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- Afghahi, Morteza, 1950-
(author)
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Clocking of high speed CMOS VLSI systems
- 1991
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Doctoral thesis (other academic/artistic)abstract
- Two consequences of high level circuit integration may be increasing cost of design and cost of interconnections. Interconnection is expensive in terms of silicon area, speed and power. As far as timing is concerned. schemes of future VLSI systems may not be a simple extension of those used in the existing LSI circuits. This is because the relative importance of clock skew increases as the MOS technology develops and interconnections become slower and slower. Clock skew makes the design of VLSI synchronous circuits ineffective, complicated and failure prone. For a synchronous scheme to be useful in the VLSI environment and enjoy the experiences gained by designers, it must develop to a fast, simple, structured and robust scheme.To alleviate the adverse effects of clock skew, technological as well as circuit techniques may be employed. We have proposed a technological solution. It is suggested that a special interconnection metal layer should be introduced into the VLSI process and used for long interconnections. It is shown that by using this technique, the interconnection delay will not be a limiting factor for the performance of synchronous systems.We have also considered circuit solutions. To this end, physical causes of clock skew are investigated. It is shown that even for optimized interconnections, traditional modes of clocking results in unacceptable time performance for high speed synchronous systems. Then a new mode of clocking is presented and analysed in detail. By using this mode of clocking, the performance of synchronous systems scales with scaling the minimum feature size of MOS transistors.We have developed a synchronous scheme that is structured, simple and general. These factors also make the CMOS systems well suited for design compilation. A circuit technique is proposed that makes the design of synchronous schemes robust. Performance of different asynchronous schemes in VLSI environment is also investigated. It is shown that synchronous schemes outperforms standard asynchronous schemes for a wide range of important applications.Finally, in order to test some of the developed rules and principles, a chip has been designed as an example. In this design, a new hardware algorithm is presented for sorting. This algorithm is based on bit-serial data processing. It is shown that this design can operate at a clock frequency determined by the computational module delays and not by the clock skew.
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- Afoke, Anthony Okoro
(author)
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Some epidemiological aspects of insulin-dependent diabetes mellitus in Nigeria and Sweden
- 1993
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Doctoral thesis (other academic/artistic)abstract
- In the western world diabetes mellitus is one of the most common severe diseases in childhood, but it is rarely seen in black African populations. However, there are very few epidemiological studies of childhood diabetes in Africa and almost nothing is known of the Nigerian population. One aim of this study was therefore to estimate the prevalence of insulin dependent diabetes (IDDM) in children and adolescents and to characterize their type of diabetes.A screening of almost 78,000 school children was performed and beside some already known diabetic patients several new cases were diagnosed. It was found that IDDM is much less common than in Europe but on the other hand more common than in several Asian countries. In addition the prevalence found may be underestimated because of cultural and social factors, health care problems and high mortality in diabetes. Although most patients had a clinical picture of Malnutrition Related Diabetes (MRD) we found in some cases autoantibodies towards islet cells and insulin and furthermore the same HLA-DQ-type-associations as seen to Type 1 diabetes in caucasian diabetics.While we saw no seasonal variation of diagnosis of Nigerian IDDM, there is a pronounced such seasonal variation in Sweden. This study has tried to elucidate whether this seasonal variation is related to any differences in manifestation and clinical course. Patients diagnosed during incidence peaks had more often short duration of symptoms before diagnosis,ketonuria at diagnosis, rapid loss of endogenous insulin secretion but increase of insulin antibodies and of glycosylated haemoglobin. They had also more often infections before diagnosis and high serum immunoglobulins (IgG and IgM) up to 9 months after diagnosis. HLA-DR4 was more common in these patients. The results suggest that IDDM in Swedish children is heterogenous.
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