Transcript ppt

ESE370:
Circuit-Level
Modeling, Design, and Optimization
for Digital Systems
Day 21: October 20, 2014
Design Space Exploration
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Penn ESE370 Fall2014 -- DeHon
Today
• Finish Ratioed Gates (quickly)
• Example to discuss and illustrate design
space
– You will want to be exploring design space
for Project 1
– Chance to talk about trends
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Penn ESE370 Fall2014 -- DeHon
Size for R0/2 drive
• Established
– Rp0~=2R0
– To pull below 0.1Vdd
• Wn>=4Wp
• So:
– Rp=2R0/Wp=R0/2
– Solve Wp=4
– Wn>=4Wp
– Solve Wn=16
Penn ESE370 Fall2014 -- DeHon
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How size for R0/2 drive?
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Penn ESE370 Fall2014 -- DeHon
How size for R0/2 drive?
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Penn ESE370 Fall2014 -- DeHon
How size for R0/2 drive?
• How size K-input nor?
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Penn ESE370 Fall2014 -- DeHon
When better than CMOS nor-k?
• Better = smaller, lower input capacitance
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Penn ESE370 Fall2014 -- DeHon
Which Implementation is
faster in ratioed logic?
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Penn ESE370 Fall2014 -- DeHon
Preferred Gate
• Ratioed Logic (PMOS Load)
• CMOS
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Penn ESE370 Fall2014 -- DeHon
Design Problem
• Identify equivalence of two 32b inputs
• Minimize Total Energy
• Assume match case uncommon
– Most of the time, it won’t be matched
• Deliberately focus on Energy to
complement project
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Penn ESE370 Fall2014 -- DeHon
Idea: Design Space Explore
• Identify options
– All the knobs you can turn
• Explore space systematically
• Formulate continuum where possible
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Penn ESE370 Fall2014 -- DeHon
Problem Solvable
• First, make sure we have a solution
– …so we know our main goal is optimization
• What look like built out of nand2 gates?
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Penn ESE370 Fall2014 -- DeHon
Total Power
• Ptot ≈ a(½Cload+Csc)V2f+VI’s(W/L)e-Vt/(nkT/q)
• Ptot ≈ a(½Cload+Csc)V2f
+PlowV2/Rpon
+(1-Plow)VI’s(W/L)e-Vt/(nkT/q)
• What can we do to reduce power?
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Penn ESE370 Fall2014 -- DeHon
Knobs
• What are the options and knobs we can
turn?
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Penn ESE370 Fall2014 -- DeHon
Ideas
• We know many things can do to our
circuits
• Design space is large
• Systematically identify dimensions
• Identify continuum tuning when possible
• Watch tradeoffs
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Penn ESE370 Fall2014 -- DeHon
Admin
• Project
– Should have simulated baseline
– List of optimizations to try
• If don’t have list talk with Spencer or André
during office hours
– Milestone is a bare minimum
• Really should be into exploring options this
week
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Penn ESE370 Fall2014 -- DeHon