lecture21 - Lecture 21 Interconnect Modeling EECS 312...

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EECS 312 1 Lecture 21: Interconnect Modeling EECS 312 Reading: 4.3.2 (ignore skin effect), 4.4 (ignore 4.4.5), 9.3.3
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Last Time EECS 312 2 • Wiring capacitance is the main parasitic – Slows things down, can also cause noise problems (next time) – Can be comparable to device capacitances! – Area, fringing, interwire components – Interwire dominates today – Both simple and complex models exist to compute capacitance as a function of wire geometry
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Lecture Overview EECS 312 3 • RC delay models • Repeaters
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EECS 312 4 Evolution of Interconnect Modeling Before 1990, wires were thick and wide while devices were big and slow – Large wiring capacitances and device resistances – Wiring resistance was << device resistance – Model wires as capacitances only In the 1990s, scaling theory led to smaller and faster devices and smaller, more resistive wires Reverse Scaling properties of wires! – RC models became necessary In the 2000s, frequencies are high enough so that inductance is a major component of total impedance
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Lumped RC model of a wire EECS 312 5
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The Elmore Delay EECS 312 6
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RC Delay EECS 312 7
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RC Models EECS 312 8
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RC Propagating Wavefront EECS 312 9 Step response of a distributed RC wire as a function of location along wire and time
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Delay expressions EECS 312 10 Assumes step input Vin 2 38 . 0 69 . 0 L c r L c R t w w w s p + = () L w w w L w s p LC r L c r C L c R t 69 . 0 38 . 0 69 . 0 2 + + + = We will typically have a load capacitance C L at node V out () L w w w L w s p LC r L c r C C L c R t 69 . 0 38 . 0 69 . 0 2 int + + + + = Finally, let’s include the intrinsic driver capacitance, C int
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How to reduce RC delay EECS 312 11 • Since RC delay is quadratic with length, reducing length is key • Note: 2 2 = 4 and 1+1 = 2 but 1 2 + 1 2 = 2 driver receiver driver receiver L = 2 units
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This note was uploaded on 04/01/2008 for the course EECS 312 taught by Professor Maharbiz during the Fall '07 term at University of Michigan.

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lecture21 - Lecture 21 Interconnect Modeling EECS 312...

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