1. Penn ESE370 Fall2014 -- DeHon 1 ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems Day 18: October 13, 2014 Energy and Power Basics

2. Previously Where capacitance arises What drives delay –How to optimize Penn ESE370 Fall2014 -- DeHon 2

3. Today Power Sources Static Capacitive Switching Short Circuit (Day 19) Penn ESE370 Fall2014 -- DeHon 3

4. Power P=I×V Tricky part: –Understanding I –(pairing with correct V) Penn ESE370 Fall2014 -- DeHon 4

5. Understanding Currents Penn ESE370 Fall2014 -- DeHon 5

6. Preclass 1 Vin vs. I pwr,gnd ? –0V –140mV –400mV –500mV –600mV –840mV –1V Penn ESE370 Fall2013 -- DeHon 6

7. Operating Modes Steady-State: What modes are the transistors in? –Vin=Vdd –Vin=Gnd What current flows in steady state? Penn ESE370 Fall2014 -- DeHon 7

8. Operating Modes Steady-State: Vin=Vdd –PMOS subthreshold –NMOS resistive Penn ESE370 Fall2014 -- DeHon 8

9. Static Power Where does I static come from? –Subthreshold leakage –(possibly) Gate-Drain leakage Penn ESE370 Fall2014 -- DeHon 9 Vin~=V dd

10. Data Dependent? How does value of input impact I static ? Penn ESE370 Fall2014 -- DeHon 10

11. Data Dependent? How does value of input impact I static ? Penn ESE370 Fall2014 -- DeHon 11

12. Static Power P=I×V What V should we use? Penn ESE370 Fall2014 -- DeHon 12

13. Power: During Switching P=IV Input switch 1  0 What’s V? What’s I? Where does I go? Penn ESE370 Fall2014 -- DeHon 13

14. Power: During Switching P=IV Input switch 1  0 Where does I go? –Vin=Gnd Penn ESE370 Fall2014 -- DeHon 14

15. Power: During Switching P=IV Input switch 1  0 Where does I go? –Vin=Gnd Penn ESE370 Fall2014 -- DeHon 15

16. Power: During Switching P=IV Where does I go? –Vin=Vdd/2 And Vdd>Vthn+|Vthp| Penn ESE370 Fall2014 -- DeHon 16

17. Power: During Switching P=IV Input switch 1  0 Penn ESE370 Fall2014 -- DeHon 17

18. Power: During Switching P=IV Input switch 0  1 What’s V? What’s I? Where does current flow? Penn ESE370 Fall2014 -- DeHon 18

19. Power: During Switching P=IV Input switch 0  1 Where does I go? –Vin=Vdd Penn ESE370 Fall2014 -- DeHon 19

20. Power: During Switching P=IV Input switch 0  1 Where does I go? –Vin=Vdd Penn ESE370 Fall2014 -- DeHon 20

21. Switching Currents Charge (discharge) output If both transistor on: –Current path from V dd to Gnd Penn ESE370 Fall2014 -- DeHon 21

22. Observe I changes over time Data dependent At least two components –I static – no switch –I switch – when switch Penn ESE370 Fall2014 -- DeHon 22

23. Switching Penn ESE370 Fall2014 -- DeHon 23

24. Switching Currents I switch (t) = I sc (t) + I dyn (t) I(t) = I static (t)+I switch (t) Penn ESE370 Fall2014 -- DeHon 24 I sc I static I dyn

25. Charging I dyn (t) – why changing? –I ds = f(V ds,V gs ) –and V gs, V ds changing Penn ESE370 Fall2014 -- DeHon 25

26. Look at Energy [focus on I dyn (t)] Penn ESE370 Fall2014 -- DeHon 26

27. Energy to Switch Penn ESE370 Fall2014 -- DeHon 27

28. Integrating Do we know what this is? Penn ESE370 Fall2014 -- DeHon 28

29. Capacitor Charge Do we know what this is? What is Q? Penn ESE370 Fall2014 -- DeHon 29

30. Capacitor Charge Penn ESE370 Fall2014 -- DeHon 30

31. Capacitor Charging Energy Penn ESE370 Fall2014 -- DeHon 31

32. Switching Power Every time output switches 0  1 pay: –E = CV 2 P dyn = (# 0  1 trans) × CV 2 / time # 0  1 trans = ½ # of transitions P dyn = (# trans) × ½CV 2 / time Penn ESE370 Fall2014 -- DeHon 32

33. Short Circuit Current (time permitting) Penn ESE370 Fall2014 -- DeHon 33

34. Short Circuit Power Between V TN and V dd -V TP –Both N and P devices conducting Roughly: Penn ESE370 Fall2013 -- DeHon 34

35. Peak Current Penn ESE370 Fall2013 -- DeHon 35 I peak around V dd /2 –If |V TN |=|V TP | and sized equal rise/fall

36. Short-Circuit Energy Penn ESE370 Fall2013 -- DeHon 36

37. Short-Circuit Energy Penn ESE370 Fall2013 -- DeHon 37

38. Short Circuit Energy Looks like a capacitance –Q=I×t –Q=CV Penn ESE370 Fall2013 -- DeHon 38

39. Short Circuit Energy and Power Every time switch –Also dissipate short-circuit energy: E = CV 2 –Different C = C sc –C cs “fake” capacitance (for accounting) Largely same dependence as charging Penn ESE370 Fall2013 -- DeHon 39

40. Ideas Three components of power –Static –Short-circuit –Charging P tot = P static + P sc + P dyn Penn ESE370 Fall2014 -- DeHon 40

41. Admin HW6 due Thursday –4def dynamic switching energy Tuesday 11am Talk by Herman Schmit Subversive Innovation Normal lecture Wednesday and Friday Penn ESE370 Fall2014 -- DeHon 41