Transcript What is Signal Integrity?

Signal Integrity Introduction
Class 1
Reduction To Practice
for High Speed Digital Design
Reading assignment: CH8 to 9.3
Richard Mellitz
1
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
2
What’s this all about?
$
Introduction – Richard Mellitz
3
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
4
Levels of SI Spheres of Influence
One Box –
End User
Boxed Product
Providers
Silicon Providers
Introduction – Richard Mellitz
5
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
6
Effective SI is Pre-Product Release.
 It costs less here.
50
40
Cost of 30
failure
20
(M$)
10
0
Pre-
 Why?
Validation Post Release
prototype
Time = $
Introduction – Richard Mellitz
7
Signal Integrity Paced by Silicon Advances
 “Moore’s Law”
26
Density Multiplier
Still true
Silicon density
doubles every
18 months
31
21
16
11
6
1
Apr-01
Sep-02
Jan-04
May-05
Oct-06
Feb-08
 “Core” frequency increase roughly
Jul-09
follows density
 Data transfer rate of connected I/O
Used to lag by about generation
Introduction – Richard Mellitz
8
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
9
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
Introduction – Richard Mellitz
10
SI Work
 Modeling
 Simulation
 Measurement
 Validation
 What is good enough?
Sufficient to operate at desired
frequency with required fidelity
 Risk Assessment
Introduction – Richard Mellitz
11
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
12
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
13
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
14
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
The 00’s
16
 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
Assignment
17
 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
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
18
SI Roles
19
 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
Product
SI Customer Architect
Product
Designer
Product
Manager
"What if ? "
Rules
Use measurement
to ensure
confidence in
simulations
decisions
Feasibility
Cost/Performance
No Field Failures
Tradeoff
Deliverables
Assignment: Fill in the above 6 boxes with
hypothetical examples based on your
present knowledge of the computer
engineering field.
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 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
21