1. Penn ESE370 Fall2011 -- DeHon 1 ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems Day 22: October 31, 2011 Pass Transistor Logic

2. Teaser What does this do? Penn ESE370 Fall2011 -- DeHon 2

3. Previously Penn ESE370 Fall2011 -- DeHon 3

4. Elmore Delay For each resistor Ri in path –Compute C Ri = sum of all C’s downstream of Ri –Delay through Ri is Ri×C Ri Penn ESE370 Fall2011 -- DeHon 4

5. Capacitance Roundup C GS =C GCS +C O C GD =C GCD +C O C GB =C GCB C SB =C diff C DB =C diff Penn ESE370 Fall2011 -- DeHon 5 Day 11

6. Impact on Capacitance Penn ESE370 Fall2011 -- DeHon 6

7. Contact/Diffusion Capacitance C j – diffusion depletion C jsw – sidewall capacitance L S – length of diffusion Penn ESE370 Fall2011 -- DeHon 7 LSLS

8. Today Elmore Delay with C diff >0 for CMOS Pass Transistor Circuit? –Output levels –Cascading Series pass transistors? Delay –Level Restore Penn ESE370 Fall2011 -- DeHon 8

9. CMOS Elmore and Cdiff Penn ESE370 Fall2011 -- DeHon 9

10. Identify Function What function? Penn ESE370 Fall2011 -- DeHon 10

11. Inverter Delay Delay driving self? –Elmore –Include Cdiff=  Cgate Penn ESE370 Fall2011 -- DeHon 11 W=1

12. Identify Capacitances Self output load? Load presented by A input? Capacitance between pd transistors? Penn ESE370 Fall2011 -- DeHon 12

13. Identify Capacitances Equivalent RC circuit (output stage) A=B=0? Penn ESE370 Fall2011 -- DeHon 13

14. Total Delay Total delay of circuit? Penn ESE370 Fall2011 -- DeHon 14

15. Cascade Delay Delay of chain of n of these? (connect Y to A) Penn ESE370 Fall2011 -- DeHon 15

16. Pass Transistor Penn ESE370 Fall2011 -- DeHon 16

17. Area Compare with CMOS circuit? Penn ESE370 Fall2011 -- DeHon 17

18. Output What does output look like (DC transfer)? Penn ESE370 Fall2011 -- DeHon 18

19. Pass TR transfer (B=1) Penn ESE370 Fall2011 -- DeHon 19

20. CMOS Inverter Transfer Penn ESE370 Fall2011 -- DeHon 20

21. Reasonable Input to CMOS Inverter? Penn ESE370 Fall2011 -- DeHon 21

22. Pass tr xor2 with inv restore Penn ESE370 Fall2011 -- DeHon 22

23. Required to use? What take to use this with CMOS circuit? Penn ESE370 Fall2011 -- DeHon 23

24. Restore Output Penn ESE370 Fall2011 -- DeHon 24

25. Chain Together Penn ESE370 Fall2011 -- DeHon 25

26. Analyze Stage Penn ESE370 Fall2011 -- DeHon 26

27. Analyze Stage Equivalent circuit? Delay? Compare area and timing to CMOS Penn ESE370 Fall2011 -- DeHon 27

28. Class ended here Penn ESE370 Fall2011 -- DeHon 28

29. Cascading Pass Transistors Penn ESE370 Fall2011 -- DeHon 29

30. Chain without Inverters What if we did this? Penn ESE370 Fall2011 -- DeHon 30

31. Extract key path Penn ESE370 Fall2011 -- DeHon 31

32. Voltage of Chain What is voltage at output? Penn ESE370 Fall2011 -- DeHon 32

33. How compare Compare Penn ESE370 Fall2011 -- DeHon 33

34. DC Analysis Penn ESE370 Fall2011 -- DeHon 34

35. DC Analysis – chain of 6 Penn ESE370 Fall2011 -- DeHon 35

36. Conclude Can chain any number of pass transistors and only drop a single Vth Penn ESE370 Fall2011 -- DeHon 36

37. Capacitance What is Capacitance per stage? Penn ESE370 Fall2011 -- DeHon 37

38. Delay Delay as a function of chain length? Penn ESE370 Fall2011 -- DeHon 38

39. Compare CMOS Buffered Pass TR Unbuffered Pass TR Delay Area Penn ESE370 Fall2011 -- DeHon 39

40. Pass TR Tree What if we did this? Penn ESE370 Fall2011 -- DeHon 40

41. Path What’s different about this? Penn ESE370 Fall2011 -- DeHon 41

42. Demonstration Circuit Penn ESE370 Fall2011 -- DeHon 42

43. SPICE TODO show spice results of voltages Penn ESE370 Fall2011 -- DeHon 43

44. Demonstration Chain Penn ESE370 Fall2011 -- DeHon 44

45. Spice Penn ESE370 Fall2011 -- DeHon 45

46. Conclude Cannot cascade degraded inputs into gates. Penn ESE370 Fall2011 -- DeHon 46

47. Admin Project –Due Friday Midterm 2: Nov. 9 th –Week from Wednesday in the evening Penn ESE370 Fall2011 -- DeHon 47

48. 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 Penn ESE370 Fall2011 -- DeHon 48