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Day 8: September 23, 2011 Delay and RC Response

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Presentation on theme: "Day 8: September 23, 2011 Delay and RC Response"— Presentation transcript:

1 Day 8: September 23, 2011 Delay and RC Response
ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems Day 8: September 23, 2011 Delay and RC Response Penn ESE370 Fall DeHon

2 Delay is RC Charging Penn ESE370 Fall DeHon

3 Delay is RC Charging Strategy Understand switch state
Break into stages For each stage Understand Rdrive Understand Cload Penn ESE370 Fall DeHon

4 Today RC Charging RC Step Response What is the C? What is the R?
Measuring Delay Penn ESE370 Fall DeHon

5 90% Rise Time? Penn ESE370 Fall DeHon

6 What does response look like?
about 2ps for 90% rise Penn ESE370 Fall DeHon

7 Governing Equations? (KCL)
Vmeasure? Current across Resistor? Current into Capacitor? Penn ESE370 Fall DeHon

8 Equations Penn ESE370 Fall DeHon

9 Solve Vmeasure What’s Vmeasure? Penn ESE370 Fall DeHon

10 What does look like? Penn ESE370 Fall DeHon

11 Shape of Curve x e-x 1-e-x Fillin on board 0.1 1 2 2.3
0.1 1 2 2.3 Penn ESE370 Fall DeHon

12 Shape of Curve x e-x 1-e-x 1 0.1 0.9 1/e = 0.37 0.66 2 1/e2 = 0.14
1 0.1 0.9 1/e = 0.37 0.66 2 1/e2 = 0.14 0.86 2.3 Penn ESE370 Fall DeHon

13 Risetime: 10—90% Trise ~= 2.2ps Penn ESE370 Fall DeHon

14 What is C? Penn ESE370 Fall DeHon

15 Capacitance Wire MOSFET gate Logical Gate Fanout -- Total gate load
Penn ESE370 Fall DeHon

16 First Order Model Switch As dig in, understand:
Loads input capacitively As dig in, understand: Origin of capacitance How can we engineer Tradeoffs Penn ESE370 Fall DeHon

17 Logic Gate Input Capacitance
Capacitance on A input? B input? Penn ESE370 Fall DeHon

18 Fanout in Circuit Output routed to many gate inputs
Penn ESE370 Fall DeHon

19 Fanout in Circuit Maximum fanout? Second? Min?
Penn ESE370 Fall DeHon

20 Lumped Capacitive Load
Penn ESE370 Fall DeHon

21 What is R? Penn ESE370 Fall DeHon

22 Resistance Wire resistance Transistor equivalent resistance
Supply to transistor source Transistor output gate it is driving Transistor equivalent resistance Penn ESE370 Fall DeHon

23 Wire Resistances Penn ESE370 Fall DeHon

24 First Order Model Switch As dig in, understand: Resistive driver
More sophisticated view How can we engineer Tradeoffs Penn ESE370 Fall DeHon

25 Equivalent Resistance
What resistances might transistors contribute? How many cases? Assume Ron same all tr, Resistance of each? Penn ESE370 Fall DeHon

26 Equivalent Resistance
What resistances might transistors contribute? Input Rout 00 Ron/2 01 Ron 10 11 2Ron Penn ESE370 Fall DeHon

27 Lumped Resistive Source
Rtrnet = parallel and series combination of Rtr Penn ESE370 Fall DeHon

28 Measuring Delay Penn ESE370 Fall DeHon

29 Measuring Gate Delay Next stage starts to switch before first finishes
Measure 50%--50% 67ps 80ps tdel = 13ps Penn ESE370 Fall DeHon

30 Characterizing Gate/Technology
Delay measure will be Function of load on gate Function of input rise time Which, in turn, may be a function of input loading Penn ESE370 Fall DeHon

31 Delay vs. Risetime 1ps rise 100ps rise 20ps delay 10ps delay
Penn ESE370 Fall DeHon

32 Characterizing Gate/Technology
Delay measure will be Function of load on gate Function of input rise time Which, in turn, may be a function of input loading Want to understand typical At least comparable Penn ESE370 Fall DeHon

33 Measuring/Characterizing
Drive with a gate Not an ideal source Measure loaded gate Typical loading – FO4 Penn ESE370 Fall DeHon

34 HW2 Recommendation Penn ESE370 Fall DeHon

35 Rise/Fall Rise and Fall time may differ Why? What is ratio? Input Rout
00 Ron/2 01 Ron 10 11 2Ron Penn ESE370 Fall DeHon

36 Admin HW3 posted Intel talk Wednesday (28th)
Penn ESE370 Fall DeHon

37 Delay is RC Charging Penn ESE370 Fall DeHon

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