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![Page 1: The Interconnect Modeling Company™ High-Speed Interconnect Measurements and Modeling Dima Smolyansky TDA Systems, Inc. dima@tdasystems.com.](https://reader031.fdocuments.net/reader031/viewer/2022031921/56649f585503460f94c7d9e1/html5/thumbnails/1.jpg)
The Interconnect Modeling Company™
High-Speed Interconnect Measurements and Modeling
Dima SmolyanskyTDA Systems, Inc.
![Page 2: The Interconnect Modeling Company™ High-Speed Interconnect Measurements and Modeling Dima Smolyansky TDA Systems, Inc. dima@tdasystems.com.](https://reader031.fdocuments.net/reader031/viewer/2022031921/56649f585503460f94c7d9e1/html5/thumbnails/2.jpg)
The Interconnect Modeling Company™
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
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The Interconnect Modeling Company™
Signal Integrity Issues
Propagation delay Reflections Crosstalk
SPICE/IBIS simulations and accurate interconnect models are required
Loss Ground bounce Dispersion
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The Interconnect Modeling Company™
TDR Measurements
Transient measurements Windowing capability Very useful for signal integrity work Can model complex structures
– but – multiple reflections impede accuracy
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The Interconnect Modeling Company™
Tektronix TDS/CSA8000
TDR rise time:
– 35 ps reflected
– < 30ps typical 8 acquisition channels
– 8-port TDR
– 4-port differential TDR Impedance and crosstalk
characterization High resolution and
measurement repeatability Windows interface
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The Interconnect Modeling Company™
TDR Block Diagram
Z termination
Cable: Z 0, tdR source
TD
R O
scill
osco
pe F
ront
P
anel
R source = 50 Z 0 = 50 then V incident = ½V
V incidentV reflected
V
DUT: Z D UT
Note: in reality, TDR source is a current source (Norton equivalent)
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The Interconnect Modeling Company™
TDR Visual Representation
½ V
0
Z load > Z 0
Z load < Z 0
V •Z load / (Z load + Z 0)V
½ V
0
Open circuit
Short circuit
Matched load
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The Interconnect Modeling Company™
Inductance and Capacitance Analysis
L-C discontinuity
C-L-C discontinuity
Z 0Z 0
Z 0Z 0
Shunt C discontinuity
Series L discontinuity
Z 0 Z 0
Z 0Z 0
½ V
0
½ V
0
½ V
0
½ V
0
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The Interconnect Modeling Company™
TDR Multiple Reflection Effects
Z0 Z1 Z2 Z3 Z4
Vtransmitted1
Vreflected1 Vreflected2
t0
Time Direction of propagation
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The Interconnect Modeling Company™
Z-line Example
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The Interconnect Modeling Company™
Signal Integrity Modeling
Goal: create SPICE models to predict connector/cable performance
Model required range of validity is defined by a greater of
– signal rise time: fbw=0.35 / trise
– signal clock rate: fbw= (3~5) ·fclock
It may be desired to extend the required range of model validity beyond fbw
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The Interconnect Modeling Company™
Measurement Based Approach
M easure
M odel
S im ulate
Com pare and Verify
Com ponent S im ulations
Com ponent SP ICE M odel
Com pare and Verify M odel
System Layout
Com ponentM easurem ents
Fin
e-T
un
e t
he
Mo
de
l
System S im ulations
IC onnect™ approach:S tart from existing off-the-shelf com ponent
Co
mp
on
en
t R
ed
esig
n
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The Interconnect Modeling Company™
Measurement Role in Analytical Approach
Component Simulations
Compare and Verify Model
System Layout
ComponentMeasurementsF
ine
-Tu
ne
th
e M
od
el
System Simulations
IConnect™ approach:Start from existing model
EM Field SolverModels
Component Prototype
Component SPICE Model
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The Interconnect Modeling Company™
Partitioning Impedance Profile Waveform
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The Interconnect Modeling Company™
Composite Model Generation
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The Interconnect Modeling Company™
Model Simulation and Verification
