group/presentation title agilent restricted month ##, 200x tdr/tdt and s parameters measurement...
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Group/Presentation TitleAgilent Restricted Month ##, 200X
TDR/TDT and S ParametersMeasurement Applications and Examples
86100C Option 202
Group/Presentation TitleAgilent Restricted Month ##, 200X
Outline
•Importance of TDR and S-
parameter measurements
•One port TDR
•Two port TDR
•Case study – PC board
•Case study - backplane
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Impedance Problems are Everywhere!
Connector
Custom Connector
Cable
DIMM PCB
Motherboard BackplaneRouterStorage Area Network
IC package
Components
SubassembliesSystems
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Required Parameters by StandardStandard Max Freq,
GHzImpedance Return
LossAttenu-ation
Crosstalk
PCI Express Gen 2 5 X X X
PCI Express 1.25 X X X X
PCI-X X X
Serial Attached SCSI 7.5 X
IPC N/A X
Fully Buffered DIMM 2.4 X
IEEE 802.3ae X X
Infiniband 6.3 X X X
Serial ATA 4.5 X X X
EIA-364-90 N/A X X
EIA-108 N/A X X
HDMI 4.1 X X X
DVI 4.1 X
Firewire 8 X X X
USB 2.0 1.3 X X
RapidIO 8
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Agilent’s Signal Integrity Portfolio
86100C
86100C
Opt201 202
Opt 200 201
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New 86100C Capabilities
Feature Benefit
TDR Calibration and N1024 Calibration Kit
•Higher yields through more accurate measurements
•Quickly see impact of rise times
S-parameters with new wizard*•Time and frequency domain with one button click
Export to Touchstone files*•Use S-parameters to model devices and systems
Corrected Impedance Profile* (peeling)
•Compensate measurements for large discontinuities
Minimum/maximum/average•Quickly compare values against standards limits
Excess reactance•Obtain value for equivalent circuit components
* Indicates feature is provided in Option 202
Group/Presentation TitleAgilent Restricted Month ##, 200X
Applications for the One Port TDR (Slides 8-32)
• Measuring characteristic impedance and uniformity of a transmission line
• Measuring time delay of a transmission line
• Accurate measurement of signal speed in a transmission line
• Extracting bulk dielectric constant of the laminate
• Building a model of a discontinuity
• Building a high bandwidth model of a component
• Directly emulating the impact on a signal with the system rise time from a discontinuity
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Simple & Intuitive User Interface
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Measured TDR response - microstrip transmission line
TDR from reference open
TDR from DUT
Top trace is the reflection from the end of the cableBottom trace is the reflected signal from the DUT
Group/Presentation TitleAgilent Restricted Month ##, 200X
Using markers to measure the characteristic impedance of a transmission line
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Using advanced settings function to adjust the vertical scale to display the impedance directly
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The same transmission line displayed on the impedance scale at 10 Ohms per division, with 50 Ohms in the center
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High resolution TDR profile of a nominally uniform transmission line
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High resolution TDR response from each end of the same uniform transmission line, verifying the impedance variation is real
TDR from left end launch
TDR from right end launch
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TDR response with markers showing the beginning and end of the traces
TDR from reference open
TDR from 6 inch uniform line
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TDR response of a uniform transmission line with two small reference pads, located on 4 inch centers
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TDR response from a microstrip with 2 reference pads, using markers to measure the round trip time delay
