Signal Integrity Introduction Class 1

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Signal Integrity IntroductionClass 1

• Reduction To Practice for High Speed
  Digital Design
• Reading assignment CH8 to 9.3

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What is Signal Integrity (SI)?

• An Engineering Practice
• That ensures all signals transmitted are received
  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 the
  electromagnetic spectrum

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Whats this all about?

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The Business

• Determine design parameters for successful
  signaling
• Design parameters are ranges for design variables
  within which a product can be reliably built
• One in row is not good enough
• New Terms
• General Solution
• Point Solution
• Specific Solution

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Levels of SI Spheres of Influence
Specific Solution
One Box End User
Point Solution
Boxed ProductProviders
General Solution
Silicon Providers
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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 (like SCSI) is an example.

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Effective SI is Pre-Product Release.

• It costs less here.
• Why?
• Time

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Signal Integrity Paced by Silicon Advances

• Moores Law
• Still true
• Silicon densitydoubles every18 months
• Core frequency increase roughly follows density
• Data transfer rate of connected I/O
• Used to lag by about generation

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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)

• Transmitter

• Receiver

• Interconnect

Core IC logic
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Components of High Speed Design

• Transmitter

• Receiver

• Interconnect

• Transistors
• Passives
• Algorithms
• Memory

• Circuit elements
• Transmission lines
• S parameter blocks (advanced topic)

• Transistors
• Sources
• Algorithms
• Passives
• Memory

• Competitive performance goals challenge each
  generation of technology (higher frequencies)
• SI encompasses a conglomerate of electrical
  engineering disciplines

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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

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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 book One 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 whose characteristics 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
• 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-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 2½D/3-D field solvers.
• Emerging technologies
• High Speed Serial Differential
• De/Pre emphasis
• Embedded clocking
• Data 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 like
• Vector 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 performance to
  determine rules for design
• Use margin budgets to manage designs

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SI Deliverables
Assignment Fill in the above 6 boxes with
hypothetical examples based on your present
knowledge of the computer engineering field.
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Future of SI

• Rules of thumb get old quick
• Old assumptions not good enough fascinating
  topics
• 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
  order effects.
• List examples
• Many EE disciplines play together
• Plethora of new signal analysis and measurement
  methods
• Need to simplify designs to efficiently turn a
  profit.