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EE4271 VLSI Design

VLSI Routing

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Routing Problem

Routing to reduce the area

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Metal layer 1

Via

Routing Anatomy

Topview

3Dview

Metal layer 2

Metal layer 3

Sym

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Layou

t

©Bazargan

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Routing Grid

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Channel Routing Terminology

Upper boundaryUpper boundary

Lower boundaryLower boundary

TracksTracks

Terminals (Gate Pins)Terminals (Gate Pins)ViaVia

WidthWidth

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Channel Routing Problem - I

• Input: – Two vectors of the same length to represent the pins on two

sides of the channel.– One horizontal layer and one vertical layer

• Output:– Connect pins of the same net together.– Minimize the channel width.– Minimize the number of vias.

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Channel Routing Problem - II

00 11 22 22 00 33 00 44

11 22 00 33 33 44 44 00

Example: (01220304) (12033440)where 0 = no terminal

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A Channel Routing Example

0 1 4 5 1 6 7 0 4 9 10 10

2 3 5 3 5 2 6 8 9 8 7 9

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The Other Example

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Lower Bound on Channel Width00 11 66 11 22 33 55

66 33 55 44 00 22 44

00 11 66 11 22 33 55

66 33 55 44 00 22 44

11 2233

55 4466

LocalLocaldensitydensity 11 33 44 44 44 44 22

Channel density =Channel density =Maximum local densityMaximum local density

Lower bound = 4Lower bound = 4

Lower bound on channel width = Channel density

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A More Complex Example

# columns =174, # nets=72, density =19

Routing result:number of tracks=20

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Realistic Design

From DAC Knowledge CenterDifferent colors refer to different wire densities.

Red color means congestion.