Printed Circuit Boards (PCBs) in the electronics industry. Here the market for consumer and industrial products of ever-rising complexity has led to a demand for increased miniaturisation and low costs of multi- level printed circuit boards (PCBs) interconnected by microvias, which electrically connect the various circuit layers. Laser machining offers a potential solution to this need. The main objective of the research is to investigate the wavelength-dependence of the laser machining/drilling efficiency of two important sets of PCB materials, categorised as Organics and Ceramics using a carbon dioxide laser which can be tuned across its emission spectrum in the 9pm -II pin spectral region.. The organics include commercially available electronic materials with trade names such as Kapton, Arlon, FR4 and RCC and the ceramics materials studied are alumina and low temperature co- fired ceramic (LTCC). The aim is to determine the optimum laser wavelength for maximum processing efficiency i. e. to find the wavelength where the laser parameters are best matched to the optical, thermal and mechanical properties of each of the materials. A C02 laser machining system was constructed which incorporated a novel laser source developed in the research programmes. The laser source was a MOPA system with a line-tuneable cw oscillator and a five pass power planar waveguide rf discharge-excited power operating in the so-called enhanced power regime to produce maximum peak power. An Acousto-optic modulator between the master oscillator and the amplifier allowed convenient control of pulse amplitude and duration. The system enabled the wavelength dependent studies on the wavelength and pulse energy dependence of the laser ablation properties (e. g. ablation threshold fluence and ablation rates) - to derive the so-called 'ablation spectrum' of the selected materials A comparison is made of the wavelength dependence of ablation with the room temperature absorption spectrum measured for each material using ellipsometry. It was observed that the 'ablation spectrum' information does not always appear to match the simple expectations derived from the room temperature 'absorption spectrum' of the material. This disparity in results is likely due to the change of absorption properties of material because of rise in temperature, chemical decomposition or melting of material during ablation. However, the room temperature absorption spectrum (while not adequate alone), did provide a useful guide to the selection of a sub-set of the 40+ lines that would otherwise have to be studied. The results may be of direct application in the electronics industry to increase the efficiency of laser machinin

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