Signal Integrity Introduction Class 1

1. Signal Integrity IntroductionClass 1 Reduction To Practice for High Speed Digital Design Reading assignment: CH8 to 9.3 Richard Mellitz

2. What is Signal Integrity (SI)? • An Engineering Practice • That ensures all signals transmitted are received correctly • That ensures signals don’t interfere with one another in a way to degrade reception. • That ensures signal don’t damage any device • That ensures signal don’t pollute the electromagnetic spectrum Introduction – Richard Mellitz

3. What’s this all about? $ Introduction – Richard Mellitz

4. 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 Introduction – Richard Mellitz

5. Levels of SI Spheres of Influence Specific Solution One Box – End User Point Solution Boxed ProductProviders General Solution Silicon Providers Introduction – Richard Mellitz

6. 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. Introduction – Richard Mellitz

7. Effective SI is Pre-Product Release. • It costs less here. • Why? • Time = $ Introduction – Richard Mellitz

8. Signal Integrity Paced by Silicon Advances • “Moore’s 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 Introduction – Richard Mellitz

9. 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 Introduction – Richard Mellitz

10. Components of High Speed Design • Competitive performance goals challenge each generation of technology (higher frequencies) • SI encompasses a conglomerate of electrical engineering disciplines • Transmitter • Receiver • Interconnect • Transistors • Passives • Algorithms • Memory • Transistors • Sources • Algorithms • Passives • Memory • Circuit elements • Transmission lines • S – parameter blocks (advanced topic) Introduction – Richard Mellitz

11. SI Work • Modeling • Simulation • Measurement • Validation • What is good enough? • Sufficient to operate at desired frequency with required fidelity • Risk Assessment Introduction – Richard Mellitz

12. SI in Computers – The 60’s and 70’s • 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 Introduction – Richard Mellitz

13. The 60’s and 70’s - 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. Introduction – Richard Mellitz

14. The 80’s • 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 Introduction – Richard Mellitz

15. The 90’s • 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 don’t account for these Introduction – Richard Mellitz

16. The 00’s • 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) Introduction – Richard Mellitz

17. 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. Introduction – Richard Mellitz

18. 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 Introduction – Richard Mellitz

19. 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 Introduction – Richard Mellitz

20. SI Deliverables Assignment: Fill in the above 6 boxes with hypothetical examples based on your present knowledge of the computer engineering field. Introduction – Richard Mellitz

21. 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. Introduction – Richard Mellitz