EECS 150 Fa04 Lecture 211EECS 150 - Components and Design Techniques for Digital SystemsLec02 – CMOS Technology9-2-04David CullerElectrical Engineering and Computer SciencesUniversity of California, Berkeleyhttp://www.eecs.berkeley.edu/~cullerhttp://www-inst.eecs.berkeley.edu/~cs1502Outline• Summary of last time• Overview of Physical Implementations• CMOS devices• Announcements/Break• CMOS transistor circuits– basic logic gates– tri-state buffers– flip-flops» flip-flop timing basics» example use» circuits3We will learn in CS 150 …• Language of logic design– Logic optimization, state, timing, CAD tools• Concept of state in digital systems– Analogous to variables and program counters in software systems• Hardware system building– Datapath + control = digital systems• Hardware system design methodology– Hardware description languages: Verilog– Tools to simulate design behavior: output = function (inputs)– Logic compilers synthesize hardware blocks of our designs– Mapping onto programmable hardware (code generation)• Contrast with software design– Both map specifications to physical devices– Both must be flawless…the price we pay for using discrete math4What is logic design?• What is design?– Given problem spec, solve it with available components– While meeting criteria for size, cost, power, beauty, elegance, etc.• What is logic design?– Choose digital logic components to perform specified control, data manipulation, or communication function and their interconnection– Which logic components to choose?Many implementation technologies (fixed-function components, programmable devices, individual transistors on a chip, etc.)– Design optimized/transformed to meet design constraints5Source: Microsoft EncartasensesensedriveANDWhat is digital hardware?• Devices that sense/control wires carrying digital values (physical quantity interpreted as “0” or “1”)– Digital logic: voltage < 0.8v is “0”, > 2.0v is “1”– Pair of wires where “0”/“1” distinguished by which has higher voltage (differential)– Magnetic orientation signifies “0” or “1”• Primitive digital hardware devices– Logic computation devices (sense and drive)» two wires both “1” - make another be “1” (AND)» at least one of two wires “1” - make another be “1” (OR)» a wire “1” - then make another be “0” (NOT)– Memory devices (store)» store a value» recall a value previously stored6Overview of Physical Implementations• Integrated Circuits (ICs)– Combinational logic circuits, memory elements, analog interfaces. • Printed Circuits (PC) boards– substrate for ICs and interconnection, distribution of CLK, Vdd, and GND signals, heat dissipation. • Power Supplies– Converts line AC voltage to regulated DC low voltage levels. • Chassis (rack, card case, ...) – holds boards, power supply, provides physical interface to user or other systems. • Connectors and Cables. The stuff out of which we make systems.EECS 150 Fa04 Lecture 227Integrated Circuits• Primarily Crystalline Silicon• 1mm - 25mm on a side• 100 - 200M transistors• (25 - 50M “logic gates")• 3 - 10 conductive layers• 2002 - feature size ~ 0.13um = 0.13 x 10-6m • “CMOS” most common -complementary metal oxide semiconductor• Package provides:– spreading of chip-level signal paths to board-level – heat dissipation. • Ceramic or plastic with gold wires. Chip in Package8Printed Circuit Boards• fiberglass or ceramic• 1-20 conductive layers • 1-20in on a side • IC packages are soldered down.Multichip Modules (MCMs)• Multiple chips directly connected to a substrate. (silicon, ceramic, plastic, fiberglass) without chip packages.9Integrated Circuits• Moore’s Law has fueled innovation for the last 3 decades.• “Number of transistors on a die doubles every 18 months.”• What are the side effects of Moore’s law?10Integrated Circuits• Uses for digital IC technology today:– standard microprocessors» used in desktop PCs, and embedded applications» simple system design (mostly software development)– memory chips (DRAM, SRAM)– application specific ICs (ASICs)» custom designed to match particular application» can be optimized for low-power, low-cost, high-performance» high-design cost / relatively low manufacturing cost– field programmable logic devices (FPGAs, CPLDs)» customized to particular application after fabrication» short time to market» relatively high part cost– standardized low-density components» still manufactured for compatibility with older system designs11close switch (if A is “1” or asserted)and turn on light bulb (Z)A Zopen switch (if A is “0” or unasserted)and turn off light bulb (Z)Switches: basic element of physical implementations• Implementing a simple circuit (arrow shows action if wire changes to “1”):Z ≡ AAZ12CMOS DevicesCross 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 View• MOSFET (Metal Oxide Semiconductor Field Effect Transistor). nFETpFETEECS 150 Fa04 Lecture 2313What Complementary about CMOS?• Complementary devices work in pairsn-channelopen when voltage at G is lowcloses when:voltage(G) > voltage (S) + εp-channelclosed when voltage at G is lowopens when:voltage(G) < voltage (S) – εGS DGS D14Transistor-level Logic Circuits (inv)• Inverter (NOT gate):VddGndVddGnd0 voltsin out3 voltswhat is the relationship between in and out?15Logical Values• Threshold– Logical 1 (true) : V > Vdd –V th– Logical 0 (false) : V < Vth• Noise margin?V+30Logic 1Logic 0Vout+30Logic 0Input VoltageLogic 1Input VoltageVin+5Fin outTTFnot( out, in) 16Big idea: Self-restoring logic• CMOS logic gates are self-restoring– Even if the inputs are imperfect, switching time is fast and outputs go rail to rail– Doesn’t matter how many you cascade» Although propagation delay increases• Manage fan-out to ensure sharp and complete transition17Element of Time• Logical change is not instantaneous• Broader digital design methodology has to make it appears as such– Clocking, delay estimation, glitch avoidanceVout+30Vin+5Propagation delay18AnnouncementsIf you are on the wait list and would like to get into the class you must:• Turn in an
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