1. Penn ESE370 Fall2011 -- DeHon 1 ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems Day 2: September 9, 2011 Transistor Introduction

2. Today MOSFET Capacitive and resistive loads Zero-th order transistor model –Good enough for [what?] Diagnostic Quiz (12:40pm) Penn ESE370 Fall2011 -- DeHon 2

3. MOSFET Metal Oxide Semiconductor Field Effect Transistor –New device –Primary active component for the term –Three terminal device Voltage at gate controls conduction between two other terminals (source, drain) Penn ESE370 Fall2011 -- DeHon 3

4. MOSFET I vs. Vgs, Vds Penn ESE370 Fall2011 -- DeHon 4 I DS

5. MOSFET I vs. Vgs, Vds Will dig into understanding during term Today: simple ways to reason about gross behavior –Static/DC Penn ESE370 Fall2011 -- DeHon 5

6. Preclass What voltage do the cases converge to? Penn ESE370 Fall2010 -- DeHon 6

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11. Conclude? DC/Steady-State –Ignore the capacitors Penn ESE370 Fall2010 -- DeHon 11

12. Quasistatic Static – inputs (and circuit) unchanging, how does it settle? Dynamic – what happens when things change Quasi-Static – inputs transition, circuit responds, and settles –Dynamic transition to roughly static states Penn ESE370 Fall2011 -- DeHon 12

13. Quasistatic Relevance? How relevant to a combinational digital circuit? How relevant to a clocked digital circuit? Penn ESE370 Fall2011 -- DeHon 13

14. Zero-th Order MOSFET Ideal Switch Vgs > Vth  conducts Vgs < Vth  does not conduct Vth – threshold voltage Gate draws no current from input –Loads input capacitively Penn ESE370 Fall2011 -- DeHon 14

15. Zero-th Order MOSFET Penn ESE370 Fall2011 -- DeHon 15 I DS

16. N-Type, P-Type MOSFET N – negative carriers –electrons Switch turned on positive Vgs P – positive carriers –holes Switch turned on negative Vgs Penn ESE370 Fall2011 -- DeHon 16 Vthp<0 Vgs<Vthp to to conduct

17. Symmetry Device is symmetric Doesn’t know source from drain Think of it as a resistor: –Also doesn’t know difference between two ends –Which way does current flow? N-type: –Electrons are carriers –Electrons charged? negative –Electrons flow from src  drain –From which voltage? Lowest voltage  highest –Drain is ? most positive terminal Penn ESE370 Fall2011 -- DeHon 17

18. Symmetry Device is symmetric Doesn’t know source from drain Think of it as a resistor: –Which way does current flow? P-type: –Holes are carries –Holes charged how? positively –Holes flow from src  drain –From which voltage? Highest voltage  lowest –Drain is? most negative terminal Penn ESE370 Fall2011 -- DeHon 18

19. Zero-th Order MOSFET Penn ESE370 Fall2011 -- DeHon 19 I DS

20. Why zero-order useful? Penn ESE370 Fall2011 -- DeHon 20

21. What happens when Vin=Vdd>Vthn Penn ESE370 Fall2011 -- DeHon 21 Vthp=-Vthn

22. What happens when Vin=Vdd>Vth Penn ESE370 Fall2011 -- DeHon 22 Vgs=Vdd > Vthn Vthp=-Vthn

23. What happens when Vin=Vdd>Vth Penn ESE370 Fall2011 -- DeHon 23 Vgs=Vdd > Vth Vthp=-Vthn

24. What happens when Vin=Vdd>Vth Penn ESE370 Fall2011 -- DeHon 24 Vgs=Vdd > Vth Vgs=0 > Vthp Vthp=-Vthn

25. What happens when Vin=Vdd>Vth Penn ESE370 Fall2011 -- DeHon 25 Vgs=Vdd > Vthn Vgs=0 > Vthp Vthp=-Vthn

26. What happens when Vin=Vdd>Vth Penn ESE370 Fall2011 -- DeHon 26 Vgs=Vdd > Vthn Vgs=0 > Vthp V2=Gnd Vthp=-Vthn

27. What happens when Vin=Vdd>Vth Penn ESE370 Fall2011 -- DeHon 27 Vgs=Vdd > Vthn Vgs=0 > Vthp V2=Gnd Vgs=0 < Vthn Vthp=-Vthn

28. What happens when Vin=Vdd>Vth Penn ESE370 Fall2011 -- DeHon 28 Vgs=Vdd > Vthn Vgs=0 > Vthp V2=Gnd Vgs=0 < Vthn Vthp=-Vthn

29. What happens when Vin=Vdd>Vth Penn ESE370 Fall2011 -- DeHon 29 Vgs=Vdd > Vthn Vgs=0 > Vthp V2=Gnd Vgs=0 < Vthn Vgs=-Vdd < Vthp Vout=Vdd Vthp=-Vthn

30. What happens when Vin=0<Vth Penn ESE370 Fall2011 -- DeHon 30 Work on board

31. What happens when Vin=0<Vth Penn ESE370 Fall2011 -- DeHon 31 V2=Vdd Vout=0

32. What function? Buffer Vin=Vdd  Vout=Vdd Vin=0  Vout=0 Penn ESE370 Fall2011 -- DeHon 32

33. Why Zeroth Order Useful? Allows us to reason (mostly) at logic level about steady-state functionality of typical gate circuits Make sure understand logical function (achieve logical function) before worrying about performance details Penn ESE370 Fall2011 -- DeHon 33

34. Why adequate? Static analysis – can ignore capacitors Capacitive loads – resistances don’t matter Feed forward for gates – –don’t generally have loops –can work forward from known values Logic drive rail-to-rail –Don’t have to reason about intermediate voltage levels Penn ESE370 Fall2011 -- DeHon 34

35. What not tell us? Delay Dynamics Behavior if not –Capacitively loaded –Acyclic (if there are Loops) –Rail-to-rail drive Penn ESE370 Fall2011 -- DeHon 35

36. Admin Piazza  should have received mail from Paul Gurniak HW1 posted  due next Friday –…important to lab next Friday Penn ESE370 Fall2011 -- DeHon 36

37. Big Ideas MOSFET Transistor as switch Purpose-driven simplified modeling –Aid reasoning –Sanity check –Simplify design Penn ESE370 Fall2011 -- DeHon 37

38. Diagnostic Quiz Turnin Quiz and feedback before leaving (do not turnin preclass  keep that) Penn ESE370 Fall2011 -- DeHon 38