Richard Mellitz1 Signal Integrity Introduction Class 1 Reduction To Practice for High Speed Digital Design Reading assignment: CH8 to 9.3

2 Introduction – Richard Mellitz 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

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

4 Introduction – Richard Mellitz 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

5 Introduction – Richard Mellitz Levels of SI Spheres of Influence Silicon Providers Boxed Product Providers One Box – End User

6 Introduction – Richard Mellitz 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.

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

8 Introduction – Richard Mellitz Signal Integrity Paced by Silicon Advances  “Moore’s Law” Still true Silicon density doubles every 18 months  “Core” frequency increase roughly follows density  Data transfer rate of connected I/O Used to lag by about generation

9 Introduction – Richard Mellitz 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 Interconnect Receiver

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

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

12 Introduction – Richard Mellitz 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

13 Introduction – Richard Mellitz 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.

14 Introduction – Richard Mellitz 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

15 Introduction – Richard Mellitz 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

16 Introduction – Richard Mellitz 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)

17 Introduction – Richard Mellitz 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.

18 Introduction – Richard Mellitz 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

19 Introduction – Richard Mellitz 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

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

21 Introduction – Richard Mellitz 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 2 nd and 3 rd 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.