Tektronix Confidential1
Signal Integrity Analysisof Gigabit Interconnects
Olie Kreidler Tektronix, Inc.
Tektronix Confidential2
Signal Integrity (SI): Digital Becomes Analog
“At high frequencies … crosstalk and signal reflections can be perceived as logic triggers, and can be responsible for erroneous signal patterns”
– EE Times, April 17, 1998, Special Section on Interconnects
Tektronix Confidential3
Industry Trends and Issues
On-going trends and issues– Trends: faster rise times, clock frequencies, increasing
interconnect complexity– Requirement: increasing need for signal integrity analysis and
SPICE / IBIS interconnect modeling
New trends and requirements– Trends:
S-parameters and eye diagrams are becoming part of compliance testing for passive PHY
All standards currently are differential and serial– Requirements
Eye diagram and S-parameter compliance testing must be performed in differential mode
Frequency dependent losses need to be modeled
Tektronix Confidential4
Outline
Interconnect Measurement Accuracy Issues TDR/T and VNA Measurement Basics
App Note: “TDR and VNA Measurement Primer”– Impedance Measurements and IConnect® True Impedance
Profile – Time Domain S-parameter Measurements– Eye Diagram Measurements – TDR Probing and Fixturing
2007/06/10 Confidential V1.15
High-Speed Serial Data Link Analysis The Measurement Challenge - A Closed Eye
An “Open Eye” at the Transmitter
a “Closed Eye” at the Receiver
How to measure this eye?
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Rcv
EQ
UA
LIZ
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Rcv
The risetime of the channel is relatively slow compared to the very fast 1’st channel. i.e. modern channel’s risetime is quite longer than the UI, thus the eye blures and ‘ISI’-s itself.
2007/06/10 Confidential V1.16
High-Speed Serial Data Link Analysis The Serial Data’s Solution to a Closed Eye
An “Open Eye” at the Transmitter
a “Closed Eye” at the Receiver
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Rcv
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Equalize it!
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EQ.
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Rx
Equalization is the answer for the digital receiver. The eye opens at the input of the receiver, the receiver can decode the signal.
2007/06/10 Confidential V1.17
High-Speed Serial Data Link Analysis What should the Measurement do? - simple:do what your Tx/Rx does: implement equalization!
An “Open Eye” at the Transmitter
a “Closed Eye” at the Receiver
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Tx +
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Rcv
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Equalize it!
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EQ.
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Rx
Equalization is the answer to the eSerial receiver, so SW-implemented Equalization on the scope is also the answer to T&M.
-opens the eye for display (the scope-‘receiver’)
-Lets the user view ‘the inside’ of the Receiver This is now in your scope
Tektronix Confidential8
Tek Solution
DSA8200 with the TDR Module
80E04 reflected rise time: – 35 ps
80E10 reflected rise time– 12ps / 15ps
8 acquisition channels– 8-port TDR– 4-port True Differential TDR
Continuously stabilized rho and impedance waveforms
All standard measurements available on rho and impedance waveforms
TDR Overview - Typical System
Incident Step
50
Step Generator
Reflections
Sampler
t = 050
Incident Step
Incident
Reflection
Test deviceTest device
Probe
Impedance reference
TDR Waveform Characteristics
TDR systems observe the superposition of incident and reflected signals at source
Time separation t1-t0 assures ability to discern difference
Timet0 t1
incidentV
reflectedV
TDR Rho Units Definition
Time
+ 1
0
- 1
t0 t1
0at 0 and ZZV
V
incident
reflected
Characteristic (Z = Z0)
Amplitude
incidentV
reflectedV
KCL Applied at Discontinuity Transmission lines support propagation with specific
characteristic impedance Z
Reflected and forward propagating signals will be such that i = 0 is satisfied at discontinuity
Can easily solve for Z knowing , Z0, and KCL for lumped circuits
StepSource
Forward
(Z = Z0)
Incident
ReflectedDiscontinui
ty
Z0
Solution for Z Units
0
0
ZZ
ZZ
1
10ZZ
Where– Z0 is the known reference impedance– the sampling oscilloscopedirectly measures – Z is the calculated test device impedance
Note textbooks usually show reversed expression
TDR Waveforms - Simple Cases
Waveforms with Open, Short and 50 terminations
AmplitudeOpen (Z =)
(Z = 50)
Short (Z = 0)
Time
reflected =+1
+ 1
0
- 1
t0 t1
incident=+1 reflected =-1
Tektronix Confidential15
TDS Measurement Basics
TDR Block Diagram
Z termination
C ab le: Z 0, tdR source
TD
R O
scill
osc
op
e F
ron
t P
an
el
R source = 50 Z 0 = 50 then V inc ident = ½ V
V inc identV re flected
V
D U T: Z D U T
½ V
0
Z load > Z 0
Z load < Z 0
V •Z load / (Z load + Z 0)V
½ V
0
O pen c ircu it
Short c irc u it
M atched load
Tektronix Confidential16
TDR Measurements Basics
Inductance and Capacitance Analysis
L-C d isco ntinuity
C -L -C d iscontinuity
Z 0Z 0
Z 0Z 0
S hunt C d isco ntinuity
S eries L d isco ntinui ty
Z 0 Z 0
Z 0Z 0
½ V
0
½ V
0
½ V
0
½ V
0
Tektronix Confidential17
Measurement Tools: Z-line
Z-line-Based Measurements
2
12
1t
t
dttZL )( 2
1
1
2
1t
t
dttZ
C)(
t2
t1
t2
t1
Tektronix Confidential18
TDR Measurements Basics
TDR Rise Time and Resolution
Accepted rule of thumb for resolving two discontinuities
80E04 TDR rise time: 30-40ps at the end of the cable, probe, fixture– Base 1/2trise resolution: 15-20ps– 0.1”-0.12” in FR4
80E10 TDR rise time: 12-16ps at the end of the cable, probe, fixture– Base 1/2trise resolution: 6-8ps– 0.04”-0.048” in FR4
tseparateTo resolve a1 and a2 as
separate discontinuities:tseparate > tTDR_risetime /2 a1 a2
Tektronix Confidential19
TDR Measurements Basics
TDR Rise Time and Resolution
More real case: resolving a single discontinuity
Going beyond the TDR resolution and risetime: relative techniques– Signal integrity modeling – JEDEC standard– Failure analysis – golden device comparisons
tsingle a1 is not resolved iftsingle << tTDR_risetime a1
Tektronix Confidential20
TDR Measurements Basics
TDR Rise Time and Resolution
If 30-40 ps (or 12 ps) fast TDR rise time does not resolve it ….
