Digital Design and System ImplementationOverview of Physical ImplementationsIntegrated CircuitsPrinted Circuit BoardsSlide 5Slide 6CMOS DevicesLogic and Layout: NAND GateTransmission GatePass-Transistor Multiplexer4-to-1 Pass-transistor MuxAlternative 4-to-1 MultiplexerExample: Tally CircuitSlide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Example: Crossbar SwitchBarrel ShifterExample: Barrel ShifterSlide 29Slide 30Tri-state Based MultiplexerD-type Edge-triggered Flip-flopSlide 35State Machines in CMOSDigital Design and Implementation SummaryCS 150 – Spring 2007 - Lec #26 – Digital Design – 1Digital Design and System ImplementationOverview of Physical ImplementationsCMOS devicesCMOS transistor circuit functional behaviorBasic logic gatesTransmission gatesTri-state buffersFlip-flops vs. latches revisitedCS 150 – Spring 2007 - Lec #26 – Digital Design – 2The stuff out of which we make systemsOverview of Physical ImplementationsIntegrated Circuits (ICs)Combinational logic circuits, memory elements, analog interfacesPrinted Circuits (PC) boardssubstrate for ICs and interconnection, distribution of CLK, Vdd, and GND signals, heat dissipationPower SuppliesConverts line AC voltage to regulated DC low voltage levelsChassis (rack, card case, ...) 1-25 conductive layers holds boards, power supply, fans, provides physical interface to user or other systemsConnectors and CablesCS 150 – Spring 2007 - Lec #26 – Digital Design – 3Integrated CircuitsPrimarily Crystalline Silicon1mm - 25mm on a side200 - 400M effective transistors(50 - 75M “logic gates")3 - 10 conductive layers2007 feature size ~ 65nm = 0.065 x 10-6 m45nm coming on line “CMOS” most common - complementary metal oxide semiconductorPackage provides:Spreading of chip-level signal paths to board-level Heat dissipation. Ceramic or plastic with gold wiresChip in PackageCS 150 – Spring 2007 - Lec #26 – Digital Design – 4Multichip Modules (MCMs)Multiple chips directly connected to a substrate (silicon, ceramic, plastic, fiberglass) without chip packagesPrinted Circuit BoardsFiberglass or ceramic1-20in on a side IC packages are soldered downCS 150 – Spring 2007 - Lec #26 – Digital Design – 5Integrated CircuitsMoore’s Law has fueled innovation for the last 3 decades“Number of transistors on a die doubles every 18 months.”What are the consequences of Moore’s law?CS 150 – Spring 2007 - Lec #26 – Digital Design – 6Integrated CircuitsUses for Digital IC technology today:Standard microprocessorsUsed in desktop PCs, and embedded applications (ex: automotive)Simple system design (mostly software development)Memory chips (DRAM, SRAM)Application specific ICs (ASICs)custom designed to match particular applicationcan be optimized for low-power, low-cost, high-performancehigh-design cost / relatively low manufacturing costField programmable logic devices (FPGAs, CPLDs)customized to particular application after fabricationshort time to marketrelatively high part costStandardized low-density componentsstill manufactured for compatibility with older system designsCS 150 – Spring 2007 - Lec #26 – Digital Design – 7Cross SectionThe gate acts like a capacitor. A high voltage on the gate attracts charge into the channel. If a voltage exists between the source and drain a current will flow. In its simplest approximation, the device acts like a switch. Top ViewMOSFET (Metal Oxide Semiconductor Field Effect Transistor) nFETpFETCMOS DevicesCS 150 – Spring 2007 - Lec #26 – Digital Design – 11Logic and Layout: NAND GateCS 150 – Spring 2007 - Lec #26 – Digital Design – 12Transmission gates are the way to build “switches” in CMOSIn general, both transistor types are needed:nFET to pass zerospFET to pass onesThe transmission gate is bi-directional (unlike logic gates)Does not directly connect to Vdd and GND, but can be combined with logic gates or buffers to simplify many logic structuresTransmission GateCS 150 – Spring 2007 - Lec #26 – Digital Design – 13Pass-Transistor Multiplexer2-to-1 multiplexer:c = sa + s’bSwitches simplify the implementation:ss’bacCS 150 – Spring 2007 - Lec #26 – Digital Design – 144-to-1 Pass-transistor MuxThe series connection of pass-transistors in each branch effectively forms the AND of s1 and s0 (or their complement)20 transistorsCS 150 – Spring 2007 - Lec #26 – Digital Design – 15Alternative 4-to-1 MultiplexerThis version has less delay from in to outCare must be taken to avoid turning on multiple paths simultaneously (shorting together the inputs)36 TransistorsCS 150 – Spring 2007 - Lec #26 – Digital Design – 16Example: Tally CircuitN inputs: How many of these are asserted?TallyInI1NTwoOneZero……E.g., 1 input, 2 outputs: One, ZeroE.g., 2 inputs, 3 outputs: Two, One, ZeroN inputs, N+1 outputs: N, …, One, ZeroCS 150 – Spring 2007 - Lec #26 – Digital Design – 17Example: Tally Circuit01CS 150 – Spring 2007 - Lec #26 – Digital Design – 18Example: Tally CircuitCS 150 – Spring 2007 - Lec #26 – Digital Design – 19Example: Tally CircuitCS 150 – Spring 2007 - Lec #26 – Digital Design – 20Example: Tally Circuit2 inputs, 3 outputs:Two, One, ZeroI10110CS 150 – Spring 2007 - Lec #26 – Digital Design – 21Example: Tally Circuit2 inputs, 3 outputs:Two, One, ZeroI1010CS 150 – Spring 2007 - Lec #26 – Digital Design – 22Example: Tally Circuit2 inputs, 3 outputs:Two, One, ZeroCS 150 – Spring 2007 - Lec #26 – Digital Design – 23Example: Tally Circuit2 inputs, 3 outputs:Two, One, ZeroCS 150 – Spring 2007 - Lec #26 – Digital Design – 24Example: Tally Circuit2 inputs, 3 outputs:Two, One, ZeroCS 150 – Spring 2007 - Lec #26 – Digital Design – 25Example: Tally Circuit2 inputs, 3 outputs:Two, One, ZeroCS 150 – Spring 2007 - Lec #26 – Digital Design – 26Example: Crossbar SwitchN inputs, N outputs, N x N control signalsCrossBarBusiOutiNote: circuit like thisused inside Xilinxswitching matrixCS 150 – Spring 2007 - Lec #26 – Digital Design – 27Barrel ShifterBarrelShifterBusOutShiftBus ShiftCS 150 – Spring 2007 - Lec #26 – Digital Design – 28Example: Barrel ShifterN inputs, N outputs, N control signalsShift 0CS 150 – Spring 2007 - Lec #26 –
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