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Signal Integrity Introduction
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What is Signal Integrity (SI)?
An Engineering PracticeThat ensures all signals transmitted arereceived correctly
That ensures signals dont interfere with
one another in a way to degrade reception. That ensures signal dont damage any
device
That ensures signal dont pollute theelectromagnetic spectrum
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Whats this all about?
$
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The Business
Determine design parameters forsuccessful signaling
Design parameters are ranges fordesign variables within which aproduct can be reliably built One in row is not good enough
New TermsGeneral SolutionPoint Solution
Specific Solution
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SI Paradigms
Specific Solution Applies to a given instance of a product or specimen
Point Solution
Applies to any single given product Encompasses a locus of specific solutions.
Example: Any board that comes off a production line
General Solution
Applies to many products of a given type Encompasses a locus of point solutions
The locus of all solutions for a specific standard (likeSCSI) is an example.
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Effective SI is Pre-Product Release.
It costs less here.
Why? Time = $
0
10
20
3040
50
Cost of
failure
(M$)
Pre-prototype
Validation Post Release
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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 each generation oftechnology (higher frequencies)
SI encompasses a conglomerate of electrical engineeringdisciplines
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
Validation
What is good enough?
Sufficient to operate at desired frequency with
required fidelity
Risk Assessment
SI i C Th 60 d
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SI in Computers The 60s and
70s
7400 Class TTL
Several MHz operation and 5ns edges
Transistor -Transistor Logic
Logic design with jelly bean ICs
Using loading rules from spec books
Lots of combinational and asynchronous one-shot designs.
Bipolar and CMOS
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The 60s and 70s - Continued
ECL Emitter Coupled Logic
Tens of MHz and 2-3ns edge rates
MECL hand bookOne of the first books on SI
Introduced concept of termination and transmission lines
Still used spec books for rules
A few engineers evaluated termination schemes but no
SI engineering per se
Common SI problems were deglitching switches
and specifying clamping diodes on relay drivers.
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The 80s
Hi Speed CMOS and open drain buses
100+ MHz operation and 1ns edges
Clocking issues start to creep in here
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 lines whosecharacteristics are extracted directly from PWB layout information
IBIS becomes popular
Edge rates move toward 300ps at launch.
Memory and I/O buses require early SI analysis
SSTLseries stub terminated AGTLAdvanced Gunning Transistor Logic
Open collector busing
Differential signaling emerges
Late in the decade we start to hear terms like return path, I/Opower delivery, ISI, and source-synch Extracted board simulators dont account for these
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The 00s
GHz operation and 50ps launch edges SI Engineers using spice and modeling with
Maxwell 2D/3-D field solvers.
Emerging technologiesHigh Speed Serial Differential
De/Pre emphasis
Embedded clockingData encoding
Pulse 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 of space.
Determine a rationale for specifying physical wiring length
in computer printed wiring boards. This is an exercise in
engineering judgment.
Plot the ratio of electrical edge length to board trace length
(by decade) in previous slide. Use range plots.
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SI Directions Today
SI is starting to borrow from the
communications industry
We are starting to hear terms likeVector Network Analyzer (VNA)
S-parameters
Return 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 performanceto determine rules for design
Use margin budgets to manage designs
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SI Deliverables
SI Customer
Product
Architect
Product
Designer
Product
Manager
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 enoughfascinatingtopics Can we still use transmission line models?
What is the role of ground? Higher and higher frequency
Underscores the need to understand 2nd and 3rd ordereffects.
List examples Many EE disciplines play together
Plethora of new signal analysis and measurement methods
Need to simplify designs to efficiently turn a profit.