How in the world a 80 ps signal rise time will????????????
Conclusion: for SI analysis, use the actual DUT rise time! (filter down the rise time, if necessary)
Tektronix Confidential21
TDR Measurements Basics
Differential TDR
Differential serial link analysis
Virtual ground plane
Even and odd mode measurements
C ab le: Z 0, tdR so urce
TD
R O
scill
osc
op
e F
ron
t Pa
ne
l
V inc ide ntV re flecte d
D U T: Z D U T
V
V
C ab le: Z 0, td
Virtual g round
R so urce
Tektronix Confidential22
TDR Measurements Basics
Good Measurement Practices
Perform calibration routines regularly
Minimum warm-up time 20 minutes
Maintain constant temperature in the lab and check the instrument t°
Zoom in on the DUT – but include all the DUT signature transitions (more to follow)
Use torque wrenches when mating SMA or other RF connectors
Tektronix Confidential23
Time and Frequency Domains
VNA Block Diagram
VNA: Vector Network Analyzer
Similar diagram can be drawn for reverse measurements (port 2 to port 1)
Differential VNA: 4-port measurements
DUTV incident1 V transmitted2
V reflected1
Port 1
Port 2
Cable: Z 0, tdV
NA
Fro
nt P
anel
R source
Calibrationprocedures:- SOLT- TRL- LRRM
V
Tektronix Confidential24
Time and Frequency Domains
Equations for TDR vs. VNA
))(()(11 tFFTLimitedDurationfS
0)(
0)(
1
111 ZZ
ZZ
V
VS
DUTinput
DUTinput
incident
reflected
11
110)( 1
1
S
SZZ DUTinput
0
0
ZZ
ZZ
V
V
load
load
incident
reflected
1
10ZZDUTTDR
VNA
))(()(21 tFFTLimitedDurationfS
Tektronix Confidential25
Time and Frequency Domains
TDR vs. VNA
TDNA (Time Domain Network Analysis)– Based on TDR/T measurements:– Transient– Broadband– More intuitive for a digital designer– Dynamic range: about 50-60dB– Less expensive
FDNA (Frequency Domain Network Analysis)– Based on VNA measurements:– Steady-state measurements– Narrow-band– More intuitive for microwave/RF designer– More expensive– Higher dynamic range (up to 110 dB)
Tektronix Confidential26
Time and Frequency Domains
Time or Frequency Domain?
SI measurements do not require high dynamic range
Compliance testing does not require high DR– About –10 dB for insertion loss– -25 to –35 dB for return loss– Higher for frequency domain crosstalk
VHIGH
VLOW
1% (-40dB) Xtalk
-40dB equals1% in time
domain
Tektronix Confidential27
Impedance Accuracy
TDR Basic Equations
V inc ident
0
V m easured =V inc ident + V reflec ted
2 td
measuredincident
measured
reflectedincident
reflectedincidentDUT VV
VZ
VV
VVZZZ
21
1000
0
0
ZZ
ZZVV
DUT
DUTincidentreflected
0
0
ZZ
ZZ
V
V
load
load
incident
reflected
Tektronix Confidential28
Impedance Accuracy
TDR Multiple Reflection Effects
Issue: impedance accuracy suffers due to signal re-reflection inside the DUT
Z0 Z1 Z2 Z3 Z4
Vtransmitted1
Vreflected1 Vreflected2
t0
Time Direction of propagation
Tektronix Confidential29
Impedance AccuracyIConnect Computation of the True Impedance Profile
nincident
incident
incident
incident
nnnnreflected
reflected
reflected
reflected
V
V
V
V
kkkk
kkk
kk
k
V
V
V
V
3
2
1
121
123
12
1
3
2
1
0
0
000
000
31222111
22
2132
22
213
2112212
111
)( incidentincidentincidentreflected
incidentincidentreflected
incidentreflected
VVtVtttV
VVtV
VV
Tektronix Confidential30
Impedance Accuracy
Board Trace IConnect® Z-line
Multiple reflections in TDR waveform
Scope reads here about 44 Ohm instead of 50 Ohm
Tektronix Confidential31
Impedance Accuracy
Board Trace IConnect® Z-line
Accurate impedanceprofile in IConnect®
Tektronix Confidential32
Impedance Accuracy
Package Trace IConnect® Z-line
Raw TDR: confusing multiple reflections
Impedance profile in IConnect®:Exact failure location,improved resolution
Tektronix Confidential33
Impedance Accuracy
IConnect® Software Z-line Algorithm
TDR measurements suffer from multiple reflections– No limited to TDR, also in TD in VNA
IConnect removes multiple reflections– Ensures accurate impedance measurements in multi-impedance
DUT– Direct and accurate readout of Z, td, L, C– Different and more accurate than Z readout in the scope
Attention!:– Data noise may interfere with accuracy
Use scope averaging Use software noise filtering
– Line loss is extracted separately
Tektronix Confidential34
Frequency Dependent S-parameters
Why S-parameters
Compliance testing– Insertion loss (around 6-10 dB)– Return loss (around 20-30 dB)– Frequency domain crosstalk
Link performance evaluation and simulation– Simulate S-parameters directly
Tektronix Confidential35
Frequency Dependent S-parameters Equations for TDR vs. VNA
0)(
0)(
1
111 ZZ
ZZ
V
VS
DUTinput
DUTinput
incident
reflected
11
110)( 1
1
S
SZZ DUTinput
0
0
ZZ
ZZ
V
V
load
load
incident
reflected
1
10ZZDUTTDR
VNA
))(()(11 tFFTLimitedDurationfS
))(()(21 tFFTLimitedDurationfS
Tektronix Confidential36
Frequency Dependent S-parameters
Single-ended TDR
22222121
12121111
TDRSTDTS
TDTSTDRS
TDR stimulus on channel 2,response on channel 2
TDR stimulus on channel 2,response on channel 1
TDR stimulus on channel 1,response on channel 1
TDR stimulus on channel 1,response on channel 2
Tektronix Confidential37
Frequency Dependent S-parameters
Correct Data Acquisition
DUT waveform to settle to steady DC
level
Tektronix Confidential38
Frequency Dependent S-parameters
Return Loss = TDR
Measure TDR, compute S11 (return loss) in IConnect
What is wrong with this RL picture?
