the interconnect modeling company™ high-speed interconnect measurements and modeling dima...
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The Interconnect Modeling Company™
High-Speed Interconnect Measurements and Modeling
Dima SmolyanskyTDA Systems, Inc.
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
The Interconnect Modeling Company™
Signal Integrity Issues
Propagation delay Reflections Crosstalk
SPICE/IBIS simulations and accurate interconnect models are required
Loss Ground bounce Dispersion
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
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
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)
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
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
The Interconnect Modeling Company™
TDR Multiple Reflection Effects
Z0 Z1 Z2 Z3 Z4
Vtransmitted1
Vreflected1 Vreflected2
t0
Time Direction of propagation
The Interconnect Modeling Company™
Z-line Example
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
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
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
The Interconnect Modeling Company™
Partitioning Impedance Profile Waveform
The Interconnect Modeling Company™
Composite Model Generation
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Model Simulation and Verification
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Using Rise Time Filtering to Achieve Simple Models
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Correlation to Physical Structure
PCB section Cable section
Partition 1 Partition 2
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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
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
The Interconnect Modeling Company™
Differential Line Model Partitioning
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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Model Verification
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LC Computation From Even-Odd Analysis
The Interconnect Modeling Company™
Questions? Comments?
Please help us make this presentation better!
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Supplementary Information
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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
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
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
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
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
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
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
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)