static timing analysis -...
TRANSCRIPT
Static Timing Analysis
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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