Tektronix Confidential39
Frequency Dependent S-parameters
Insertion Loss = TDT
Measure TDT, compute S21 (insertion loss) in IConnect
Test casefor loss extraction
Tektronix Confidential40
Frequency Dependent S-parameters
Differential and Mixed S-parameters
2222212122222121
1212111112121111
2222212122222121
1212111112121111
cccccccccdcdcdcd
cccccccccdcdcdcd
dcdcdcdcdddddddd
dcdcdcdcdddddddd
TDRSTDTSTDTSTDTS
TDTSTDRSTDTSTDRS
TDRSTDRSTDRSTDTS
TDTSTDRSTDTSTDRS
Differential TDR stimulus,differential response
(most important)
Common mode TDR stimulus,common mode response
(less important)
Differential TDR stimulus,common mode response(useful in time domain for
EMI troubleshooting)
Common mode TDR stimulus,differential response
(useful in time domain for EMItroubleshooting)
Tektronix Confidential41
Frequency Dependent S-parameters
Differential TDR = S11diff
Several InfiniBand traces of different length.
Differential return loss.
Demo of TDR and S parameter measurements
Tektronix Confidential42
Additional Material
Tektronix Confidential43
Tektronix Confidential44
Tektronix Confidential45
Frequency Dependent S-parameters
Power Plane Resonance
Resonances between planes
Observe plane impedance profile (Z-line)
Tektronix Confidential46
Frequency Dependent S-parameters
Electrical Compliance Testing
Need fixture to interface to interconnects for compliance testing
Infiniband Connector
Reference thru Traces
DUT Connection Traces
Tektronix Confidential47
Frequency Dependent S-parameters
VNA Fixture De-embedding
For VNA requires additional standard to de-embed properly
Insertion loss: fixture insertion loss must be subtracted from DUT insertion loss
Return loss: no way to de-embed without additional standards!– Fixture return loss ends up being lumped with the DUT return
loss– Can be a problem even with quality fixtures
Tektronix Confidential48
Frequency Dependent S-parameters
VNA Real Fixture Limitation Example
With fixture, the cable assembly is failing the
spec!Fixture is failing the assembly with VNA
measurements
Spec: -10 dB at 1.25 GHz
Tektronix Confidential49
Frequency Dependent S-parameters
TD-VNA Fixture De-embedding
Simplicity of calibration allows simple fixture de-embedding
Fixture de-embedded with TDNA, the assembly is passing
Spec: -10 dB at 1.25 GHz
Tektronix Confidential50
Frequency Dependent S-parameters
Correlation with Network Analyzer
Tektronix Confidential51
Frequency Dependent S-parameters
Correlation with Network Analyzer
-25
-20
-15
-10
-5
0
FR
EQ
, Gh
z
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
VNA SDD11, dB
IConnect®S11.wfm(dBMag). NoTDR calibration
Tektronix Confidential52
Frequency Dependent S-parameters
Correlation with Network Analyzer
Insertion Loss VNA TDA ComparisonData courtesy Kieran Kelly, Samtec,Inc.
