Transcript ppt - SEAS
ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems Day 22: October 31, 2011 Pass Transistor Logic 1 Penn ESE370 Fall2011 -- DeHon Teaser • What does this do? 2 Penn ESE370 Fall2011 -- DeHon Previously 3 Penn ESE370 Fall2011 -- DeHon Elmore Delay • For each resistor Ri in path – Compute CRi = sum of all C’s downstream of Ri – Delay through Ri is Ri×CRi Delay R C j i p a th path i j 4 Penn ESE370 Fall2011 -- DeHon Day 11 Capacitance Roundup • • • • • CGS=CGCS+CO CGD=CGCD+CO CGB=CGCB CSB=Cdiff CDB=Cdiff 5 Penn ESE370 Fall2011 -- DeHon Impact on Capacitance 6 Penn ESE370 Fall2011 -- DeHon Contact/Diffusion Capacitance • Cj – diffusion depletion • Cjsw – sidewall capacitance • LS – length of diffusion Cdiff Cdiff 0W LS Cdiff C j LSW C jsw 2LS W 7 Penn ESE370 Fall2011 -- DeHon Today • Elmore Delay with Cdiff>0 for CMOS • Pass Transistor Circuit? – Output levels – Cascading • Series pass transistors? • Delay – Level Restore 8 Penn ESE370 Fall2011 -- DeHon CMOS Elmore and Cdiff 9 Penn ESE370 Fall2011 -- DeHon Identify Function • What function? 10 Penn ESE370 Fall2011 -- DeHon Inverter Delay • Delay driving self? – Elmore – Include Cdiff=gCgate W=1 11 Penn ESE370 Fall2011 -- DeHon Identify Capacitances • Self output load? • Load presented by A input? • Capacitance between pd transistors? 12 Penn ESE370 Fall2011 -- DeHon Identify Capacitances • Equivalent RC circuit (output stage) A=B=0? 13 Penn ESE370 Fall2011 -- DeHon Total Delay • Total delay of circuit? 14 Penn ESE370 Fall2011 -- DeHon Cascade Delay • Delay of chain of n of these? (connect Y to A) 15 Penn ESE370 Fall2011 -- DeHon Pass Transistor 16 Penn ESE370 Fall2011 -- DeHon Area • Compare with CMOS circuit? 17 Penn ESE370 Fall2011 -- DeHon Output • What does output look like (DC transfer)? 18 Penn ESE370 Fall2011 -- DeHon Pass TR transfer (B=1) 19 Penn ESE370 Fall2011 -- DeHon CMOS Inverter Transfer 20 Penn ESE370 Fall2011 -- DeHon Reasonable Input to CMOS Inverter? 21 Penn ESE370 Fall2011 -- DeHon Pass tr xor2 with inv restore 22 Penn ESE370 Fall2011 -- DeHon Required to use? • What take to use this with CMOS circuit? 23 Penn ESE370 Fall2011 -- DeHon Restore Output 24 Penn ESE370 Fall2011 -- DeHon Chain Together 25 Penn ESE370 Fall2011 -- DeHon Analyze Stage 26 Penn ESE370 Fall2011 -- DeHon Analyze Stage • Equivalent circuit? • Delay? • Compare area and timing to CMOS 27 Penn ESE370 Fall2011 -- DeHon Class ended here 28 Penn ESE370 Fall2011 -- DeHon Cascading Pass Transistors 29 Penn ESE370 Fall2011 -- DeHon Chain without Inverters • What if we did this? 30 Penn ESE370 Fall2011 -- DeHon Extract key path 31 Penn ESE370 Fall2011 -- DeHon Voltage of Chain • What is voltage at output? 32 Penn ESE370 Fall2011 -- DeHon How compare • Compare 33 Penn ESE370 Fall2011 -- DeHon DC Analysis 34 Penn ESE370 Fall2011 -- DeHon DC Analysis – chain of 6 35 Penn ESE370 Fall2011 -- DeHon Conclude • Can chain any number of pass transistors and only drop a single Vth 36 Penn ESE370 Fall2011 -- DeHon Capacitance • What is Capacitance per stage? 37 Penn ESE370 Fall2011 -- DeHon Delay • Delay as a function of chain length? 38 Penn ESE370 Fall2011 -- DeHon Compare • CMOS • Buffered Pass TR • Unbuffered Pass TR • Delay • Area 39 Penn ESE370 Fall2011 -- DeHon Pass TR Tree • What if we did this? 40 Penn ESE370 Fall2011 -- DeHon Path • What’s different about this? 41 Penn ESE370 Fall2011 -- DeHon Demonstration Circuit 42 Penn ESE370 Fall2011 -- DeHon SPICE • TODO show spice results of voltages 43 Penn ESE370 Fall2011 -- DeHon Demonstration Chain 44 Penn ESE370 Fall2011 -- DeHon Spice 45 Penn ESE370 Fall2011 -- DeHon Conclude • Cannot cascade degraded inputs into gates. 46 Penn ESE370 Fall2011 -- DeHon Admin • Project – Due Friday • Midterm 2: Nov. 9th – Week from Wednesday in the evening 47 Penn ESE370 Fall2011 -- DeHon Idea • There are other circuit disciplines • Can use pass transistors for logic – Even chains of pass transistors – Sometimes gives area or delay win • Do not cascade as easily as CMOS 48 Penn ESE370 Fall2011 -- DeHon