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Stripline construction and extracting the bulk dielectric constant
2803.11
velocity
Dk
stripline
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Effective Dielectric Constant in microstrip
Return
microstrip
Dk~ 4
Dk = 1
2803.11
velocity
Dkeff
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3.5
3.6
3.7
3.8
3.9
4.0
4.1
4.2
4.3
4.4
4.5
2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5Effective Dielectric Constant
Bu
lk D
iele
ctr
ic C
on
sta
nt
Using a field Solver to Back Out the Bulk Dielectric Constant from the effective dielectric constant
Dkeff = 3.34
Dkbulk = 4.48
Group/Presentation TitleAgilent Restricted Month ##, 200X
TDR response from a uniform transmission line having a small test pad
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Using the excess reactance feature to extract the capacitance of a test pad
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Using markers to extract the excess capacitance of the SMA launch
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Using markers to extract the excess capacitance of two corners
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Using markers to extract the excess inductance of a short gap in the return path
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Using markers to extract the excess inductance of a large gap in the return path
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Using markers to extract the excess inductance of an axial lead termination resistor
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Using markers to extract the excess inductance of a SMT termination resistor
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DUTIncident wave
Reflected wave
Transmitted wave
S11
S21
Incident wave
Reflected wave
Transmitted wave
TDR
TDTt
t
DUT
Relationship of TDR and S Parameters
Group/Presentation TitleAgilent Restricted Month ##, 200X
Converted S11 of the SMT termination resistor
Group/Presentation TitleAgilent Restricted Month ##, 200X
ADS model of resistor and the measured and simulated S parameters
Z0 = 48.8 OhmsTD = 0.06 nsec R = 48.5 OhmsL = 0.489 nH
LL1
R=L=L nH
RR1R=R Ohm
TLINTL1
F=(1/TD) GHzE=360Z=Z0 Ohm
TermTerm2
Z=50 OhmNum=2
1 2 3 4 5 6 7 8 9 10 11 12 13 140 15
-100
0
100
-200
200
freq, GHz
S11 p
hase
, deg
1 2 3 4 5 6 7 8 9 10 11 12 13 140 15
-40
-30
-20
-10
-50
0
freq, GHz
S11, dB
Group/Presentation TitleAgilent Restricted Month ##, 200X
Emulating system rise time responses for a 200 mil long neck down region with effective rise times = 40, 100, 200, 500 psec
RT = 40 psec
RT = 100 psec
RT = 200 psecRT = 500 psec
Group/Presentation TitleAgilent Restricted Month ##, 200X
Applications for the 2-port TDR (Slides 34-70)TDR/TDT
1. Measuring insertion loss and return loss2. Extracting dielectric constant of the laminate3. Extracting dissipation factor of the laminate4. Measuring the bandwidth of the interconnect5. Identifying design features that contribute to excessive loss
TDR/cross talk6. Measuring NEXT7. Measuring FEXT8. Emulating FEXT for different system rise times9. Identifying design features that contribute to NEXT10. Exploring the impact of terminations on NEXT and FEXT11. Measuring ground bounce12. Identifying design features that contribute to ground bounce13. Emulating ground bounce noise for different system rise times
Differential TDR (DTDR)14. Measuring each of the five impedance associated with a differential pair15. Measuring the degree of coupling between lines in a differential pair16. Measuring the differential impedance of a twisted pair cable17. Measuring the reflected noise of a differential signal crossing a gap in the return path18. Emulating the reflected noise at the system rise time for a differential signal crossing a gap19. Measuring the mode conversion in a differential pair20. Identifying specific physical features that contribute to mode conversion in a differential pair.