-12
-10
-8
-6
-4
-2
0
000.0E+0
1.0E+9 2.0E+9 3.0E+9 4.0E+9 5.0E+9 6.0E+9 7.0E+9 8.0E+9 9.0E+9 10.0E+9
Frequency (Hz)
IL (
dB
)
VNA
TDA
Tektronix Confidential53
Frequency Dependent S-parameters
Correlation with Network Analyzer: 65 GHz
The TD-VNA bandwidth is directly related to TDR/T rise time
These data were measured using the PSPL Model 4022 and a 70 GHz sampler
S-parameters correlate to65 GHz
Courtesy: Kipp Schoen, Picosecond Pulse Labs
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
0 10 20 30 40 50 60
frequency (GHz)
S2
1 m
ag
na
tud
e (
dB
)
VNA S21
4022 S21
-60
-50
-40
-30
-20
-10
0
0 10 20 30 40 50 60
frequency (GHz)
S1
1 m
ag
na
tud
e (
dB
)VNA
4022
Tektronix Confidential54
Frequency Dependent S-parameters
Calibrated Results: SOLT
Excellent correlation between TDNA and FDNA data
Dashed line – Tektronix 11801 with SOLT cal
Solid line – Agilent 8510 VNA
Tektronix Confidential55
Frequency Dependent S-parameters
Noise Floor and Dynamic Range
To reduce noise floor:– Increase number of averages Navg– Increase number of points Npoints– Decrease acquisition window length (increase effective incident
power)
Tektronix Confidential56
Frequency Dependent S-parameters
TD-VNA Incident Effective Power
The TD-VNA bandwidth directly related to the risetime of the TDR and TDT signals
-140
-120
-100
-80
-60
-40
-20
0
0 20 40 60 80 100
frequency (GHz)
ma
gn
atu
de
(d
B)
4022 10ps
54754A 25ps
4022 10 ps TDR 25 ps
Tektronix Confidential57
Frequency Dependent S-parametersTD-VNA Dynamic Range (with PSPL Module)
Tektronix Confidential58
Frequency Dependent S-parameters
IConnect Produces S-parameters
Differential, mixed mode and single ended
Insertion, return loss and frequency domain crosstalk
Performance with base DSA8200: 50-60 dB dynamic range (vs. 100 dB for VNA), 12 GHz bandwidth
Performance with 80E10 up to 50GHz bandwidth
Cost ½ of a comparable VNA solution
Intuitive, easy to use and more than adequate dynamic range for digital designers
Tektronix Confidential59
TDT and IConnect Eye Diagram
Efficient S-parameters Testing in IConnect
Easy, quick, efficient S-parameter measurements and electrical compliance testing– Insertion, return loss, frequency dependent crosstalk– Excellent correlation with traditional VNA techniques– Cost-effective and quick
Minimal calibration required– Only reference at the end of the fixture– Easy fixture de-embedding
Tektronix Confidential60
TDT and IConnect Eye Diagram
Why Eye Diagram in IConnect?
Eye Diagram for Interconnects– Specification mask testing– Not just communication standards, also for new serial link
standards
IConnect benefit: no pattern generator required for interconnect eye diagram analysis– De-embed deterministic / interconnect jitter– No active component jitter
Tektronix Confidential61
TDT and IConnect Eye Diagram
Eye Diagram Degradation in Interconnects
Interconnect losses
Pattern-dependent, crosstalk induced jitter
Method to improve the eye– Equalization, pre-emphasis and de-emphasis– Other signal conditioning techniques
Only deterministic jitter exists in interconnects, no random component!
Tektronix Confidential62
TDT and IConnect Eye Diagram
Eye Diagram Options
TDT easily gives the eye diagram degradation– Deterministic jitter only
Tektronix Confidential63
TDT and IConnect Eye Diagram
New Eye Mask and Jitter Measurements
Tektronix Confidential64
TDT and IConnect Eye Diagram
Why is TDT Based Eye Better?
Easy to de-embed fixture– The same improvement as for S-parameter
measurements!
No jitter from the pattern generator
Tektronix Confidential65
TDT and IConnect Eye Diagram
Predicted and Measured Eye Diagrams
Pattern Generator Based
IConnect K28.5
IConnectPRBS 210-1
Tektronix Confidential66
TDT and IConnect Eye Diagram
Predicted and Measured Eye Diagrams
2^10-1 IConnect eye fromTDT measurement
2^10-1 pattern generator measurement
Data Courtesy FCI Electronics
Tektronix Confidential67
TDT and IConnect Eye Diagram
Predicted and Measured Eye Diagrams
MeasuredSimulated
MeasuredSimulated
1.5Gb/s (Gen 1)
6.0Gb/s (Gen 3)
MeasuredSimulated
3.0Gb/s (Gen 2)
Serial ATA data courtesy Molex, Inc.
Tektronix Confidential68
TDT and IConnect Eye Diagram
Efficient Eye Diagram Testing in IConnect
Easy, quick, efficient eye diagram measurements and compliance testing– Excellent correlation with traditional pattern generator
techniques– Cost-effective and quick
Minimal calibration required– Only reference at the end of the fixture– Easy fixture de-embedding
Tektronix Confidential69
Outline
Interconnect Measurement Accuracy Issues TDR/T Probing and Fixturing
App Note: “TDR Measurement Primer”App Note: “TDR Techniques for Characterization and Modeling of Electronic Packaging”Quick Guide:“Interconnect Probing Quick Guide”
Interconnect SPICE / IBIS Modeling and Model Validation
Tektronix Confidential70
Probing and Fixturing
TDR Measurement Setup
TDR probe with signal and ground
connection
TDR oscilloscope
Tektronix Confidential71
Probing and Fixturing
Probing and Fixturing Issues
Probing is the weakest link!
Start with a probe– 50 Ohm for TDR measurements – must be rugged and inexpensive– ensure stable repeatable contact– large pitch* means small bandwidth– variable pitch means poor repeatability– ensure sufficient compliance
* Pitch: center-to-center signal to ground pad spacing
Tektronix Confidential72
Probing and Fixturing
Package and Connector Probing
Use a high-quality probe (and positioner) Need an interface adapter or fixture to probe Fixturing requirements
– Reproduce the real application environment– Ensure easy fixture de-embedding (reference short and open
structures may be needed)
P ackage
S igna l-G roundP robe
V ias topackage
leads
P C B providesground
connections
F ixtu regroundp lane
P C B provides groundconnections
P C B trace toconnector lead
F ixtu regroundp lane
Via to ground for reference m easurem ents
R eferenceshort and open
S igna l-G roundP robe
H igh-S peed
C onnector
Tektronix Confidential73
Probing and Fixturing
Board Probing
Ensure good contact to a via – Difficult for a microwave probe– Use TDA’s QuickTDR™ probe– Probes also available from TDR
manufacturers
Ensure ground contacts near yoursignals
Variable pitch: a sad necessity– Available from from TDR manufacturers and probe
manufacturers (Cascade Microtech, ICM)– Measurements suffer from poor repeatability and decrease the
instrument usable bandwidth
Tektronix Confidential74
Probing and Fixturing
Probing vs. Fixturing
Probing advantages: Maximum flexibility for multiple
device measurements
No fixture de-embedding required
But:
Requires DUT to have easily accessible contact areas
Positioning system may be expensive
Fixturing advantages: Evaluate the DUT in its
intended environment of use (example: package on a board)
Great flexibility for specific DUT
But: Difficult to change after the
fixture has been designed Must de-embed fixturing from
measurements
These approaches are complementary!
