Calibration

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Calibration of Setup and Hold
time for Latches and Flip-flops
Chia-Hao Chang

Prof. Puneet Gupta

Outline:
1.
2.
3.
4.
5.

Definition of setup and hold time
Measurement methodology
Library file formulation
Library characterization tools
Reference

Definition of Setup and Hold Time
Setup and Hold Times Specification for
Rising-Edge-Triggered Flip-Flop

Setup and Hold Sepcification for
High-Enable Latch

[1]
When Violating the Setup or Hold Constraint :

extra delay

Voltage Keeper

Conventional TSPC Flip-Flop Design [2]

Will cause Clock-Q delay to increase or [3]
even flip the Output

Measurement Methodology(1/3)

[4]

Approaches for setup and hold time determination: [4]
1. Minimizing T_setup +T_hold with some given delay allowance
2. Minimizing T_setup + T_clk2Q [5] -> Maximize the Perfomance
3. (Industrial approach) 5-10% degradation in the minimal possible T_clk2Q delay

Measurement Methodology(2/3)

[7]

Measurement Methodology(3/3)

Searching methodologies for critical skew for the onset of metastability
1. Binary search (Mostly applied) : mouths of runtime for enterprise libraries[5]
2. Using Newton-Raphson method to solve Differential Equations of Metastability[6]
4x ~ 10x faster

A Transmission Gate
Based Positive-edge
triggered master-slave
register

Library File Formulation
To be calibrated:
setup_rising, setup_falling,
hold_rising, or hold_falling

The table requires the 9
searching processes for
different sets of indices

pin (D) {
direction : input;
...
timing () {
related_pin : "CK";
timing_type : "setup_rising";
rise_constraint ("setuphold_template_3x3") {
index_1("0.4, 0.57, 0.84"); /* Data transition Time*/
index_2("0.4, 0.57, 0.84"); /* Clock transition Time*/
values( /* 0.4 0.57 0.84 */ \
/* 0.4 */ "0.063, 0.093, 0.112", \
/* 0.57 */ "0.526, 0.644, 0.824", \
[10]
/* 0.84 */ "0.720, 0.839, 0.930");


Setup time constraints for
output rising case

Library Characterization Tools
LibDev Specific Software (~2008)[9]
Company

Layout

Characterization

Altos Design Automation

Liberate

Cadence

SignalStorm

Optimization

Fenix Design Automation

Crossfire

Legend Design
Technology
Library Technologies
Magma Design
Automation

CharFlo-Memory
LibChar

Library Creator

Prolific

ProGenesis

Radix Tools

Synopsys

VeriPool
Z Circuit
Zenasis Technologies

CellOpt, LowSkew

SiliconSmart

Nangate

Sagantec
SIMUCAD Design
Automation

Verification

Library Creator, Library
Characterizer

Library Creator

Std. cell library
characterization.

xlicdsm
SiClone, SiFix

Library Creator, Liberty
Analyzer

SiFix, DFM-Fix
AccuCell

Cadabra

Liberty NCX

Circuit Explorer

GSpice (free)
ZChar

Liberty parser, Liberty
screener, Library
Compiler
Library Analyzer

ZenTime-CT

Reference(1/2)
[1] W. Roethig, “Library Characterization and Modeling for 130 nm and 90 nm SOC Design,”
Proceedings of the IEEE International SOC Conference, pp. 383–386, September 2003.
*2+ Wikipedia, “Flip-flop (electronics)”
http://en.wikipedia.org/wiki/Flip-flop_(electronics)
*3+ K. Yang, “Clocking Methodology and Flip-Flops,” EE215B lecture note, Winter 2010
[4] S. Sundareswaran,“Statistical Characterization For Timing Sign-Off: From Silicon to Design and
Back to Silicon,” Doctorial thesis of the University of Texas at Austin, 2009
[5] V. Stojanovic and V.G. Oklobdzija, “Comparative Analysis of Master- Slave Latches and FlipFlops for High-Performance and Low-Power Systems,” IEEE Journal of Solid-State Circuits, Vol.
34, No. 4, pp. 536–548, April 1999.
[6] Srivastava, S.; Roychowdhury, J.; , "Rapid and Accurate Latch Characterization via Direct
Newton Solution of Setup/Hold Times," Design, Automation & Test in Europe Conference &
Exhibition, 2007. DATE '07 , vol., no., pp.1-6, 16-20 April 2007
[7] Salman, E.; Dasdan, A.; Taraporevala, F.; Kucukcakar, K.; Friedman, E.G.; , "Pessimism reduction
in static timing analysis using interdependent setup and hold times,"Quality Electronic
Design, 2006. ISQED '06. 7th International Symposium on , vol., no., pp.6 pp.-164, 27-29
March 2006
[8] Srivastava, S.; Roychowdhury, J.; , "Independent and Interdependent Latch Setup/Hold Time
Characterization via Newton–Raphson Solution and Euler Curve Tracking of State-Transition
Equations," Computer-Aided Design of Integrated Circuits and Systems, IEEE Transactions on ,
vol.27, no.5, pp.817-830, May 2008

Reference(2/2)
[9] Review of Library Develop tools in the personal website of Oleg S. SEVALNEV :
http://olegsevalnev.tripod.com/
[10] J. Bhasker and Rakesh Chadha, “Static Timing Analysis for Nanometer Designs: A Practical
Approach. Springer,” first edition, April 2009.

Related Study
• Setup and Hold Time interdependence
Modeling in Static Timing Analysis [7][8]

Require more SPICE simulation

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