Transcript ppt
ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems Day 23: October 24, 2014 Pass Transistor Logic: part 2 (Cascading without Buffers) 1 Penn ESE370 Fall2014 -- DeHon Previously 2 Penn ESE370 Fall2014 -- DeHon Two XOR Gates 3 Penn ESE370 Fall2014 -- DeHon Today • Pass Transistor Circuit – Output levels – Cascading • Series pass transistors? • Delay • Start on Distributed RC – Analyzing delay for pass-tr designs 4 Penn ESE370 Fall2014 -- DeHon Cascading Pass Transistors 5 Penn ESE370 Fall2014 -- DeHon Chain without Inverters • What if we did this? 6 Penn ESE370 Fall2014 -- DeHon Extract key path 7 Penn ESE370 Fall2014 -- DeHon t=0 (after Vin transition 10) 8 Penn ESE370 Fall2014 -- DeHon t=4t (after Vin transition 10) 9 Penn ESE370 Fall2014 -- DeHon t=∞ (after Vin transition 10) 10 Penn ESE370 Fall2014 -- DeHon Focus on Pass tr • Vgs? • Operation mode? • Current flow? 11 Penn ESE370 Fall2014 -- DeHon Voltage of Chain • What is voltage at output? 12 Penn ESE370 Fall2014 -- DeHon How compare • Compare 13 Penn ESE370 Fall2014 -- DeHon DC Analysis 14 Penn ESE370 Fall2014 -- DeHon DC Analysis – chain of 6 15 Penn ESE370 Fall2014 -- DeHon Conclude • Can chain any number of pass transistors and only drop a single Vth 16 Penn ESE370 Fall2014 -- DeHon Transient 17 Penn ESE370 Fall2014 -- DeHon Closeup 18 Penn ESE370 Fall2014 -- DeHon Inverter Sense 19 Penn ESE370 Fall2014 -- DeHon Capacitance • What is Capacitance per stage (@y)? 20 Penn ESE370 Fall2014 -- DeHon Delay Setup • What does RC circuit look like? 21 Penn ESE370 Fall2014 -- DeHon Pass TR Tree • What if we did this? 22 Penn ESE370 Fall2014 -- DeHon Path • What’s different about this? 23 Penn ESE370 Fall2014 -- DeHon Gate Cascade? • What are voltages? 24 Penn ESE370 Fall2014 -- DeHon Demonstration Circuit 25 Penn ESE370 Fall2014 -- DeHon SPICE • TODO show spice results of voltages 26 Penn ESE370 Fall2014 -- DeHon Demonstration Chain 27 Penn ESE370 Fall2014 -- DeHon Spice 28 Penn ESE370 Fall2014 -- DeHon Transient Response 29 Penn ESE370 Fall2014 -- DeHon Conclude • Cannot cascade degraded inputs into gates. 30 Penn ESE370 Fall2014 -- DeHon Distribute RC (setup) Time Permitting 31 Penn ESE370 Fall2014 -- DeHon What is response? 32 Penn ESE370 Fall2014 -- DeHon What is response? 33 Penn ESE370 Fall2014 -- DeHon What is response? 34 Penn ESE370 Fall2014 -- DeHon SPICE Response 35 Penn ESE370 Fall2014 -- DeHon Intuition • Look at series of R’s on path – Must move Q=V(SC) across each R • Not as much as if both R’s precede C’s 36 Penn ESE370 Fall2014 -- 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 37 Penn ESE370 Fall2014 -- DeHon Admin • Project – Milestone 1 in – Will try to get feedback Friday evening/Sat. – Should be working hard on project – Rewarding experience 38 Penn ESE370 Fall2014 -- DeHon