Fixturing is thinking ahead about how you will probe!
Tektronix Confidential75
Outline
Interconnect Measurement Accuracy Issues– Impedance, S-parameters and eye diagram measurements and
compliance testing
Interconnect SPICE / IBIS Modeling and Model Validation– Z-line, lossy line, and automatic behavioral modeling
Tektronix Confidential76
Outline
Interconnect Measurement Accuracy Issues
Interconnect SPICE / IBIS Modeling and Model Validation Measurement Based Interconnect Analysis– Behavioral Modeling: MeasureXtractor™ – Topological Modeling:
TDT and Lossy Line Modeling Impedance Profile (Z-line) Transmission Line Modeling L and C JEDEC computation
– Examples: Power Plane Analysis Backplanes and cable assemblies
Tektronix Confidential77
Measurement-Based Link Design
How to Analyze System Signal Integrity?
App Note: “Signal Integrity Modeling of Gigabit Backplanes, Cables and Connectors Using TDR”
Is this similar to your application?
Tx
Daughtercard
Backplane
CableAssem bly
Board C onnector(s im plified
m odel)
Rx
Connector
Connector
Connector
Tektronix Confidential78
Measurement-Based Link Design
Interconnect Measurement Based Design
Linearize the link input and termination for initial analysis
Daughtercard
Backplane
CableAssem bly
Board C onnector(s im plified
m odel)
Connector
Connector
Connector
Receiversim plified
Tektronix Confidential79
Measurement-Based Link Design
Measurement Based Design Details
Impedance measurement => reflections
TDR/T or S-parameters => losses, jitter, eye diagram degradation– System losses is a result of losses in components– Eye diagram is a result of losses and crosstalk in
components
Tektronix Confidential80
IConnect Modeling Methodology
Goals and Model Validity
Goal: accurately predict interconnect performance via simulations– Need an accurate SPICE /IBIS models
Model required range of validity is defined by the fast corner rise time of the driver– Equivalent bandwidth estimated as:
fbw=0.35 / trise or harmonics of clock
It may be desired to extend the required range of model validity beyond trise and fbw
– Have a confidence guard band
Tektronix Confidential81
IConnect Modeling Methodology
Modeling Technique: Behavioral
Behavioral Modeling: MeasureXtractor™– A universal, fully automatic, exact
modeling technique– Can use time or frequency domain data – Matches exactly both time and frequency response– Perfect for…
Connector, package or socket modeling Model for a characterization fixture for a connector, a package or a
cable Model for a daughtercard board When behavioral model is acceptable
– Can create large model for a large interconnect such as a backplane or cable assembly
Tektronix Confidential82
IConnect Modeling Methodology
Modeling Technique: Topological
Lossy line and coupled lossy line modeling– When need to predict losses and crosstalk
Large lossy backplanes and motherboards Cables and cable assemblies
Impedance profile (Z-line) models– When losses are small– Need to predict impedance reflections, crosstalk only
Small daughtercards, boards Electrically long connectors, packages
Tektronix Confidential83
IConnect Modeling Methodology
Modeling Technique: Topological
JEDEC technique for L and C computation– Industry standard technique for electrically short interconnects– Electrically short: trise >> tprop delay
– Packages, connectors, sockets
trise
tprop delay
Tektronix Confidential84
IConnect Modeling Methodology
Behavioral or Topological?
Behavioral Topological Measurement Requirements
Requires two-port or four-port measurements
Just TDR (reflection) is sufficient
Topology selection
Automatic, no user intervention
User-controlled (easy and intuitive from TDR measurements)
Extraction Automatic, no user intervention
User-driven; more labor intensive than behavioral
Type of models
“Black-box,” no internal changes allowed
Intuitive, easy “what-if” scenario analysis
Limitation for long interconnects
Large model for long interconnects (backplanes, cable assemblies)
Efficient model extraction processes exist for large interconnects
Tektronix Confidential85
IConnect Modeling Methodology
Methodology: Gbit Ethernet Example
Cable and Test cards: lossy line modeling
Launch, high-speed connector:Z-line modeling
Any piece can be modeled in MeasureXtractor™
Lumped pieces can be modeledwith JEDEC technique
Tektronix Confidential86
TDR/T or VNA Measurements
Extracted interconnect, instrument source models
Direct link to simulators
Automatic comparison of simulation and measurement in IConnect waveform viewer
SPICE
IConnect Modeling Methodology
Measurement Based Approach
Tektronix Confidential87
Outline
Interconnect Measurement Accuracy Issues
Interconnect SPICE / IBIS Modeling and Model Validation Behavioral Modeling: MeasureXtractor™ – Topological Modeling:
TDT and Lossy Line Modeling Impedance Profile (Z-line) Transmission Line Modeling L and C JEDEC computation
– Examples: Power Plane Analysis Backplanes and cable assemblies
Tektronix Confidential88
Behavioral Modeling
MeasureXtractor™ Modeling
A fully automatic algorithm for conversion of VNA S-parameter or TDR/T data into SPICE or IBIS model– Passivity of the model guaranteed– Compact and efficient– Fully automated– Not an optimization– Behavioral models
Tektronix Confidential89
Behavioral Modeling
Lack of Passivity Produces Oscillations
Instability is a very bad
thing!
