IEEE RTPGE

Rosenberger Hochfrequenztechnik GmbH & Co. KG

Automotive Datalinks over Twisted Quad Cabling

T. Müller, G. Armbrecht, S. Kunz

Thomas Müller 2

IEEE RTPGEOutline

� Automotive Datalinks over Twisted Quad Cabling� Twisted Quad fundamentals� Twisted Quad connector interface

� EMC� Coupling to adjacent systems

� Measuring EMC properties of components

� Linking mode conversion to radiation

� Summary

Thomas Müller 3

IEEE RTPGETwisted Quad Fundamentals

� Opposite conductors form a differential pair� Fields cancel each other > virtual ground plane� Independent transmission of two data streams over one cable� Second pair can also be used for remote powering devices� Compact size� Round shape without fillers (mechanically stable)

+-

+ -

Virt. GND Pair 1 Virt. GND Pair 2

Thomas Müller 4

IEEE RTPGETwisted Quad Fundamentals

� Typical insertion loss 1 dB/m @ 1 GHz� Low crosstalk� Bidirektional communication

up to 3 GBit/s over 10 m LVDS possible

Sdd21 [Pair 1]

f [MHz]

Inse

rtio

n lo

ss [

dB/m

]

0.1 1 10 100 10000.001

0.01

0.1

1

10

NEXT [Pair 1 to Pair 2]

f [MHz]

Sdd

21 (

near

-end

) [d

B]

0.1 1 10 100 1000-100

-90

-80

-70

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-40

-30

-20

-10

0

Orange: Cat 6aBlack: Cat 5

Thomas Müller 5

IEEE RTPGE

� Open interface (connectors are available from different vendors)

� Interface as described in automotiveIEEE 1394 Copper Automotive Standard(Supplement to IDB-1394) Project TS2008001

� Designed to meet automotive requirements� Electrical (e.g. ISO/IEC 60603-7-51 CAT 6a, LV213)

� Mechanical and environmental (forces, waterproofness, LV214, USCar)

� Fully automated assembly process

� EMC� Radial shielding contact

� Compatible with fully-shielded (braid + foil),semi-shielded (foil) and unshielded

STQ Connector Interface

Thomas Müller 6

IEEE RTPGEEMC – Coupling to adjacent systems

Ethernet Networking100Base-TX,BroadR-Reach

CommunicationGSM, UMTS, LTE,WLAN, Bluetooth,Car2X, …

BroadcastAM, FM, DVB-T,DAB(+)

TransientsElectronic enginecontrol, switchingpower supplies,processor clock

Video Linksup to 3Gbit/sAPIX, LVDS, MHL

HV-Traction networkElectric drives,auxiliary systems(48V-Powernet)

EMCNavigationGPS, Glonass,Galileo

BUS SystemsLIN, CAN, MOST,USB

Thomas Müller 7

IEEE RTPGE

Common to differential mode conversion

Differential mode signal behavior

Differential to common mode conversion

Common mode signal behavior

Differential In

SCD11SCD11 SCD12SCD12

SCD21SCD21 SCD22SCD22

SDC11SDC11 SDC12SDC12

SDC21SDC21 SDC22SDC22

SCC11SCC11 SCC12SCC12

SCC21SCC21

SDD11SDD11

SCC22SCC22

Port2Port1

Common In

Port2Port1

Diff

eren

tial O

ut

Por

t2P

ort1

Com

mon

Out

Por

t2P

ort1

SDD12SDD12

SDD22SDD22SDD21SDD21

Common to differential mode conversion

Common to differential mode conversion

Differential mode signal behaviorDifferential mode signal behavior

Differential to common mode conversion

Differential to common mode conversion

Common mode signal behaviorCommon mode signal behavior

Differential InDifferential In

SCD11SCD11 SCD12SCD12

SCD21SCD21 SCD22SCD22

SDC11SDC11 SDC12SDC12

SDC21SDC21 SDC22SDC22

SCC11SCC11 SCC12SCC12

SCC21SCC21

SDD11SDD11

SCC22SCC22

Port2Port2Port1Port1

Common InCommon In

Port2Port2Port1Port1

Diff

eren

tial O

utD

iffer

entia

l Out

Por

t2P

ort2

Por

t1P

ort1

Com

mon

Out

Com

mon

Out

Por

t2P

ort2

Por

t1P

ort1

SDD12SDD12

SDD22SDD22SDD21SDD21

Measuring EMC properties

� Coupling attenuation determines the EMC properties of a differential channel as the sum of� Differential to common mode conversion attenuation

� Shielding attenuation for screened cables

� Mode conversion measured withS-parameter measurements byNetwork Analyzer (NWA)� TCL (Sdc11)� TCTL (Sdc21)

� …

Thomas Müller 8

IEEE RTPGEMeasuring EMC properties

� Unbalance along the channel causesmode conversion

� Concentrated unbalance can be compensated(e.g. through optimized footprint design)

� Distributed unbalance is most critical(e.g. within cable)