Group/Presentation TitleAgilent Restricted Month ##, 200X
Configuration for TDR/TDT Measurements
TDR stimulus
TDR responseTDT response
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User Wizard for TDR/TDT operation
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Example of TDR/TDT response from 8 inch long microstrip transmission line on 20 mV/div and 500 psec/div scales
Transmitted response
Reflected response
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TDR/TDT response converted into frequency domain for return loss/insertion loss
Insertion loss of reference thru
Insertion loss of DUTReturn loss of DUT
Group/Presentation TitleAgilent Restricted Month ##, 200X
Return and insertion loss of a 24 inch interconnect on a motherboard with two daughtercards
Insertion loss of DUT
Return loss of DUT
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ADS modeling of a uniform 8 inch long microstrip, showing the bandwidth of the simple model to be ~12 GHz
2 4 6 8 10 12 14 16 180 20
-30
-20
-10
-40
0
freq, GHz
S21, dB
TermTerm4
Z=50 OhmNum=4
TermTerm3
Z=50 OhmNum=3
ML1CTL_CTL1
ReuseRLGC=noRLGC_File=Layer=1W=W1 milLength=Len1 inSubst="Subst1"
Dk = 4.43H1 = 60 milsTanD = 0.025Len = 8 inches W1 = 125 mils
BW of the model is ~ 12 GHz
Group/Presentation TitleAgilent Restricted Month ##, 200X
Measured insertion loss of a reference thru, a uniform line (DUT-1) and a uniform line that is part of a differential pair (DUT-2)
Insertion loss of reference thru
Insertion loss of DUT-1
Insertion loss of DUT-2
Group/Presentation TitleAgilent Restricted Month ##, 200X
ADS model of the 9 inch long trace, modeling the coupling to the adjacent, quiet line, showing the bandwidth of the model to be ~ 8 GHz
2 4 6 80 10
-30
-20
-10
-40
0
freq, GHz
S21, dB
2 4 6 80 10
-100
0
100
-200
200
freq, GHz
S21 p
hase
, degre
es
ML2CTL_CCLin1
ReuseRLGC=noRLGC_File=Layer=1S=S1 milW=W1 milLength=Len1 inSubst="Subst1"
TermTerm4
Z=50 OhmNum=4
TermTerm3
Z=50 OhmNum=3
RR2R=50 Ohm
RR1R=50 Ohm
Dk = 4.43H1 = 60 milsTanD = 0.025Len = 9 inches W1 = 125 milsS1 = 115 mils
Group/Presentation TitleAgilent Restricted Month ##, 200X
2 4 6 80 10
-30
-20
-10
-40
0
freq, GHzS
21, dB
2 4 6 80 10
-30
-20
-10
-40
0
freq, GHz
S21, dB
Changing Separation between the two transmission lines showing the impact on the insertion loss dip
Similar coupled striplinew = 125 mils, s = 115 mils
50 75 100 125 150
Simulated stripline insertion loss
Edge to edge spacing, in mils
Group/Presentation TitleAgilent Restricted Month ##, 200X
Configuration for two port TDR measurements
TDR stimulus
TDR responseTDT response
FEXTNEXT
Active or aggressor line
Quiet or victim line
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Measurement of the NEXT on a quiet line using the marker
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Measuring both the NEXT and FEXT with the second channel in the TDR
Measured at near end and at far end, all ends terminated
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Emulating the FEXT with different system rise time responses with RT = 100, 200, 500, 1nsec
Measured at near end, far ends of active and quiet lines open
RT = 1 nsec RT = 500 psec
RT = 200 psecRT = 100 psec
Group/Presentation TitleAgilent Restricted Month ##, 200X
Measured TDR response of 24 inch long trace in a mother board using markers to measure the impedance in the daughter card and mother board
Group/Presentation TitleAgilent Restricted Month ##, 200X
Measured NEXT and FEXT in a 24 inch long trace on a mother board, with all ends terminated
FEXT
NEXT
TDR response
Group/Presentation TitleAgilent Restricted Month ##, 200X
Measured cross talk in quiet line with worst case termination
FEXT
NEXT
TDR response (port 1)
Measured at far end (port 2)
1
2
open
open
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Tightly coupled pair of transmission lines with small gaps in the return path that will generate ground bounce
Short gap in the return path
Longer gap in the return path
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TDR of a single ended transmission line crossing gaps in the return path, showing the inductive discontinuities
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Measured ground bounce on the quiet line from gaps in the return path
Near end noise
TDR response
Group/Presentation TitleAgilent Restricted Month ##, 200X
Emulating impact of rise time on the ground bounce noise in a pair of coupled lines with a rise time of 500 psec
Near end noiseRT = 500 psec
TDR responseRT = 500 psec
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Measured TDR response of a single line crossing a large gap in the return path and the ground bounce noise in the quiet line
Near end noise
TDR response
50 mV/divFEXT FEXT