TERASPEEDCONSULTING
GROUP
Slide
courtesy:
Tektronix Confidential90
Behavioral Modeling
Sources of Passivity Issues
Insufficient attention to measurements or calibration– Interconnects do not amplify signals!– Even if individual measurements are passive, combined system
measurements can have amplification properties
Simulator extrapolation and interpolation based on model, not original measurement
Finite measurement acquisition window (in the limit, the data is infinite!)
Tektronix Confidential91
Behavioral ModelingExample: Correlation of Measurement and Model
Exact correlation in time and frequency domains
Tektronix Confidential92
Behavioral Modeling
Example: Model Listing
c33 34 gnd_ 7.10021e-016
r90 35 gnd_ 3622.1
c34 35 gnd_ -7.10021e-016
r91 36 37 176812
r92 36 gnd_ 57641.7
c35 36 gnd_ 7.15572e-016
r93 37 gnd_ 3932.13
c36 37 gnd_ -7.15572e-016
r94 38 gnd_ -2488.86
c37 38 gnd_ -3.07009e-015
r95 39 gnd_ 5982.67
c38 39 gnd_ -2.49077e-014
.ends
…
…
…
…
r14 port1 15 -1898.27
r15 port1 16 -971048
r16 port1 17 2103.52
r17 port1 18 15884.8
r18 port1 19 326913
r19 port1 20 6566.94
r20 port1 21 1508.55
r21 port1 22 -885.906
r22 port1 23 4789.5
r23 port1 24 2788.21
r24 port1 25 -14075.7
r25 port1 26 -18495.7
r26 port1 27 -1786.85
r27 port1 28 -27328.6
…
.subckt DUT port1 gnd_
r1 port1 2 -24977.9
r2 port1 3 23982.9
r3 port1 4 -12111
r4 port1 5 3124.2
r5 port1 6 -2348.66
r6 port1 7 14099.3
r7 port1 8 -4392.43
r8 port1 9 1444.76
r9 port1 10 1.1046e+007
r10 port1 11 -301858
r11 port1 12 3622.64
r12 port1 13 -1221.14
r13 port1 14 6965.14
…
Tektronix Confidential93
Behavioral Modeling
MeasureXtractor™ Summary
Converts S-parameters or TDR/T data into an exact-match model
Passivity is guaranteed
If you can measure it, and want model it with little effort, use MeasureXtractor™!
Tektronix Confidential94
Outline
Interconnect Measurement Accuracy Issues
Interconnect SPICE / IBIS Modeling and Model Validation Topological Modeling:
TDT and Lossy Line ModelingApp Note: “Practical Characterization of Lossy Transmission Lines Using TDR”
Impedance Profile (Z-line) Transmission Line Modeling L and C JEDEC computation
– Examples: Power Plane Analysis Backplanes and cable assemblies
Tektronix Confidential95
TDT and IConnect Lossy Lines
TDT and Lossy Line Modeling Is For:
Long lossy transmission lines in backplanes and motherboards
Long lossy cables
Tektronix Confidential96
TDT and IConnect Lossy LinesLoss Example: Time and Frequency Domain
Tektronix Confidential97
TDT and IConnect Lossy Lines
Skin Effect vs. Dielectric Loss
Typical FR-4 50 Ohm Trace
Tektronix Confidential98
TDT and IConnect Lossy Lines
Different Loss Modeling Approaches
Lumped (behavioral)– Defined for all frequencies– Slow for long lines
Distributed– Based on parameters (Rskin, Gdielectric)
Defined for all frequencies Not as general
– Based on RLGC data General for quasi-TEM Not defined for all frequencies
Tektronix Confidential99
TDT and IConnect Lossy Lines
Causality in TEM Models
From basic physics, the real and imaginary parts of the dielectric constant are tightly related to ensure causality.
The same is true of the permeability constant, In TEM modeling, this means that R and L are related,
and G and C are related
Models based on RLGC data (or S-parameters) should
address this issue !!!
Tektronix Confidential100
TDT and IConnect Lossy Lines
Our Model Extraction Approach
Assume standard simulator equations:
Two extraction methods:– Open circuit reflection (TDR, one port)– Matched circuit transmission (TDR, TDT, two-port)
Extract loss parameters: Rdc, Rac, Gdc, Gac, L, C Write resulting model in various formats
– Lumped– Distributed with parameters– Distributed with RLGC data
CjfGGY
LjfRRZ
acdc
acdc
Tektronix Confidential101
TDT and IConnect Lossy LinesExample: Extraction Results (Transmission)
Extracted skin effect and dielectric loss parameters
Simulated and measured transmission
Tektronix Confidential102
TDT and IConnect Lossy Lines
Symmetrical Lossy Coupled Line Model
Assumptions:– The lines are symmetrical– TDR steps are symmetrical– TDR steps arrive at the lines at the same time at the beginning
of both lines
B oard lines
TDR source 1
TDR source 2
Tektronix Confidential103
IConnect Differential TDR Techniques
Even/Odd vs. Common/Differential
mtot
mselfodd CC
LLZ
mtotmselfodd CCLLlt
mtot
mselfeven CC
LLZ
mtotmselfeven CCLLlt
oddaldifferenti ZZ 2
oddaldifferenti tt
2even
commonZZ
evencommon tt
Tektronix Confidential104
IConnect Differential TDR Techniques
Even and Odd Impedance Profile Example
Note: - Odd mode = differential measurement (two TDR sources of opposite polarity) - Even mode = common mode measurement (two TDR sources of the same polarity)
Zeven>Zself>Zodd
teven>tself>todd
Tektronix Confidential105
TDT and IConnect Lossy LinesExample: Extraction Results (Reflection, Coupled)
Both self and mutual parameters are extracted
Tektronix Confidential106
Outline
Interconnect Measurement Accuracy Issues
Interconnect SPICE / IBIS Modeling and Model Validation Topological Modeling:
Impedance Profile (Z-line) Transmission Line ModelingApp Note: “PCB Interconnect Characterization from TDR Measurements” App Note: “Characterization of Differential Interconnect from TDR Measurements”
L and C JEDEC computation– Examples:
Power Plane Analysis Backplanes and cable assemblies
Tektronix Confidential107
IConnect Single-ended TDR Techniques
Single Transmission Line Modeling Is For:
Short (lossless) transmission lines
Electrically long packages (longer than Trise)
Electrically long connectors (longer than Trise)
Tektronix Confidential108
IConnect Single-ended TDR Techniques
Transmission Line Z and td
Directly available from impedance profile
Eliminate confusion about:– Exact impedance value– Exact electrical length of the lines
Z01
Z02
td
Tektronix Confidential109
IConnect Single-ended TDR Techniques
Via L and C
2
12
1t
t
dttZL )( 2
1
1
2
1t
t
dttZ
C)(
t2
t1
t2
t1
Tektronix Confidential110
IConnect Single-ended TDR Techniques
IConnect® Modeling Process
Measure and acquire
Process data
Extract model
Simulate, compare and verify
Tektronix Confidential111
IConnect Single-ended TDR Techniques
Modeling in IConnect Software
* Name: Automatically Generated
.subckt Single port1 port2 gnd_
****** Partition #1
c1 port1 gnd_ 456f
l1 port1 1 1.05n
****** Partition #2
t1 1 gnd_ 2 gnd_ Z0=50.8 TD=125p
…………..
