Group/Presentation Title Agilent Restricted Month ##, 200X TDR/TDT and S Parameters Measurement...

Group/Presentation TitleAgilent Restricted Month ##, 200X

TDR/TDT and S ParametersMeasurement Applications and Examples

86100C Option 202


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


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


Agilent’s Signal Integrity Portfolio

86100C

86100C

Opt201 202

Opt 200 201


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


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


Simple & Intuitive User Interface


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


Using markers to measure the characteristic impedance of a transmission line


Using advanced settings function to adjust the vertical scale to display the impedance directly


The same transmission line displayed on the impedance scale at 10 Ohms per division, with 50 Ohms in the center


High resolution TDR profile of a nominally uniform transmission line


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


TDR response with markers showing the beginning and end of the traces

TDR from reference open

TDR from 6 inch uniform line


TDR response of a uniform transmission line with two small reference pads, located on 4 inch centers


TDR response from a microstrip with 2 reference pads, using markers to measure the round trip time delay


Stripline construction and extracting the bulk dielectric constant

2803.11

velocity

Dk

stripline


Effective Dielectric Constant in microstrip

Return

microstrip

Dk~ 4

Dk = 1

2803.11

velocity

Dkeff


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


TDR response from a uniform transmission line having a small test pad


Using the excess reactance feature to extract the capacitance of a test pad


Using markers to extract the excess capacitance of the SMA launch


Using markers to extract the excess capacitance of two corners


Using markers to extract the excess inductance of a short gap in the return path


Using markers to extract the excess inductance of a large gap in the return path


Using markers to extract the excess inductance of an axial lead termination resistor


Using markers to extract the excess inductance of a SMT termination resistor


DUTIncident wave

Reflected wave

Transmitted wave

S11

S21

Incident wave

Reflected wave

Transmitted wave

TDR

TDTt

t

DUT

Relationship of TDR and S Parameters


Converted S11 of the SMT termination resistor


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


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


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.


Configuration for TDR/TDT Measurements

TDR stimulus

TDR responseTDT response


User Wizard for TDR/TDT operation


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


TDR/TDT response converted into frequency domain for return loss/insertion loss

Insertion loss of reference thru

Insertion loss of DUTReturn loss of DUT


Return and insertion loss of a 24 inch interconnect on a motherboard with two daughtercards

Insertion loss of DUT

Return loss of DUT


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


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


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


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


Configuration for two port TDR measurements

TDR stimulus

TDR responseTDT response

FEXTNEXT

Active or aggressor line

Quiet or victim line


Measurement of the NEXT on a quiet line using the marker


Measuring both the NEXT and FEXT with the second channel in the TDR

Measured at near end and at far end, all ends terminated


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


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


Measured NEXT and FEXT in a 24 inch long trace on a mother board, with all ends terminated

FEXT

NEXT

TDR response


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


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


TDR of a single ended transmission line crossing gaps in the return path, showing the inductive discontinuities


Measured ground bounce on the quiet line from gaps in the return path

Near end noise

TDR response


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


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


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


Configuration for differential pair characterization

Line 1

Line 2

Differential stimulus

Line 1

Line 2

Common stimulus


DTDR Set up screen for differential measurements


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


Three impedances of a single line displayed directed on an impedance scale

Odd mode impedance


Even mode impedance


Measured odd mode impedance of each line in a differential pair, displayed directly on an impedance scale


Measured even mode impedance of each line in a differential pair, displayed directly on an impedance scale


Measured differential impedance of a pair of microstrip traces, displayed directly on an impedance scale


Measured common impedance of a pair of microstrip traces, displayed directly on an impedance scale


Comparison of the measured single ended impedance and odd mode impedance of a single line in a long motherboard trace


Odd mode impedance


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


Measured reflected common signal from a coax to twisted pair transition with an incident common signal

Differential impedance

Common impedance


Measured differential impedance profile of a differential pair crossing a wide gap in the return path

Single ended TDR

Differential TDR


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


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


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


Case Study – Typical PC Board


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


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


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


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)



•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




•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 Board traces


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


Viewing Correction Prior to Reference PlaneMeasured loads at front panel – scale at 2 ohms/div’n

Only noise from digital filter


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



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 Board traces


Comparison of Differential Stimulus

Agilent steps agree within 0.5-0.6 mV

Another supplier’s steps agree within 9-10mV


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


Backplane Trace Layout

Layer

1

2

3

4

Tx1Rx1

Tx2Rx2

Tx3Rx3

Tx4Rx4

Channel PairsTest Ports

1 2

3 4

Test Ports


Assess Channel Impedance Using TDR

Connector

Launch

Ckt card vias

Backplane vias

Yellow is

Layer 1

Green is

Layer 4

60

50

40


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


Assess Channel Using TDT

•Blue is Layer 1 TDT•Red is Layer 4 TDT•Channels are different by 129ps


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


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.


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


Backplane Trace Connections - Crosstalk

Layer

1

2

3

4

Tx1Rx1

Tx2Rx2

Tx3Rx3

Tx4Rx4

Channel PairsTest Ports

12

34

Test Ports


Assess Crosstalk

Typical spec in standards is 20-26dB

Blue is Layer 1

Red is Layer 4

Group/Presentation Title Agilent Restricted Month ##, 200X TDR/TDT and S Parameters Measurement...

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Transcript of Group/Presentation Title Agilent Restricted Month ##, 200X TDR/TDT and S Parameters Measurement...