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Eric Bogatin 2009
Slide -1
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Building Confidence in Simulation Tools
Dr. Eric Bogatin, Signal Integrity Evangelist,
Bogatin Enterprises, www.beTheSignal.com
eric@beTheSignal.com
Eric Bogatin 2009
Slide -2
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Outline
• Role of simulation tools
• A calibration process
� Compared to analytical exact expressions
� Compared to other simulators
� Compared to well characterized test vehicles
� Compared to test vehicles
• A simple Dk, Df measurement process
Eric Bogatin 2009
Slide -3
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Why SI/PI Engineering is Hard
• Over riding product design goals
� Meet higher performance specs
� Meet shrinking schedules
� At lower cost
• Pick any two- it’s easy
• Doing all three- it’s hard
Eric Bogatin 2009
Slide -4
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
General Design Methodology
• Two categories of products
� Performance driven
� Cost-performance
• An efficient methodology;
� Identify the SI problems
� Find the root cause
� Establish design guidelines to minimize them
� “correct by design”: use analysis tools to develop prepre--layoutlayout design rules specific to your design
� Use post layoutpost layout verification tools to efficiently spin virtual prototypes
} Understand the essential principles
Eric Bogatin 2009
Slide -5
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
The Role of Analysis Tools
• Pre-layout phase
� Explore design tradeoffs
� Explore technology options
� Establish specific design rules/constraints for each custom design
• Post layout phase
� Final verification
� Robust to manufacturing variations
� Don’t pay extra for insurance (un-needed margin)
• Simulation/analysis as risk reduction
� Same risk level, lower added margin, lower added cost
Added margin �C
ost � simulation R
isk �
Eric Bogatin 2009
Slide -6
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Design Cultures
“This is the one. We want you to pray for this one.”
Build it and test itEngineering discipline
model
measure simulate
create
“Test in performance” “Design in performance”
expertise
money
critical mass
“short term pain for
long term gain”leadership
Eric Bogatin 2009
Slide -7
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Leverage Appropriate Analysis Tools
Rules of Thumb: Feeds your
intuition, useful for order of
magnitude estimating
1st order approximations:
Analytic approximations,
useful for quick estimates and
early design tradeoffs
Numerical simulation: field
solver, parasitic extraction,
SPICE, IBIS simulations,
can base a design on this
Ac
cu
rac
y
Effort required to get answerexpertise
moneytime
Eric Bogatin 2009
Slide -8
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
The Design Process
From Here To Here Or Here
?
Eric Bogatin 2009
Slide -9
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Creativity is the key ingredient to the design process
IntuitionIntuition is the designer’s most important tool
Eric Bogatin 2009
Slide -10
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
One Role of Numerical Simulation
Tools: When Accuracy Counts
Characteristic impedance
Low
control
limit
High
control
limit
Accuracy error
Dis
trib
ution
Eric Bogatin 2009
Slide -11
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
How to Evaluate the Accuracy of a
Simulation Tool?
1. Compare the results to analytically exact equations
2. Compare the results to other, well established industry standard simulation tools
3. Compare the results to well characterized test vehicles
4. Compare the results to typical interconnect structures
Eric Bogatin 2009
Slide -12
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Characteristic Impedance of Twin
Rods and Ansoft Field Solver
0
50
100
150
200
250
300
350
400
450
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Rod Radius (mm)
Ch
ara
cte
ris
tic
Im
pe
da
nc
e
(OH
ms
)
analytic
field solver
−
+
ε= 1
22ln
1202
0r
s
r
sZ
r
r r
s
s = 30 mm
0.0%
0.2%
0.4%
0.6%
0.8%
1.0%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Radius (mm)
Ab
so
slu
te E
rro
r
Eric Bogatin 2009
Slide -13
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Comparing Polar Si9000 to Ansoft SI2D
0
1020
3040
50
60
70
8090
100110
120
0 2 4 6 8 10 12 14 16 18 20
Line Width, mils
Ch
ara
cte
ris
itc
Im
pe
da
nc
e, o
hm
s
Ansoft
Polar
0%
1%
2%
3%
4%
5%
0 2 4 6 8 10 12 14 16 18 20
Line Width, milsA
bs
olu
te E
rro
r
H1 = 5 milsEr1 = 4T1 = 1.4 milsW1 = W2 = variable.
