Digital System DesignAnalog– time varying signals that can take on any valueacross a continuous range of voltage, current orother metricDigital– signals are modeledwith two states, 0 or 1– underneath it is all analogDigital logic levelsTTL logic levels with noise marginsSending system: Receiving system:VOL: output low voltage VIL: input low voltageVOH: output high voltage VIH: input high voltageWhy digital? Reproducibility of results Outputs of analog circuits vary withtemperature, power supply voltage, componentaging Ease of design Logic vs calculus,e.g. digital vs analog computer Flexibility and functionality Programmability – tools Speed Economy … and the technology keeps improving!Digital System DesignSystem– orderly interconnection of parts into ameaningful whole– interactions and interconnections definethe systemWhat are the system components?… depends entirely on your point of viewComponents/InterfacesBoardProgrammable Logic devicesIntegrated circuitsGatesTransistorsIC Manufacturing processDevice physicsClosed Digital SystemGajski-KuhnY-ChartGajski, D., Kuhn, R.: New VLSITools – Guest Editors’Introduction. IEEE Computer,Bd. 16,1983 (original)Walker, R., Thomas, D.: A Modelfor design Representationand Synthesis. Proc. DesignAutomation Conference, 1985(refinement)Digital System DesignSimple systems can be designed by oneperson using ad hoc methodsReal-world systems are design by teams− require a systematic modular designmethodology− decompose system to define components tobe designed− define information needed and produced− define relationships between components− dependencies, sequences


Memory and Programmable Logic
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