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Signal Integrity IntroductionClass 1

Reduction To Practicefor High Speed Digital Design

Reading assignment: CH8 to 9.3

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What is Signal Integrity (SI)?

An Engineering PracticeThat ensures all signals transmitted

are received correctlyThat ensures signals dont interfere

with one another in a way to degradereception.That ensures signal dont damage anydevice

That ensures signal dont pollute theelectromagnetic spectrum

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Whats this all about?

$

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The BusinessDetermine design parameters for

successful signalingDesign parameters are ranges for

design variables within which a

product can be reliably builtOne in row is not good enoughNew Terms

General SolutionPoint SolutionSpecific Solution

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Levels of SI Spheres of Influence

Silicon Providers

Boxed ProductProviders

One Box

End User

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SI Paradigms

Specific Solution

Applies to a given instance of a product orspecimen

Point SolutionApplies to any single given product

Encompasses a locus of specific solutions.Example: Any board that comes off a productionline

General Solution

Applies to many products of a given typeEncompasses a locus of point solutionsThe locus of all solutions for a specific standard(like SCSI) is an example.

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Effective SI is Pre-Product Release.

It costs less here.

Why?Time = $

0

10

20

30

40

50

Cost of

failure

(M$)

Pre-prototype

Validation Post Release

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Signal Integrity Paced by Silicon Advances

Moores LawStill true

Silicon densitydoubles every

18 months

Core frequency increase roughly

follows densityData transfer rate of connected I/O

Used to lag by about generation

1

6

11

16

21

26

31

Apr-01 Sep-02 Jan-04 May-05 Oct-06 Feb-08 Jul-09

DensityMultiplier

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What About Design Functionality?

Normally not the domain of SI Often qualifies legal operation

For most computers I/O signals are v(t)

Core: IC logic

Transmitter

InterconnectReceiver

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Components of High Speed Design

Competitive performance goals challenge eachgeneration of technology (higher frequencies)

SI encompasses a conglomerate of electricalengineering disciplines

Transmitter

Interconnect

Receiver

Circuit elements Transmission lines

S parameter blocks(advanced topic)

Transistors Sources Algorithms Passives Memory

Transistors Passives Algorithms Memory

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SI Work

Modeling

Simulation

Measurement

ValidationWhat is good enough?

Sufficient to operate at desiredfrequency with required fidelity

Risk Assessment

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SI in Computers The 60s and 70s

7400 Class TTLSeveral MHz operation and 5ns edges

Transistor -Transistor Logic

Logic design with jelly bean ICs

Using loading rules from spec booksLots of combinational and asynchronousone-shot designs.

Bipolar and CMOS

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The 60s and 70s - Continued

ECL

Emitter Coupled LogicTens of MHz and 2-3ns edge rates

MECL hand book One of the first books on SIIntroduced concept of termination and transmission

lines

Still used spec books for rules

A few engineers evaluated termination schemesbut no SI engineering per se

Common SI problems were deglitchingswitches and specifying clamping diodes onrelay drivers.

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The 80s

Hi Speed CMOS and open drainbuses

100+ MHz operation and 1ns edges

Clocking issues start to creep inhere

Ringing becomes a problem

Timing simulators emerge for SI

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The 90s

Early in the decade extracted board simulators are

popular.Chip I/V and edge V(t) info simulated with transmission lineswhose characteristics are extracted directly from PWBlayout informationIBIS becomes popular

Edge rates move toward 300ps at launch. Memory and I/O buses require early SI analysis SSTL series stub terminated AGTL Advanced Gunning Transistor Logic

Open collector busing Differential signaling emerges Late in the decade we start to hear terms like return

path, I/O power delivery, ISI, and source-synchExtracted board simulators dont account for these

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The 00s

GHz operation and 50ps launch edges

SI Engineers using spice and modelingwith Maxwell 2D/3-D field solvers.Emerging technologies

High Speed Serial DifferentialDe/Pre emphasisEmbedded clocking

Data encodingPulse Amplitude Modulation (PAM)Simultaneous Bi-Directional (SBD)

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Assignment

Assignment: How much electrical transmission length

does a 5ns, 2.5ns, 1ns, 300ps, 50ps edge occupy?Assume propagation velocity is half that free ofspace.

Determine a rationale for specifying physical wiring

length in computer printed wiring boards. This is anexercise in engineering judgment.

Plot the ratio of electrical edge length to boardtrace length (by decade) in previous slide. Use range

plots.

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SI Directions Today

SI is starting to borrow from thecommunications industryWe are starting to hear terms like

Vector Network Analyzer (VNA)

S-parametersReturn and insertion loss

Eye diagram

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SI Roles

Convert product parts and design features

into models and parameters Use models to simulate performance

Perform measurements to validate product

Determine how parameters limit performance Use cost and simulated or measured

performance to determine rules for design

Use margin budgets to manage designs

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SI Deliverables

SI Customer ProductArchitect ProductDesigner ProductManager

Deliverables

"What if ? " Rules

Use measurement

to ensure

confidence in

simulations

decisions

FeasibilityCost/Performance

TradeoffNo Field Failures

Assignment: Fill in the above 6 boxes with

hypothetical examples based on yourpresent knowledge of the computerengineering field.

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Future of SI Rules of thumb get old quick

Old assumptions not good enough fascinating topicsCan we still use transmission line models?What is the role of ground?

Higher and higher frequencyUnderscores the need to understand 2nd and 3rd

order effects.List examplesMany EE disciplines play together

Plethora of new signal analysis and measurementmethodsNeed to simplify designs to efficiently turn aprofit.