Eric Bogatin 2009
Slide -14
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Comparing the Polar Si9000 to
Agilent ADS
-1%
0%
1%
2%
3%
4%
0 2 4 6 8 10 12 14 16 18 20
Line Width, mils
Ab
so
lute
Err
or
Absolute error for field solvers ~ <1%
Eric Bogatin 2009
Slide -15
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Calculated Single-ended S-Parameters: Comparing Agilent ADS and Polar Si9000
H1 = 5 milsEr1 = 4S1 = 5 milsW1 = W2 = 5 milsT1 = 0.7 milsDf = 0.02Length = 6 inches
2 4 6 80 10
-30
-20
-10
-40
0
freq, GHz
S-Parameter in dB
Return loss
Insertion loss
2 4 6 80 10
-50
-40
-30
-20
-10
-60
0
freq, GHz
S-P
arameter in dB S41
S31
Red is ADSBlue is Polar
Eric Bogatin 2009
Slide -16
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Calculated Differential S-Parameters: Comparing Agilent ADS and Polar Si9000
2 4 6 80 10
0.85
0.90
0.95
1.00
1.05
0.80
1.10
freq, GHz
Delay in nsec
Common signal delay
Differential signal delay
2 4 6 80 10
-30
-20
-10
-40
0
freq, GHz
Differential S-Parameter in dB
SDD21
SDD11
Comparative accuracy is within pen width
Red is ADSBlue is Polar
Eric Bogatin 2009
Slide -17
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
“Typical” test vehicle
• Stripline
• Closely spaced
• Nominal values: � T= 1.4 mils
� H1 = H2 = 10 mils
� w = 8.6 mils
� s = 8.4 mils
� Dk = 4.5
� Df = 0.02
Eric Bogatin 2009
Slide -18
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Converting Test Line Parameters
into S-Parameters
Eric Bogatin 2009
Slide -19
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
0.5 1.0 1.5 2.0 2.50.0 3.0
42
44
46
48
50
52
54
40
55
time, nsec
Single-ended Impedance, ohms
0.5 1.0 1.5 2.0 2.50.0 3.0
0
20
40
-20
60
time, nsec
Near End Cross Talk, x1000
0.5 1.0 1.5 2.0 2.50.0 3.0
-0.0
0.2
0.4
0.6
0.8
-0.2
1.0
time, nsec
Transmitted Single-ended Signal
0.5 1.0 1.5 2.0 2.50.0 3.0
0
2
4
6
8
-2
10
time, nsec
Far End C
ross Talk, x 1000
Initial Comparison:
Single-Ended Performance
measured
simulated
One conclusion: simulator is accurate to ~ 10%
Eric Bogatin 2009
Slide -20
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Alternative Conclusions
• What is simulated is not what is measured
� SMA launch not in simulation
� ¼ inch uncoupled trace feed not in simulation
• The as designed parameters are not the same as the as manufactured parameters
� H, w
� Dk, Df
Eric Bogatin 2009
Slide -21
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Including SMA Launch and Feed
Effects
0.5 1.0 1.5 2.0 2.50.0 3.0
42
44
46
48
50
52
54
40
55
time, nsec
Single-ended Impedance, ohms
0.5 1.0 1.5 2.0 2.50.0 3.0
-0
10
20
30
40
50
-10
60
time, nsec
Near End C
ross Talk, x1000
0.5 1.0 1.5 2.0 2.50.0 3.0
-0.0
0.2
0.4
0.6
0.8
-0.2
1.0
time, nsec
Transmitted S
ingle-ended Signal
0.5 1.0 1.5 2.0 2.50.0 3.0
0
2
4
6
8
10
-2
12
time, nsec
Far End Cross Talk, x 1000
measured
simulated
Eric Bogatin 2009
Slide -22
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
What about Cross Section and
Materials?
• Cross section shows� H: 10 mils nominal � 10.2 mils actual
� W: 8.6 mils nominal � 8 mils actual
� S: 8.4 mils nominal � 9 mils actual
• Materials :� Dk from fab: 4.5 � 4.0 (measured)
� Df assumed 0.02, stays the same
Eric Bogatin 2009
Slide -23
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Single Ended Response
0.5 1.0 1.5 2.0 2.50.0 3.0
42
44
46
48
50
52
54
40
55
time, nsec
Single-ended Impedance, ohms
0.5 1.0 1.5 2.0 2.50.0 3.0
-0
10
20
30
40
50
-10
60
time, nsec
Near End C
ross Talk, x1000
0.5 1.0 1.5 2.0 2.50.0 3.0
-0.0
0.2
0.4
0.6
0.8
-0.2
1.0
time, nsec
Transmitted Single-ended Signal
0.5 1.0 1.5 2.0 2.50.0 3.0
2
4
6
8
0
10
time, nsecFar End Cross Talk, x 1000
measured
simulated
What accounts for the slightly different slopes in NEXT?