****** Partition #4
t3 3 gnd_ port2 gnd_ Z0=48.2 TD=190p
.ends
Tektronix Confidential112
IConnect Single-ended TDR Techniques
Prepare to Simulate and Validate
Tektronix Confidential113
IConnect Single-ended TDR Techniques
Simulation and Validation Results
Tektronix Confidential114
IConnect Single-ended TDR TechniquesUsing Rise Time Filtering to Achieve Simple Models
Tektronix Confidential115
IConnect Differential TDR Techniques
Coupled Transmission Line Modeling Is For:
Differential transmission lines
Differential connectors and packages that are electrically long (longer than Trise)
Crosstalk prediction (differential and single ended, forward, backward)
Crosstalk induced jitter prediction
Tektronix Confidential116
IConnect Differential TDR Techniques
Differential Line Modeling
Short interconnect– Use lumped-coupled model
Long interconnect– Split lines in multiple segments
Longer yet interconnect– Symmetric distributed coupled line model– For longer lines, use lossy approach instead
-Z odd/2, todd
Z ev en/2, tev en
Z odd, todd
Z odd, todd
Tektronix Confidential117
IConnect Differential TDR Techniques
IConnect Differential Line Modeling
Tektronix Confidential118
IConnect Differential TDR Techniques
Composite Model Generation
* Name: Automatically Generated.subckt Symmetric 1 2 3 4 5****** Partition #1 t1 1 5 6 5 Z0=49.7 TD=92.3p t2 3 5 7 5 Z0=49.7 TD=92.3p****** Partition #2 l1 6 8 19n c1 8 5 6.44p l2 7 9 19n c2 9 5 6.44p c3 8 9 716f k1 l1 l2 207m .ends
Tektronix Confidential119
IConnect Differential TDR Techniques
Model Validation in IConnect
Tektronix Confidential120
IConnect Differential TDR Techniques
Coupled LC Computation in IConnect
Tektronix Confidential121
Outline
Interconnect Measurement Accuracy Issues
Interconnect SPICE / IBIS Modeling and Model Validation Topological Modeling:
L and C JEDEC computationApp Note: “TDR Techniques for Characterization and Modeling of Electronic Packaging”
– Examples: Power Plane Analysis Backplanes and cable assemblies
Tektronix Confidential122
IConnect Short Interconnect Modeling
When is Interconnect Lumped?
Practical rule of “short” or “lumped” (RLC) interconnect
trise
tprop delay
trise > tprop delay• (2 or 3)
Tektronix Confidential123
IConnect Short Interconnect Modeling
Short Interconnect Modeling is Used For:
IC packages
Connectors
Sockets
Vias on the board
Use only when short compared to Trise !!!
Tektronix Confidential124
IConnect Short Interconnect Modeling
Single Parasitic Inductance
dtVVV
ZdttZL
t
shortrefTDR
t
t
1
2
1
0
2
1)(
C ab le: Z 0, tdR source
TD
R O
scill
osc
op
e F
ron
t P
an
el V inc ident
V re flectedV
L
V T D R
V ref s hor tL
Tektronix Confidential125
IConnect Short Interconnect ModelingSingle-Ended TDR: Package Lead Inductance L Measurements
TDR waveform:– TDR into package lead.
Short all the leads to ground on the inside of the package.
Short the leads that are not being measured to ground on the outside of the package.