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Emulating ground bounce noise from large gap at rise times of 100 psec and 1 nsec
Near end noiseRT = 1 nsec
TDR responseRT = 1 nsec
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Configuration for differential pair characterization
Line 1
Line 2
Differential stimulus
Line 1
Line 2
Common stimulus
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DTDR Set up screen for differential measurements
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Measured TDR response of a single transmission line configured for the even mode, single ended and odd mode
Odd mode impedance
Single ended impedance
Even mode impedance
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Three impedances of a single line displayed directed on an impedance scale
Odd mode impedance
Single ended impedance
Even mode impedance
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Measured odd mode impedance of each line in a differential pair, displayed directly on an impedance scale
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Measured even mode impedance of each line in a differential pair, displayed directly on an impedance scale
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Measured differential impedance of a pair of microstrip traces, displayed directly on an impedance scale
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Measured common impedance of a pair of microstrip traces, displayed directly on an impedance scale
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Comparison of the measured single ended impedance and odd mode impedance of a single line in a long motherboard trace
Single ended impedance
Odd mode impedance
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Measured differential impedance of two different twisted pair cables connected to a coax launch
Twisted pair in telephone cable
Twisted pair in cat V Ethernet cable
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Measured reflected common signal from a coax to twisted pair transition with an incident common signal
Differential impedance
Common impedance
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Measured differential impedance profile of a differential pair crossing a wide gap in the return path
Single ended TDR
Differential TDR
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Emulating the differential impedance profile of a differential signal crossing a large gap at four different rise times
10 Ohms/div
RT = 100 psec RT = 200 psec
RT = 500 psecRT = 1 nsec
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Measured mode conversion from differential to common signal due to an asymmetry on one line in a pair
Received common signal component
DTDR response
Open far endSmall capacitive asymmetry on one line
SMA launch
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Measured mode conversion on a differential pair when the capacitive asymmetry is moved from one line to the other
Capacitive asymmetry on line 1
Capacitive asymmetry on line 2
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Case Study – Typical PC Board
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Ability of TDR Calibration to Improve TDR Rise Time through Lossy or Dispersive Paths
•Calibrated at end of 1m RF cables, measure shorts for fall time•Shorts and fall time are chosen to eliminate effect of fringing capacitance at the end of an unterminated line
Edge speed has improved from 79 to 25ps
Yields very clean pulse
Group/Presentation TitleAgilent Restricted Month ##, 200X
Ability of TDR Calibration to Improve TDR Rise Time through Lossy or Dispersive Paths
•Calibrated at right end of adapter (female 3.5mm)
•Placed shorts there to characterize fall time
•Improved edge speed from 553ps to 83ps
•Much cleaner step
Differential PC boardtraces
Group/Presentation TitleAgilent Restricted Month ##, 200X
Benefits of TDR Calibration•Ability to correct for TDR step aberrations
•Ability to improve edge speeds through lossy and dispersive lines
•These two abilities yield better measurement accuracy of impedances in typical measurement situation (not at the front panel of the test instrument), particularly when looking at closely-spaced discontinuities
•These same benefits are available when calibrating at probe tip using a calibration substrate
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Ability of TDR Calibration to Improve Accuracy through Lossy or Dispersive Paths
•Calibrated at front panel of TDR module; measured as two single ended-traces to transition into differential lines•For balanced lines, can add two single-ended measurements to obtain differential (cal’d at 27.34 + 27.21 = 54.55 ohms; raw ~ 62 ohms)
