Signal Integrity Introduction
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
Whats this all about?
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
Levels of SI Spheres of Influence
One Box End User Boxed Product Providers Silicon Providers
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.
Effective SI is Pre-Product Release.
It costs less here.
50 40 Cost of failure (M$) 30 20 10 0 Preprototype Validation Post Release
Why?
Time = $
Signal Integrity Paced by Silicon Advances
Moores Law
Still true Silicon density doubles every 18 months
31 26
Density Multiplier
21
16
11
1 Apr-01 Sep-02 Jan-04 May-05 Oct-06 Feb-08 Jul-09
Core frequency increase roughly follows density Data transfer rate of connected I/O
Used to lag by about generation
What About Design Functionality?
Normally not the domain of SI Often qualifies legal operation For most computers I/O signals are v(t)
Transmitter Interconnect
Receiver
Core: IC logic
Components of High Speed Design
Transmitter Receiver Interconnect
Transistors Sources Algorithms Passives Memory
Circuit elements Transmission lines S parameter blocks (advanced topic)
Transistors Passives Algorithms Memory
Competitive performance goals challenge each generation of technology (higher frequencies) SI encompasses a conglomerate of electrical engineering disciplines
SI Work
Modeling Simulation Measurement Validation What is good enough?
Sufficient to operate at desired frequency with required fidelity
Risk Assessment
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 oneshot designs. Bipolar and CMOS
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.
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
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
The 00s
GHz operation and 50ps launch edges SI Engineers using spice and modeling with Maxwell 2D/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)
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.
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
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
SI Deliverables
Product SI Customer Architect
"What if ? "
Product Designer
Rules
Product Manager
Use measurement to ensure confidence in simulations decisions
Deliverables
Feasibility
Assignment: Fill in the above 6 boxes with hypothetical examples based on your present knowledge of the computer engineering field.
Cost/Performance No Field Failures Tradeoff
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.