Short waveform:– TDR into the “short”; connect the
probe signal contact to ground on a conductive (metal) pad
Induced waveform: Measure near end crosstalk with far
end of the victim shorted
Background waveform: Corrects for the noise and scope DC
offset
V background noise
V induced
Lm utual
P ackageunder testTD R in to the
package lead
M easure re flection
M easure near-endcrossta lk in ad jacent
lead
Packa
ge le
ads
S hort leadends toground
0
0
2dtWW
V
ZL shortTDRself )(
0
0
2dtWW
V
ZL backgroundinducedmutual )(
W TDR
W shortL
Tektronix Confidential126
dtVVVZ
dttZ
Ct
TDRopenref
t
t
1
2
1 0
11
2
1
)(
C ab le: Z 0, tdR source
TD
R O
scill
osc
op
e F
ron
t P
an
el V inc ident
V re flectedV C
Open
V T D R
V ref open
C
IConnect Short Interconnect Modeling
Single Parasitic Capacitance
Tektronix Confidential127
IConnect Short Interconnect ModelingSingle-Ended TDR: Package Lead Capacitance C Measurements
TDR waveform:– TDR into package lead
Short the leads that are not being measured to ground on the outside of the package
Open waveform:– TDR into the “open”;disconnect the
probe from the DUT or remove the DUT from the fixture
Induced waveform:– Measure near end crosstalk with far
end of the victim open-ended
Background waveform:– Corrects for the noise and scope DC
offset
W TDR
W open
C
002
1dtWW
VZC TDRopenself )(
V background noise
V induced
Cm utual
002
1dtWW
VZC backgroundinducedmutual )(
P ackageunder testTD R in to the
package lead
M easure re flection
M easure near-endcrossta lk in ad jacent
lead
Packa
ge le
ads
K eep leadends open
Tektronix Confidential128
IConnect Short Interconnect Modeling
Input Die Capacitance Measurement
Tektronix Confidential129
IConnect Short Interconnect Modeling
Even-Odd Mode L and C Measurements
Compute C and L in even and odd mode
2
oddevenmutual
evenself
CCC
CC
2
2
oddevenmutual
oddevenself
LLL
LLL
TD R in to the two ad jacentsocket lead w ith d iffe rentia l and
com m on m ode stim ulus
M easure odd m ode TD R w ithd iffe rentia l stim ulus, and
even m ode TD R w ith com m onm ode stim ulus
P ackageunder test
Packa
ge le
ads
Tektronix Confidential130
IConnect Short Interconnect Modeling
Even-Odd Mode Impedance Profile
Compute C and L from even and odd Z-line
TD R in to the two ad jacentsocket lead w ith d iffe rentia l and
com m on m ode stim ulus
M easure odd m ode TD R w ithd iffe rentia l stim ulus, and
even m ode TD R w ith com m onm ode stim ulus
P ackageunder test
Packa
ge le
ads
oddoddevenevenself tZtZL 2
1
oddoddevenevenm tZtZL 2
1
even
even
odd
oddtot Z
t
Z
tC
2
1
even
even
odd
oddm Z
t
Z
tC
2
1
Ctotal = Cself + Cm
Tektronix Confidential131
Outline
Interconnect Measurement Accuracy Issues
Interconnect SPICE / IBIS Modeling and Model Validation Examples:
Power Plane Analysis Backplanes and cable assemblies
Tektronix Confidential132
Power Plane AnalysisPower Distribution Network (PDN) Test Vehicle
3"
1 3
/8" (3
5m
m)
Top plane
Via connection to bottom plane
P robe p lacem ent a t po in to f power app lica tion
P oin t o f power de livery
Pad connection to top plane
R eference short connection forinductance m easurem ent
Tektronix Confidential133
Power Plane Analysis
PDN Equivalent Models
R C
R C LR C 1 L
R
C
L
C 2
Tektronix Confidential134
Power Plane Analysis
PDN Capacitance Measurements
Tektronix Confidential135
Power Plane Analysis
PDN Impedance
Tektronix Confidential136
Power Plane Analysis
PDN Resonance: Analysis for Bypass Caps
Tektronix Confidential137
Power Plane Analysis
PDN Model Validation
Tektronix Confidential138
Power Plane Analysis
PDN Model Accuracy
Tektronix Confidential139
Power Plane Via
Power Via Inductance
22oddeven
mutualoddeven
self
LLL
LLL
oddoddevenevenmutualoddoddevenevenself tZtZLtZtZL 2
1
2
1
Tektronix Confidential140
Power Plane Via
Example: Via Modeling
***** Partition #1 l1 port1 1 1.9n l2 port3 2 1.9n k1 l1 l2 200m
Correlation between simulation and measurement
Tektronix Confidential141
Outline
Interconnect Measurement Accuracy Issues
Interconnect SPICE / IBIS Modeling and Model Validation Examples:
Backplanes and cable assemblies
Tektronix Confidential142
Putting It All TogetherComplete Topological Modeling Methodology
Connectors, packages:– Short structures => use lumped elements (LC) or lossless T-
lines – Use the true impedance profile approach
Cables – lossy transmission line
Backplane traces – lossy transmission line
Combine the model and verify the accuracy with simulations
Note that MeasureXtractor™ can do any of that! (behaviorally)
Tektronix Confidential143
Single-ended Example
Example: IConnect-Extracted Model
LCL=700pHC=280fF
T-lineZ=53 OhmTd=520ps(short => lossless)
CLCL=6nHC=1.5pF
W-lineL=198nH, C=69.7pFRo=0.18 OhmRs=0.2uOhmGd=6.7nS (nMho)(long => lossy)
Tektronix Confidential144
Single-ended Example
Simulation Results
Tektronix Confidential145
Differential Example
Backplane Example
Courtesy FCI Electronics
Tektronix Confidential146
Differential Example
Backplane Example: PCI-X Eye Diagram
Tektronix Confidential147
Differential Example
Backplane Example
Differential measurement, full mode analysis
Daughter Card Backplane Daughter Card
Connector Connector
Tektronix Confidential148
Differential Example
Daughter Card and Backplane Models
Daughter Card Model (odd mode)
Backplane Model (odd mode)
Tektronix Confidential149
Differential Example
Full Daughter Card Modeling
Tektronix Confidential150
Differential Example
Full Backplane Modeling
Tektronix Confidential151
Differential Example
Simulation Results
Tektronix Confidential152
Differential Example
Jitter De-Embedding: Daughter Card Only
Tektronix Confidential153
Differential Example
Jitter De-Embedding: Backplane Only
Tektronix Confidential154
Outline
Interconnect Measurement Accuracy Issues– Impedance, S-parameters and eye diagram measurements
Interconnect SPICE / IBIS Modeling and Model Validation– Z-line, lossy line, and automatic behavioral modeling
Tektronix Confidential155
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