Group/Presentation TitleAgilent Restricted Month ##, 200X
Ability of TDR Calibration to Improve Accuracy through Lossy or Dispersive Paths
•Calibrated at right end of cable (female SMA)
•Measured impedance of 32in board of 1/3 of differential trace
•Blue trace is uncalibrated; yellow trace is calibrated
•Note ability to more accurately see large discontinuities
Differential PC boardtraces
Group/Presentation TitleAgilent Restricted Month ##, 200X
Ability of TDR Calibration to Improve Accuracy through Lossy or Dispersive Paths
•Calibrated at right end of male-to-male adapter
•Measured impedance to third bend in differential trace
•Red trace is uncalibrated; yellow trace is calibrated
•Note ability to more accurately see large discontinuities
Differential PC boardtraces
Differential PC Board traces
Group/Presentation TitleAgilent Restricted Month ##, 200X
Comparison of Results
Reference Plane>> At Front Panel
End of 1m Cables
End of 1m Cables & 12in Board
Calibrated 54.5 58.1 76.0
Uncalibrated 62 67.2 92.2
Other TDR instruments in the industry which lack TDR calibration would roughly provide the uncalibrated results
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Viewing Correction Prior to Reference PlaneMeasured loads at front panel – scale at 2 ohms/div’n
Only noise from digital filter
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Viewing Correction Prior to Reference Plane
•Calibrated at right end of cable
•Measured 12in board
•No aberrations prior to reference plane at 5 ohms per division
Differential PC boardtraces
Group/Presentation TitleAgilent Restricted Month ##, 200X
Viewing Correction Prior to Reference Plane
•Calibrated at right end of male-to-male adapter
•Measured 32in board
•Note only ripple from digital filter (set at 10ohms per division to see impedance traces)
•Setting Effective Rise Time to >100ps eliminates ripple (compare to raw trace with fall time of ~550ps)
Differential PC boardtraces
Differential PC Board traces
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Comparison of Differential Stimulus
Agilent steps agree within 0.5-0.6 mV
Another supplier’s steps agree within 9-10mV
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Case Study - Channel
Increasing the Rate on a 3Gb/s Backplane
•XAUI at 3.125Gb/s
•Four layers, each with differential transmit & receive pairs
•16” length
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Backplane Trace Layout
Layer
1
2
3
4
Tx1Rx1
Tx2Rx2
Tx3Rx3
Tx4Rx4
Channel PairsTest Ports
1 2
3 4
Test Ports
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Assess Channel Impedance Using TDR
Connector
Launch
Ckt card vias
Backplane vias
Yellow is
Layer 1
Green is
Layer 4
60
50
40
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Via Stubs Create Capacitive Loads
How is a Via Stub Created?• Signal current splits in
two directions and sees two 50 ohm lines in parallel (25 ohms)
• Excess capacitance is created by a 25 ohm segment of equivalent circuit
• Reflections and poor signal integrity results
Better (no stub)
i
i
Poorer
(stub)
i
i1
i2
Layer 4
Layer 1
Group/Presentation TitleAgilent Restricted Month ##, 200X
Assess Channel Using TDT
•Blue is Layer 1 TDT•Red is Layer 4 TDT•Channels are different by 129ps
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Single-ended S-Parameters
Return Loss or TDR
Insertion Loss or TDT
Near End Crosstalk (NEXT)
Far End Crosstalk (FEXT)
Four-port single-ended device
Port 1
Port 3
Port 2
Port 4
Frequency Domain Parameters
Group/Presentation TitleAgilent Restricted Month ##, 200X
Single-ended and Differential S-Parameters
44434241
34333231
24232221
14131211
SSSS
SSSS
SSSS
SSSS
Stimulus
Re
spo
nse
Port 1
Single-ended
Port 3 Port 2 Port 4
Balanced
port 1
BalancedBalanced
port 2
21CC
11CC
21DC
11DC
S
S
S
22CC
12CC
22DC
12DC
S
S
S
SS
21CD
11CD
21DD
11DD
S
S
S
22CD
12CD
22DD
12DD
S
S
S
SS
Port 1 Port 1Port 2 Port 2
Differential-Mode Stimulus
Common-Mode Stimulus
Port 1
Port 2
Port 1
Port 2
Diff
ere
ntia
l-M
ode
Res
pons
e
Com
mon
-M
ode
Res
pons
e
Naming Convention:Smode res., mode stim., port res., port stim.
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Assess Channel Using S-parameters
•Can export data to Touchstone for analysis•Return loss is required by many standards•ISI usually increases with channel attenuation
•S11 is Layer 1 Return Loss•S33 is Layer 4 Return Loss •S21 is Layer 1 Attenuation•S43 is Layer 4 Attenuation•Layer 4 has 10-15dB more loss
Group/Presentation TitleAgilent Restricted Month ##, 200X
Backplane Trace Connections - Crosstalk
Layer
1
2
3
4
Tx1Rx1
Tx2Rx2
Tx3Rx3
Tx4Rx4
Channel PairsTest Ports
12
34
Test Ports
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Assess Crosstalk
Typical spec in standards is 20-26dB
Blue is Layer 1
Red is Layer 4