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  • Static Timing Analysis

    Gra

    ph

    ics:

    A

    lexa

    nd

    ra N

    olt

    e,

    Ge

    sin

    e M

    arw

    ed

    el,

    20

    03

  • SynchronousSynchronousSynchronousSynchronous Timing Timing Timing Timing ---- ReviewReviewReviewReview

  • CombinationalCombinationalCombinationalCombinational Timing Timing Timing Timing ParametersParametersParametersParameters

    A

    B

    Z

    Propagation delay: Different timing arcs that depends on the input pattern and input port (A or B)

  • FlipFlipFlipFlip----Flop Timing Flop Timing Flop Timing Flop Timing ParametersParametersParametersParameters

    Delays can be different for rising and falling data transitions

  • Timing Timing Timing Timing ConstraintConstraintConstraintConstraint ReviewReviewReviewReview (No (No (No (No SkewSkewSkewSkew))))

  • Clock NonClock NonClock NonClock Non----IdealitiesIdealitiesIdealitiesIdealities

    Clock skew

    Spatial variation in temporally equivalent clock edges; deterministic + random, T

    sk

    Clock jitter

    Temporal variations in consecutive edges of the clock signal; modulation + random noise

    Cycle-to-cycle (short-term) tJS

    Long term tJL

    Variation of the pulse width

    Important for level sensitive clocking

  • Clock UncertaintiesClock UncertaintiesClock UncertaintiesClock Uncertainties

    Sources of clock uncertainty

  • Clock Clock Clock Clock Skew and JitterSkew and JitterSkew and JitterSkew and Jitter

    Both skew and jitter affect the effective cycle time

    Only skew affects the race margin (usually)

  • SynchonousSynchonousSynchonousSynchonous Timing Timing Timing Timing ---- SkewSkewSkewSkew

  • Clock Clock Clock Clock SkewSkewSkewSkew

  • Positive Positive Positive Positive skewskewskewskew

    Launching edge arrives before the capture edge

  • Negative Negative Negative Negative skewskewskewskew

    Capture edge arrives before the launching edge

  • Positive and Negative Positive and Negative Positive and Negative Positive and Negative SkewSkewSkewSkew

  • Impact of Clock Skew on Timing:Impact of Clock Skew on Timing:Impact of Clock Skew on Timing:Impact of Clock Skew on Timing:

    Cycle Time (Long Cycle Time (Long Cycle Time (Long Cycle Time (Long Path Path Path Path Setup CheckSetup CheckSetup CheckSetup Check))))

  • Impact of Clock Skew on Timing:Impact of Clock Skew on Timing:Impact of Clock Skew on Timing:Impact of Clock Skew on Timing:

    Race Margin (Short Path Race Margin (Short Path Race Margin (Short Path Race Margin (Short Path Hold CheckHold CheckHold CheckHold Check))))

  • Impact of Skew on Timing

    Positive skew improves performance

    Negative skew improves race margin

  • Positive and negatice Clock Skew Example

  • Clock Insertion delay

    Setup Check

    Tid-capture-Tid-launch-Tck+Tperiod-Td > Tsu

    Hold Check

    Tid-launch-Tid-capture+Tck+Td > Th

    Tperiod = Target clock period

    Tck = Popagation delay of launching flip-flop

    Td = Propagation delay of combinational cells

    Tsu = Setup time of capture flip-flop

    Tid-launch = Clock insertion delay of launch path

    Tid-capture = Clock insertion delay of capture path

    Setup Slack

    SS = Tid-capture-Tid-launch-Tck+Tperiod-Td - Tsu

    Hold Slack

    HS = Tid-launch-Tid-capture+Tck+Td - Th

    Tck

    Tid-launch

    Tid-capture

    Td

    Tsu