0.1 1 10 100 1000-100

-90

-80

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-10

0Length imbalance of differential pair

f [MHz]

Equ

al L

evel

Tra

nsve

rse

Con

vers

ion

Tra

nsfe

r Lo

ss [

dB]

∆∆∆∆ l = 500 mm

∆∆∆∆ l = 200 mm

∆∆∆∆ l = 100 mm∆∆∆∆ l = 50 mm

∆∆∆∆ l = 20 mm∆∆∆∆ l = 10 mm

CAT 5/6a Limit

∆∆∆∆ l = 1 mm

0.1 1 10 100 1000-100

-90

-80

-70

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-40

-30

-20

-10

0Capacitance imbalance of differential pair

f [MHz]

Equ

al L

evel

Tra

nsve

rse

Con

vers

ion

Tra

nsfe

r Lo

ss [

dB]

CAT 5/6a Limit

∆∆∆∆ C = 0.1 pF

∆∆∆∆ C = 100 pF∆∆∆∆ C = 50 pF

∆∆∆∆ C = 20 pF∆∆∆∆ C = 10 pF∆∆∆∆ C = 5 pF

∆∆∆∆ C = 1 pF

∆∆∆∆ C = 2 pF

Thomas Müller 9

IEEE RTPGE

� Measure transmission path� Identify basic screening parameters

Measuring EMC properties

EMI Source

EMI-EMS Trans-

mission Path

EMIVictim

Interferencetransfer function

Operational system

Adjacent systemsubject to interference

Transmitter

(e.g. NWA Port1)

Transfer impedancescreening-/ coupling

attenuation

Receiver

(e.g. NWA Port2)

Thomas Müller 10

IEEE RTPGE

� Triaxial tube allows measuring screening properties of individualcomponents along the channel

Measuring EMC properties

Cable Inline connections Feed-throughs

Thomas Müller 11

IEEE RTPGE

� Allows measuring screening properties of individual components along the channel by means of triaxial measurements

� The DUT can be fed from the NWA in common mode or differential mode to measure screening- or coupling attenuation

� Also applicable for unshielded differential pairs

Measuring EMC properties

DUT Triaxial Tube Diff. / comm. Termination

Shielded ferrule

NWA

Coax toDifferential PCB

1

2

3

Thomas Müller 12

IEEE RTPGE

� Twisted Quad cable assembly measurement examples

� Measurement of screening attenuation not intended for unshieldedcables according to given standards

� Quality of shield may be adjusted by construction

Measuring EMC properties

0.1 1 10 100 1000 10000-120

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0

Frequency [MHz]

Scr

eeni

ng a

tten

uatio

n [d

B]

Semi-shieldedFully-shieldedUnshielded

Screening attenuation

Thomas Müller 13

IEEE RTPGE

� Twisted Quad cable assembly measurement examples

� Fully-shielded cables provide excellent coupling attenuation� Unshielded cables can provide noticeable performance, if the balance

throughout the channel is maintained (connector, cable, termination)� Semi-shielded cables may be a viable compromise

Measuring EMC properties

0.1 1 10 100 1000 10000-120

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0

Frequency [MHz]

Cou

plin

g at

tenu

atio

n [d

B]

Coupling attenuation

Semi-shieldedFully-shieldedUnshielded

Coupling attenuation

Thomas Müller 14

IEEE RTPGE

� Measure differentialand common modecoupling to striplinein a three port NWAmeasurement

� UTQ cable 1.7 m� First end connected

to ground plane� Second end floating

� Measure TCTL inin same setup

� Compare the resultswith triaxial tube

EMC – Linking mode conversion to radiation

1 2 3 4

DUT 1.7 m

NWA

floating 1 2 3 4grounded

Thomas Müller 15

IEEE RTPGEEMC – Linking mode conversion to radiation

� Small coupling at low frequencies due to limited coupling length� Resonances at quarter wavelength and odd multiples

100

101

102

103-120

-100

-80

-60

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-20

0

f [MHz]

com. mode coupling diff. mode coupling

Thomas Müller 16

IEEE RTPGEEMC – Linking mode conversion to radiation

� Coupling to stripline is linked to mode conversion properties of the DUT� Mode conversion as difference between differential and common mode

coupling can be reproduced� Triaxial tube is less dependent on setup (e.g. DUT length, coupling

length, grounding) and easier to handle (e.g. no need for shielded chamber)

100

101

102

103-80

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0

f [MHz]

TCTLStripline: diff. coupling - com. coupling Triaxial Tube: coupling attenuation - screening attenuation

Thomas Müller 17

IEEE RTPGESummary

� Twisted Quad cables are widely used for differential signal transmission within vehicles.

� In combination with the STQ connector interface the automotive requirements concerning mechanical and electrical properties are met.

� The EMC properties of components along the channel can be evaluated by measuring mode conversion and coupling attenuation by means of a triaxial tube.

� The grade of shielding may be adapted to bandwidth, topology andEMC-environment of the application to be implemented without the need to change the connector interface.