Digital System Design Lecture 1: Introduction

Digital System DesignLecture 1: IntroductionAmir Masoud Gharehbaghiamgh@mehr.sharif.edu

Table of Contents{{{{{{Introduction to Digital SystemsDigital Versus Analog SystemsContemporary Digital DesignModeling AbstractionsAbstraction LevelsY ChartSharif University of Technology2

System{{System: a set of related parts thatactuate as a whole to achieve agiven goal.System has:zzz{InputsOutputsBehaviorBehavior: a function that translatesinputs to outputs.Sharif University of Technology3

System (cont.){An entity consisting of Hardwareand SoftwarezHardware:High speed{ Low power consumption{ Less price (probably){zSoftware:Flexible{ Easy to modify and upgrade{Sharif University of Technology4

Hardware Systems{Components are Electronic blobkszzzAnalogDigitalMixed-SignalSharif University of Technology5

Analog Systems{Process time-varying signalszTake value across a continuous range{{{zVoltageCurrent Continous timeSharif University of Technology6

Digital Systems{{The same as analog systems.But they pretend they don’t!zzFunction over finite values.In discrete time domain.Sharif University of Technology7

Mixed-Signal Systems{{Have both analog and digital parts.Digital part:z{Control and data process. (DSP)Analog part:zSensing and actuating environment.Sharif University of Technology8

Advantages of Digital Systems{{{{{{{{High noise immunityAdjustable precisionEase of design (automation) andfabrication, therefore, low costBetter ReliabilityLess need to calibration and maintenanceEase of diagnosis and repairEasy to duplicate similar circuitsEasily controllable by computerSharif University of Technology9

Disadvantages of Digital Systems{{Lower speedNeeds converters to communicatewith real world, therefore moreexpensive and less precisionzzDigital to Analog (D/A)Analog to Digital (A/D)Sharif University of Technology10

Digital Abstraction{{{Digital circuits actually deal withanalog voltages and currents.Digital abstraction allows analogbehavior to be ignored (most cases)Simplest form of abstraction isBinary system, two values exists:zz0, Low, False1, High, TrueSharif University of Technology11

Digital Abstraction (cont.){{Association of arange of analogvalues with eachlogic value (0, 1).The differencebetween therange boundariesis called noisemargin.Sharif University of Technology12

Synchronous vs. Asynchronous{{{Synchronous system: Elementschange their values at certainspecified times (clock event).Asynchronous systems: Outputs canchange at any time.Example: digital alarm set to 13:59zzSynchronous: 12:59 - 13:00 - 13:01Asynchronous: 12:59 - 13:59 - 13:00Sharif University of Technology13

Gates{{{Gates are the most basic digital devices.A gate has one or more inputs andproduces an output that is a function ofthe current input values.A gate is a combinational circuit,because its output depends only on thecurrent input combination.Sharif University of Technology14

Flip-Flops{{{{{{A flip-flop is a devices that store either a 0 or a 1.The state of a flip-flop is the value currently stored.The stored value can only be changed at certaintimes, regulated by a "clock" input.A digital circuit that contains flip-flops is called asequential circuit.The output of a sequential circuit depend, at anytime, not only in its current input but also on thepast sequence of inputs that have been applied to itA sequential circuit has memory of past events.Sharif University of Technology15

Contemporary Digital Design{Major changes in recent years:zzz{More complex designs (SoC, SoPC)Shorter Time-to-Market (TTM)Cheaper productsScalezzPervasive use of computer-aideddesign tools over hand methodsMultiple levels of design representationSharif University of Technology16

Contemporary Digital Design(cont){Timezzzz{Emphasis on abstract design representationsProgrammable rather than fixed functioncomponentsAutomatic synthesis techniquesImportance of sound design methodologiesCostzzHigher levels of integrationuse of simulation to debug designsSharif University of Technology17

EDA/CAD Tools{{{CAD (Computer Aided Design) toolsare nowadays essential part ofdigital design.HDLs (Hardware DescriptionLanguage)Design Automation (DA) helps usimprove productivity and alsopredictability of behaviorSharif University of Technology18

EDA/CAD Tools (cont.){{{{{Schematic EntryHDL Compilers and SimulatorsSynthesis ToolsTiming AnalyzersVerification ToolszzzzSimulatorsTestbenchesDesign CheckersFormal and Semi-Formal VerifiersSharif University of Technology19

Integrated Circuits (ICs){{An IC is a collection of gates fabricatedon a single silicon chip.Different sizes of ICs:zzzz{SSI (Small Scale Integrated){ Small number of gates (1 to 30 gates)MSI (Medium Scale Integrated){ Decoder, counter, register (30 to 300 gates)LSI (Large Scale Integrated){ Small memories, PLDs (300 to 300k gates)VLSI (Very Large Scale Integrated){ Microprocessors, memories ( 1M transistors)P4 has more than 42M transistors!Sharif University of Technology20

SSI ICs{{{{Dual in-line pin (DIP)packages.A pin diagram shows theassignment of devicesignals to package pins.Nowadays, SSI ICs areused as "glue" to tietogether largercomponents in complexsystems.SSI ICs have beenlargely supplanted byPLDs (ProgrammableLogic Devices).Sharif University of Technology21

Programmable Logic Devices (PLDs){{{{{{Some ICs can have their logic function"programmed" into them after they aremanufactured.Most of them can even be reprogrammed, whichallows bugs to be corrected without replacing orrewiring the device.PLD (PLA or PAL): two-level structure of AND andOR gates with user-programmable connections.CPLDs (Complex PLDs) and FPGAs (FieldProgrammable Gate Arrays) were devised toaccommodate larger systems.HDLs and the respective tools allow a design tobe compiled, synthesized, and downloaded into adevice in a short time.This permits rapid prototyping to be a reality.Sharif University of Technology22

Design HierarchySystemData PathControllerData RegisterState RegisterCombinational LogicCombiational LogicSharif University of Technology23

Design ProcessAbstraction LevelsHighLowSystem SpecificationSystemFunctional ModulesGateCircuitDeviceSharif University of Technology24

Abstraction LevelsDesign LevelsDesign DescriptionsPrimitive ComponentsSystem (Architecture)System LanguagesHigh-Level LanguagesFunctional BlocksBehavioral (Algorithmic)HDLsMath EquationsFunctional BlocksFunctional (RTL)HDLsFSMsRegistersALUs, Multiplexers, LogicHDLsBoolean EquationsTiming DiagramsGate NetlistLogic GatesFlip-FlopsCircuit (Switch)Transistor NetlistTransistorsDevice (Geometrical)GraphicalPolygonsSharif University of Technology25

Abstraction Levels (simple){Architectural Levelz{Logic Levelz{Operations implemented by resourcesLogic functions implemented by gatesGeometrical LevelzDevices are geometrical objectsSharif University of Technology26

Modeling Views{Behavioral view:z{Structural view:z{Abstract functionAn interconnectionof partsPhysical view:zPhysical objectswith size andpositionsSharif University of Technology27

Modeling Views (cont.){Correspondence Physical designExtractionSharif University of Technology28

Y ChartSharif University of Technology29

Sharif University of Technology 15 Flip-Flops {A flip-flop is a devices that store either a 0 or a 1.{The state of a flip-flop is the value currently stored.{The stored value can only be changed at certain times, regulated by a "clock" input. {A digital circuit that contains flip-flops is called a sequential circuit. {The output of a sequential circuit depend, at any