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The Interconnect Modeling Company™
Using Rise Time Filtering to Achieve Simple Models
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The Interconnect Modeling Company™
Correlation to Physical Structure
PCB section Cable section
Partition 1 Partition 2
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The Interconnect Modeling Company™
Differential TDR
Virtual ground plane Even and odd mode measurements
Cable: Z 0, tdR source
TD
R O
scill
osc
op
e F
ron
t Pa
ne
l
V incidentV reflected
DUT: Z D UT
V
V
Cable: Z 0, td
Virtual ground
R source
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The Interconnect Modeling Company™
Differential TDR Measurement Setup
Cable: Z 0, tdR source
TD
R O
scill
osc
op
e F
ron
t P
an
el
V incidentV reflected
V
V
Cable: Z 0, tdR source
Z DUT , tDUT
Z DUT , tDUT
Z termination
Z termination
Lines under test (DUT) are symmetrical TDR pulses are symmetrical TDR pulses arrive at the DUT at the same time
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The Interconnect Modeling Company™
Differential Line Model Partitioning
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The Interconnect Modeling Company™
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
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The Interconnect Modeling Company™
Model Verification
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The Interconnect Modeling Company™
LC Computation From Even-Odd Analysis
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The Interconnect Modeling Company™
Questions? Comments?
Please help us make this presentation better!
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The Interconnect Modeling Company™
Supplementary Information
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The Interconnect Modeling Company™
Parasitic Inductance
dtVVV
ZdttZL
t
t
shortrefTDR
t
t 2
1
2
1
0)(
Cable: Z 0, tdR source
TD
R O
scill
osco
pe F
ront
P
anel
V incident
V reflectedV
L
V TDR
V ref shortL
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The Interconnect Modeling Company™
Parasitic Capacitance
dtVVVZ
dttZ
Ct
t
TDRopenref
t
t 2
1
2
1 0
1
)(
1
Cable: Z 0, tdR source
TDR
Osc
illos
cope
Fro
nt
Pan
el
V incident
V reflectedV C
Open
V TDR
V ref open
C
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The Interconnect Modeling Company™
Symmetrical Coupled Line Model
Assumptions:– the lines are symmetrical– TDR pulses are symmetrical
– TDR pulses arrive at the lines at the same time at the
beginning of both lines
Board lines
TDR source 1
TDR source 2
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The Interconnect Modeling Company™
Symmetrical Coupled Line Model
Zodd, Zeven, todd, teven:
directly obtained from odd and even impedance profiles
Z 0
Z 0 -Z odd /2, t odd
Z even /2, t even
Z odd , t odd
Z odd , t odd
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The Interconnect Modeling Company™
3-Line Symmetrical Coupled Line Model
! assume: todd=teven !
Alternatively, for differential lines: tmutual = todd
evenoddZZZ 0
Z
Z
Z mutual
evenZZ
Z 0
Z 0
Note:
oddeven
evenoddm ZZ
ZZZ
2
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The Interconnect Modeling Company™
Even/Odd vs. Common/Differential
mtot
mselfodd CC
LLZ
mtot
mselfeven CC
LLZ
mtotmselfodd CCLLlt mtotmselfeven CCLLlt
oddaldifferenti ZZ 2 evencommon ZZ
oddaldifferenti tt evencommon tt
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The Interconnect Modeling Company™
Frequency or Time Domain?
VNA: Steady state
measurements Very high dynamic
range “Black box” S-
parameter results Single-element
modeling capabilities
TDR: Transient
measurements Windowing capability Can model complex
structures– but – multiple
reflections impede accuracy
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The Interconnect Modeling Company™
Frequency or Time Domain
Interconnect properties– Typically are complex multi-element structures– Interconnects are broadband structures – Measurements do not require high dynamic
range –Interconnects are NOT resonant structures (normally; however, a package cavity may become such structure)
– Measurement DO require good spatial (time) resolution–Length of a lumped discontinuity can be very short (~ps)