de-embedding techniques in advanced design...
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De-embedding Techniques in
Advanced Design System
De-embedding Techniques in ADS
Page 2
Agenda
• Why de-embedding?
• 2-port de-embedding
• Mixed mode S-parameters
• Four port de-embedding
• TRL based de-embedding
• Summary
De-embedding Techniques in ADS
Page 3
Non Insertable Measurements
Die
Ball PadProbe SMA
Reference Plane
Reference Plane
Board Response = Total Response – Probe SMA Response
Require accurate modeling of Probe SMA response
De-embedding Techniques in ADS
Page 4
DUT with Test Fixtures
Requires test fixture: Not a part of the back plane structure
How to remove test fixture effects from the overall measurement?
De-embedding Techniques in ADS
Page 5
Backplane measurementsTest Fixture
Backplane Response = Total Response – Test Fixture Response
Sometimes it is not feasible to remove test fixture effects using various calibration techniques
De-embedding Techniques in ADS
Page 6
De-embedding Requirements in EM SimulationMoving Reference Plane
Sometimes it is not feasible to move the reference plane in EM tools.
De-embedding Techniques in ADS
Page 7
What is De-embedding?
De-embedding is a mathematical process that removes the effects of unwanted portions of the structure that are embedded in the measured data by subtracting their contribution.
“Real” DUT SP = Measured SP – Fixture CharacteristicDe-embedding : Negating effects of unwanted portion
H ACTIVE CHANNEL
RESPONSE
STIMULUS
ENTRY
INSTRUMENT STATE
R CHANN
EL
THP-IB
STATUS
NETWORK ANALYZER
50 MHz-20GHz
PORT 2
PORT 1
THRUDUT
Before De-embedding
Requires accurate fixture model
• Empirical models from measured data
• Simulation based models
After De-embedding
De-embedding Techniques in ADS
Page 8
Why use S-Parameters?relatively easy to obtain at high frequenciesrelate to familiar measurements (gain, loss, reflection coefficient ...)can cascade S-parameters of multiple devices to predict system performancecan compute H, Y, or Z parameters from S-parameters if desiredcan easily import and use S-parameter files in our simulation tools
Incident TransmittedS 21
S 11
Reflected S 22
Reflected
Transmitted Incident
b 1
a 1b 2
a 2
S 12
DUT
Port 1 Port 2
S 11 = ReflectedIncident
=b1a 1 a2 = 0
S 21 =TransmittedIncident
=b2a 1 a2 = 0
S 22 = ReflectedIncident
=b2a 2 a1 = 0
S 12 =TransmittedIncident
=b1
a 2 a1 = 0
De-embedding Techniques in ADS
Page 9
De-embedding two port networkTo de-embed with transfer scattering parameters, the matrix math is straightforward…
11 12 12 21 11 22 11
21 22 2221
11
T T S S S S ST T SS
−⎛ ⎞⎡ ⎤ ⎡ ⎤= ⎜ ⎟⎢ ⎥ ⎢ ⎥−⎣ ⎦ ⎣ ⎦⎝ ⎠
Network a Network b
Ttotal = Ta Tb
Ta = Ttotal Tb-1
Tb = Ta Ttotal-1
Order is very important
11 12 12 11 22 12 21
21 22 2122
11
S S T T T T TS S TT
−⎛ ⎞⎡ ⎤ ⎡ ⎤= ⎜ ⎟⎢ ⎥ ⎢ ⎥−⎣ ⎦ ⎣ ⎦⎝ ⎠
Relationship between S and T-Parameters
De-embedding Techniques in ADS
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Getting DUT data using De-embedding
a3
[ TA ] [ TD ] [ TB ]
2-portDUT
a0
b0
a1
b1
b2b3
a2
MEASURED ACTUAL
[ ] [ ][ ][ ] [ ] [ ] [ ][ ]1 1;m A D B D A m BT T T T T T T T− −= =
Let us build a sample network to demonstrate the de-embedding process in ADS
De-embedding Techniques in ADS
Page 11
De-embedding Example - DUT2-portDUT
a
0
b
0
a
1
b
1
b2
b
3
a
2
High speed connector model
De-embedding Techniques in ADS
Page 12
Representing the Test Fixture 2-portDUT
a
0
b
0
a
1
b
1
b2
b
3
a
2
Test fixture
De-embedding Techniques in ADS
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Test Fixture plus ConnectorConnectorTest Board In Test Board Out
b
3
a
0
b
0
2-portDUT
a
1
b
1
b2
a
2
De-embedding Techniques in ADS
Page 14
Using 2-Port ADS De-embedding ComponentConnectorTest Board In Test Board Out
2-portDUT
a
1
b2
Comparison with original Connector Model(Magnitude and Phase Response)
De-embed Component
De-embed Component
De-embedding Techniques in ADS
Page 15
Backplane Performance Evaluation
Backplane and Daughter card
De-embedding Techniques in ADS
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The Simulation Circuit Problem
Backplane
4” Trace
SMA
Connector
D/C
4”Tr
ace
SMA
4” Trace
SMA
Connector
D/C
4”Trace
SMA
Conn
ecto
r “M
odel”
PROBLEM: Need to remove effect of these SMA’s!
X” Trace (4” or 10”)
Connector “Model”
De-embedding Techniques in ADS
Page 17
Solve the Problem with De-embedding block
Connector “M
odel”Co
nnec
tor “
Mod
el”
Effect of SMA’s removed by de-embedding.