Eric Bogatin 2009
Slide -24
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Asymmetry:
Welcome to the Real World
0.5 1.0 1.5 2.0 2.50.0 3.0
42
44
46
48
50
52
54
56
58
40
60
time, nsec
Z11_meas
Z22_meas
TDR response measured from opposite ends: T11, T22
0.5 1.0 1.5 2.0 2.50.0 3.0
0
10
20
30
40
50
-10
60
time, nsec
Near End C
ross Talk, x1000
NEXT response measured from opposite ends: T31, T42
Eric Bogatin 2009
Slide -25
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
2 4 6 8 10 12 14 16 180 20
-50
-40
-30
-20
-10
-60
0
freq, GHz
Return Loss, db
2 4 6 8 10 12 14 16 180 20
-20
-10
-30
0
freq, GHz
Insertion loss, dB
2 4 6 8 10 12 14 16 180 20
-50
-40
-30
-20
-10
-60
0
freq, GHz
S31, near end cross talk, db
2 4 6 8 10 12 14 16 180 20
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.0
1.0
freq, GHzDelay, nsec
Frequency Domain, Single-ended
BW of the simple transmission line model ~ 12 GHz
measured
simulated
Eric Bogatin 2009
Slide -26
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Measure Dk, Df of Materials
• Practical: easy, routine, robust
• Many standards
• IPC is generating new methods
• Fundamental issue: removing connector effects
• A solution:� Build uniform line with a few precision discontinuities
� Model the launches
� Model the discontinuities
� Fit to entire topology and Dk, Df values
� Instant evaluation of the quality of the connector/launch model
Eric Bogatin 2009
Slide -27
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Simple Test Structures
SMA launches on back sideNon-uniform launches
Precision discontinuities spaced 3 inches in the line
Eric Bogatin 2009
Slide -28
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.60.0 2.8
35
40
45
50
30
55
time, nsec
Z11_meas
Z22_meas
Measured TDR Response
From port 1 side
From port 2 side
Note: - some asymmetry in the line- very symmetric launches
Eric Bogatin 2009
Slide -29
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Modeling an SMA-
or other Discontinuity
TD
1
10
1BW <
Len
For a general, non uniformnon uniform section:
Up to what frequency will a T model match its behavior?
As long as Len < 1/10th λ
secnin6
LenTD =
Len
6.0BW < inches
BW
6.0Len <
For a 10 GHz BW, longest non-uniform element should be < 60 mils
With SMA length ~ 150 mils, and a 10 GHz BW, need no more than 3 T elements
Eric Bogatin 2009
Slide -30
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Circuit Topology to Fit:
10 different Parameters
ML1CTL_CTL62
ReuseRLGC=noRLGC_File=Layer=2
W=w_1 milLength=Len_c inSubst="Subst1"
ML1CTL_CTL80
ReuseRLGC=noRLGC_File=Layer=2
W=w_1 milLength=Len_b inSubst="Subst1"
ML1CTL_CTL68
ReuseRLGC=noRLGC_File=Layer=2
W=w_1 milLength=Len_a inSubst="Subst1"
CC7C=C_a pF
CC6C=C_a pF
Term
Term3
Z=50 Ohm
Num=3
TLINTL65
F=(1/TD_3b) GHzE=360Z=Z0_3b Ohm
TLINTL64
F=(1/TD_3a) GHzE=360Z=Z0_3a Ohm
Term
Term4
Z=50 Ohm
Num=4
TLINTL71
F=(1/TD_4b) GHzE=360Z=Z0_4b Ohm
TLINTL72
F=(1/TD_4a) GHzE=360Z=Z0_4a Ohm
TLINTL77
F=(1/TD_4c) GHzE=360Z=Z0_4c Ohm
TLINTL78
F=(1/TD_3c) GHzE=360Z=Z0_3c Ohm
SMA launch Len = 3 inches
6 parameters;Zo, TD x 3 Parameter nominal extracted
W 13.1 mils 12.5H 10 mils 10.5Dk 4.5 3.94
Df 0.02 0.017
Eric Bogatin 2009
Slide -31
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
TDR Response
0.5 1.0 1.5 2.0 2.5 3.0 3.50.0 4.0
10
20
30
40
50
0
60
time, nsec
Z11_meas
Z11_sim
Eric Bogatin 2009
Slide -32
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
S-Parameter Match
2 4 6 80 10
-30
-20
-10
-40
0
freq, GHz
dB(S11_meas)
dB(S
11_sim
)
2 4 6 80 10
-100
0
100
-200
200
freq, GHz
phase(S11_meas)
phase(S11_sim
)
2 4 6 80 10
-5
-4
-3
-2
-1
-6
0
freq, GHz
dB(S21_meas)
dB(S
21_sim
)
2 4 6 80 10
-100
0
100
-200
200
freq, GHz
phase(S21_meas)
phase(S21_sim
)
measuredsimulated
Eric Bogatin 2009
Slide -33
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Conclusions
• Accuracy of field solver can be ~ 2% at BW > 10 GHz between field solver simulations and well characterized test vehicles
• Requires
� Accurate materials properties
� As manufactured cross section
• Even using constant Dk, Df values
• The Real World is more complex than we would like it to be
� Uniform transmission lines aren’t
� As manufactured features not equal to as specified features
� Dielectric thicknesses as manufactured not equal to as specified
� Etch back of signal lines variable
� Launches may have asymmetry
Eric Bogatin 2009
Slide -34
www.BeTheSignal.com
DL-210 Building Confidence on Simulation Tools
Concerns for the Future
• Moving the industry toward “engineering discipline”
• Overcoming the barriers
expertisemoney
critical mass
“short term pain for long term gain”leadership
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