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Day 22: October 31, 2012 Pass Transistor Logic
ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems Day 22: October 31, 2012 Pass Transistor Logic Penn ESE370 Fall DeHon
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Teaser What does this do? Penn ESE370 Fall DeHon
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Previously Penn ESE370 Fall DeHon
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Elmore Delay For each resistor Ri in path
Compute CRi = sum of all C’s downstream of Ri Delay through Ri is Ri×CRi Penn ESE370 Fall DeHon
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Impact of Capacitance Penn ESE370 Fall DeHon
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Contact/Diffusion Capacitance
Cj – diffusion depletion Cjsw – sidewall capacitance LS – length of diffusion LS Penn ESE370 Fall DeHon
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Today Pass Transistor Circuits Elmore Delay with Cdiff>0 for CMOS
Payoff: compare pass transistor to CMOS Other benefit: exercise Elmore delay calc. Penn ESE370 Fall DeHon
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Pass Transistor Penn ESE370 Fall DeHon
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Identify Function What function? Penn ESE370 Fall DeHon
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Area Compare with CMOS circuit? Penn ESE370 Fall DeHon
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Output What does output look like (DC transfer)?
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Pass TR transfer (B=1) Penn ESE370 Fall DeHon
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CMOS Inverter Transfer
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Reasonable Input to CMOS Inverter?
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Pass tr xor2 with inv restore
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Required to use? What take to use this with CMOS circuit?
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Restore Output Penn ESE370 Fall DeHon
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Restore Output Area? (compare to CMOS) Penn ESE370 Fall DeHon
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Chain Together Penn ESE370 Fall DeHon
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Analyze Stage Penn ESE370 Fall DeHon
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Inverter Delay Delay driving another inverter? Elmore
Include Cdiff=gCgate W=1 Penn ESE370 Fall DeHon
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Analyze Stage Penn ESE370 Fall DeHon
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Delay B=1? Penn ESE370 Fall DeHon
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Delay B=0? Penn ESE370 Fall DeHon
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CMOS Elmore and Cdiff Penn ESE370 Fall DeHon
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Identify Capacitances
Self output load? Load presented by A input? Capacitance between pd transistors? Penn ESE370 Fall DeHon
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Identify Capacitances
Which transistors on? Equivalent RC circuit (output stage) A=B=0? Penn ESE370 Fall DeHon
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Total Delay Total delay of circuit? Penn ESE370 Fall DeHon
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Cascade Delay Delay of chain of n of these? (connect Y to A)
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Compare Delay? Area? Penn ESE370 Fall DeHon
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Idea There are other circuit disciplines
Can use pass transistors for logic Sometimes gives area or delay win Penn ESE370 Fall DeHon
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Admin Project Udit office hour today
Due: latest Saturday midnight Udit office hour today Q: need for extra office hours on Thursday? Midterm 2: Wednesday, Nov. 7th Say more on Friday Penn ESE370 Fall DeHon
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