Backplane
4” TraceConnector
4”Tr
ace
SMA
4” TraceConnector
4”Trace
SMA
X” Trace (4” or 10”)
D/C D/C
De-embedding Techniques in ADS
Page 18
Simulation vs. Measured Data( Only two port de-embedding element was used)
ScopeEye
ΔV=0.415 V
Teradyne + 18” at 2.5Gb/sD(sim vs. scope) < 1%
Teradyne + 18” at 3.125Gb/sΔ(sim vs. scope) = 6%
ΔV=0.251 V
ADS Eye Simulation
ΔV=0.236 V
ADS Eye Simulation
ΔV=0.417 V
De-embedding Techniques in ADS
Page 19
DUT
Test Board To Be De-embed
Differential Pair
Measurement Reference Plane
Four Port Measurements
Four Port Fixture: Four Port De-embedding
Need to account for coupling
Differential-mode signal
Common-mode signal
Differential tocommon-mode
conversion
DUT Reference Plane
De-embedding Techniques in ADS
Page 20
Single Ended Simulation of Differential Pins
De-embedding Techniques in ADS
Page 21
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
44434241343332312423222114131211
SSSSSSSSSSSSSSSS
ＰＯＲＴ１
ＰＯＲＴ２
ＰＯＲＴ３
ＰＯＲＴ４
Nodal S-parameter
SDD11 SDD12
SDD21 SDD22
SDC11 SDC12
SDC21 SDC22
SCD11 SCD12
SCD21 SCD22
SCC11 SCC12
SCC21 SCC22
ＰＯＲＴ１ ＰＯＲＴ２
Diff Mode
Common Mode
Mixed Mode S-parameter
What is Mixed Mode S-parameters?
reciprocal
De-embedding Techniques in ADS
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Driving Mixed Mode S-Parameter from Single Ended Measurements
De-embedding Techniques in ADS
Page 23
Direct Mixed Mode S-Parameter Simulation
Differential Mode to Differential Mode S-parameter
Common Mode to Common Mode S-parameter
Balun Balun
Comparing two techniques
Advantage – Mixed Mode S-Parameter Optimization
De-embedding Techniques in ADS
Page 24
Connector With Fixture ModelConnectorTest Board In Test Board Out
b
3
a
0
b
0
2-portDUT
a
1
b
1
b2
a
2
De-embedding Techniques in ADS
Page 25
Using ADS Four Port De-embedding Component
Comparison with Connector Model Only Response
ConnectorTest Board In Test Board Out
De-embed
ComponentDe-embed Component
Accounts for coupling between feed transmission lines
De-embedding Techniques in ADS
Page 26
De-embedding ComponentsStandard de-embedding components in ADS
•One Port de-embedding
• Two Port de-embedding
New standard de-embedding components in ADS2006A
Aggressor and Victim differential pair characterization requires
multi-port De-embedding• Four port de-embedding
• Six port de-embedding
• Eight port de-embedding
• Twelve port de-embedding
Requirements:Measured/Simulated S-parameters to be available
De-embedding Techniques in ADS
Page 27
Test Cases?
Fixture S-parameter cannot be obtained directly?
Can one use TRL calibration standards?
De-embedding Techniques in ADS
Page 28
TRL measurement based De-embedded Component• Used when the test fixture S-parameter response is not available• Ability to fabricate test fixtures and calibration standard• Test fixtures are created using the same feed line structure as in the TRL standard.
De-embedding Techniques in ADS
Page 29
DUT & Fixture/Calibration KitTRL
Calibration Kit DUT Board
DUT
Material - FR4Er=4.2Thickness=0.6mmTand=0.025T=18[mm] (Metal Thickness)S=5.8*107[S/m](Conductivity)
TRL calibration standard.
De-embedding Techniques in ADS
Page 30
Design of TRL Calibration kit
Reflect is open
(Open is more suitable than Short)
ThruConnector
*Red line is reference plane of DUT
Length of Line must be determined by frequency range
20deg < f < 160deg
* This condition must meet on both Common/Diff modes
LineLine
Ze,Zo
ADS Line calc ADS Line calc
Reflection
“Thru” is mirror connection of feed lines
De-embedding Techniques in ADS
Page 31
Why ADS based TRL De-embedding?
Feed line coupling not
accounted for
Some test fixture might have significant coupling.
How one can account for the coupling effects?
De-embedding Techniques in ADS
Page 32
Custom De-embedding using TRL Calibration Standards
Coupled Feed line1
DUT with “Coupled” feed lines 4-port De-embedding
Our “New” 4-port De-embedding modelcreated using C code
Custom solution- Not available as standard feature of ADS
Contact EEsof for details
Coupled Feed line2
DUT
Feed lines can beAsymmetric •Can not use TRL on Si Substrate
De-embedding Techniques in ADS
Page 33
“New” 4-port De-embedding verification resultsComparison between De-embedded S-parameters & DUT without feed lines.
2 types of S-parameters are completely identical!!
De-embedding Techniques in ADS
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Compare to ADS modelDUT部
DUT
Simulated (ADS Coupled line model)
Measured
De-embedding Techniques in ADS
Page 35
Conclusion• Demonstrates the use of ADS for a typical SI problem
• Provide powerful measurement based modeling
• ADS De-Embedding capabilities • Two port de-embedding
• Powerful Multi-port de-embedding essential for bus/ differential bus
( one pair, two pair, & three pair )
• TRL calibration based de-embedding
• ADS has been used for SI design for over 20 years
• ADS has a multitude of accurate built in models
• ADS allows you to build accurate physical models
• ADS brings IP, simulation and measurement together
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