In Situ de Embedding
In Situ de Embedding
In Situ de Embedding
(ISD)
Ching-Chao Huang
huang@ataitec.com
www.ataitec.com
Outline
What is causality
How to identify non-causal S parameter
Why does S parameter violate causality
What is In-Situ De-embedding (ISD)
Why do other de-embedding methods give causality error
How to use ISD to…
De-embed crosstalk by a single trace test coupon
De-embed long traces and extract a small DUT
Improve results for USB Type C compliance testing
Comparison of ISD with TRL, AFR and simulation
Mobile-apps-like SI tools: ISD, ADK and X2D2
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VNA and S parameter
T (period)
f (frequency) = 1/T
S21
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What is S parameter
Sij ≤ 1
Sij (dB ) = 20 × log10 Sij ≤ 0 dB
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What is a Touchstone (.sNp) file
: : :
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What is causality
cau·sal·i·ty
noun
1. the relationship between cause and effect.
2. the principle that everything has a cause.
In other words:
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How to identify non-causal S parameter
* Delay waveform by
1ns to see if tools
do not show before
time zero.
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Why does S parameter violate causality
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What is de-embedding
to VNA
lead-in trace test board lead-out trace lead-in trace test board
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Why do most de-embedding tools give
causality error
Most tools use test coupons directly for de-
embedding, so difference between actual fixture
and test coupons gets piled up into DUT results.
DUT
- Test coupons
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What is In-Situ De-embedding (ISD)
• Mobile-Apps-like SI
software as easy to use
2 as 1-2-3.
• Causal by construction.
3
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What is “2x thru”
SMA DUT
SMA DUT
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Why ISD is more accurate and saves $$$
More board space - Multiple test coupons Only one 2x thru test coupon is needed.
are required. Test coupon is used only for reference, not
Test coupons are used directly for de- for direct de-embedding.
embedding. Actual DUT board impedance is de-
All difference between calibration and embedded.
actual DUT boards gets piled up into DUT Inexpensive SMAs, board materials (FR4)
results. and loose-etching-tolerance can be used.
Expensive SMAs, board materials (Roger) ECal can be used for fast SOLT calibration.
and tight-etching-tolerance are required.
Reference plane is in front of SMA.
Impossible to guarantee all SMAs and traces
are identical (consider weaves, etching, …) De-embedding is made easy as 1-2-3 with
only two input files: 2x thru and DUT board
Time-consuming manual calibration is (SMA-to-SMA) Touchstone files.
required. More information: Both de-embedding and
Reference plane is in front of DUT. DUT files are provided as outputs.
* TRL = Thru-Reflect-Line
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Example 1: Mezzanine connector
ISD vs. TRL
SMA Mezzanine
connector
(DUT)
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DUT results after ISD and TRL
Which one is more accurate?
Non-causal
ripples
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Converting S parameter into TDR/TDT
shows non-causality in TRL results
Non-causal
Non-causal
?
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Zoom-in shows non-causal TRL results
in all IL, RL, NEXT and FEXT
TRL causes time-domain errors of 0.38% (IL),
25.81% (RL), 1.05% (NEXT) and 2.86% (FEXT) in
this case*.
Non-causal
* The percentage is
larger with single-bit
Non-causal response and/or
faster rise time.
Non-causal
Non-causal
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How did ISD do it?
2x thru and
fixture have
different
impedance.
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TRL can give huge error in SDD11 even with
small impedance variation*
De-embedding
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Example 2: Mezzanine connector
Extracting DUT from a large board
Fixture
Mezzanine
connector
2x thru (DUT)
(12” total)
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ISD can use a .s4p file of 2x thru for
de-embedding
TRL would have required many long and coupled
traces.
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ISD can even use a .s2p file of 2x thru to de-
embed crosstalk…
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ISD allows a large demo board to double
as a characterization board
ISD de-embeds fixture’s impedance regardless of
2x thru’s impedance.
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Example 3: USB type C mated connector
ISD vs. AFR
3
7
5 2x thru
3
1
1
2
DUT 6 Fixture
4 8
2 4
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DUT results after ISD and AFR
Which one is more accurate?
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Converting S parameter into TDR/TDT
shows non-causality in AFR results
Counter-clockwise phase angle is another indication
of non-causality.
Ripples
Non-causal
Counter-
clockwise
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De-embedding affects pass or fail of
compliance spec.
ISD improves IMR and IRL (from compliance tool).
ISD AFR
Spec
-0.6
-0.8
-1.0
-40
-18
-44
-44
IL RL IL RL
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Example 4: Resonator
ISD vs. AFR vs. simulation
2x thru
DUT
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SDD21
ISD correlates with simulation better
Ripples
Red – Simulation
Yellow – After AFR
Red – Simulation
Yellow – After ISD
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SDD11
ISD correlates with simulation much better
Red – Simulation
Yellow – After AFR
Red – Simulation
Yellow – After ISD
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SCC11
ISD correlates with simulation much better
Red – Simulation
Yellow – After AFR
Red – Simulation
Yellow – After ISD
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ADK and X2D2
Mobile-apps-like SI tools
VNA 3D Solver
Material property
S S S
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Summary
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