12006 MAPLD International Conference SpaceWire 101 Seminar

DESIGN CHALLENGES OF AN ADVANCED SPACEWIRE ASSEMBLY FOR HIGH SPEED

INTER-UNIT DATA LINK

Joachim Mueller, W.L. Gore&Associates

email: jmueller@wlgore.com

Internet: www.wlgore.com

22006 MAPLD International Conference SpaceWire 101 Seminar

Motivation

System design solutions for advanced communications missions are driving up symbol/data rates with:

- Increasingly demanding skew and delay requirements

- Critical design issue for the cable assemblies and for an electrical matched and balanced connector in particular.

The cable assemblies are used to transfer various types of signals between units on board the spacecraft, e.g.:

- Reference/synchronisation clock signals

- High data rate serial links such as SpaceWire

- Digitally modulated baseband signals (QPSK, 8PSK, etc) These interfacing functions need a differential mode of transmission

capable of maintaining high integrity in the process.

32006 MAPLD International Conference SpaceWire 101 Seminar

Four Shielded Twisted Pairs High Performance GoreTex

Dielectric

Overall braided EMI shield

Performance Table

Cable Drawing

SpaceWire Cable Design

42006 MAPLD International Conference SpaceWire 101 Seminar

Connector Performance Issues

Triax Contact Micro D-Sub

Commonly used Connector interfaces show strong impedance mismatch

52006 MAPLD International Conference SpaceWire 101 Seminar

Connector Performance Issues

Connector performance has a strong impact on the signal transmission at frequencies above 30MHz.

Assembly shows non-monotonic attenuation characteristic.

Matched Connector interface required.

Signal Attenuation vs. Frequency

Bulk Cable

Assembly

62006 MAPLD International Conference SpaceWire 101 Seminar

Symmetrical Connector Interface

Impedance vs. Length4 and 5-way Twinax Connector

72006 MAPLD International Conference SpaceWire 101 Seminar

Advanced Interconnect Performance

Attenuation of 2m long SpaceWire Cable Assembly

Insertion Loss [dB/20m]f [MHz] 70 250 400AWG 26 -4.96 -9.69 -12.71AWG 28 -7.23 -14.46 -18.81

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

1 41 81 121 161 201 240 280 320 360 400

Frequency [MHz]

Ins

ert

ion

Lo

ss

[d

B]

Clock

Pair 1

Pair 2

Pair 3

Pair 4

GSC-10-82738-00 SN 1

M. Bluhm

W.L. Gore & Associates GmbHNordring 1D-91785 PleinfeldTel.(09144)601-0

Remark:

Construction:

Lot no.:

Insertion Loss

Sample length (m):

1243222

Attenuation of 20m long SpaceWire Cable Assembly

82006 MAPLD International Conference SpaceWire 101 Seminar

Reflection Loss Measurements

Reflection loss S11 Space Wire Test Assembly

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

1 31 61 91 121 151 180 210 240 270 300

f [MHz]

Re

turn

Lo

ss

[d

B/1

0m

]

Line 1

Line 2

Line 3

Line 4

Clock

Line < 100 MHz < 200 MHz < 300 MHz01 26dB 26dB 19dB02 30dB 30dB 25dB03 27dB 27dB 27dB04 27dB 27dB 25dB

Clock 30dB 32dB 32dB

Reflection Loss

92006 MAPLD International Conference SpaceWire 101 Seminar

Skew Measurements

Test Results: Total pair to pair skew space wire cables 273 ps/10mWithin pair skew max. space wire cables 290 ps/10mWithin pair skew clock cables 31 ps/10m

Line Phase [°] Delay [s]01 1469.47 40,819E-0902 1461,57 40,599E-0903 1459,65 40,546E-0904 1469,43 40,817E-09

Delta +/- 9.81 273 E-12

Phase Delay

Line Within pair skew01 290 ps/10m02 240 ps/10m03 230 ps/10m04 101 ps/10m

Clock Cable 30 ps/10m

Within Pair Skew

102006 MAPLD International Conference SpaceWire 101 Seminar

Connector NEXT

112006 MAPLD International Conference SpaceWire 101 Seminar

Crosstalk Results

SpaceWire cable not significant contributor to crosstalk

Crosstalk due to 9-pin Microminiature D-type connector (and connection)- Cross talk between Data and Strobe high (~20dB)- Crosstalk between Strobe pairs high (~20dB)

122006 MAPLD International Conference SpaceWire 101 Seminar

Shielding Measurements

-200

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

0,01 0,10 1,00 10,00 100,00 1000,00 10000,00

Frequency f [MHz]

Sh

ield

ing

Eff

ecti

ven

ess a

s [

dB

]

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

1E+1

1E+2

1E+3

1E+4

1E+5

ZT

[m

Oh

m/m

]

Space Wire

Clock Cable

Space Wire Test Assembly

24.10.2003

M. Bluhm

W.L. Gore & Associates GmbHNordring 1D-91785 PleinfeldTel.(09144)601-0

measured according to IEC60966-1

Paratron ist eingetragenes WarenzeichenDer W.L. Gore & ASSOCIATES GmbH

Remark:

R DC = 7 mOhm

Construction:

Lot no.:

Shielding Effectiveness for 1m Assemblies: >100dB@ 100MHz

> 60dB@ 1GHz

132006 MAPLD International Conference SpaceWire 101 Seminar

Eye Pattern Measurement

Eye Pattern @200Mbps, 10m, AWG26 Eye Pattern @200Mbps, 10m, AWG28

Eye Height [mV] Jitter peak to peak [ps]AWG28 257 420AWG26 392 140

LVDS requirements: Eye Height: 200 mV,Jitter:1 ns @ 200 Mbit/s

142006 MAPLD International Conference SpaceWire 101 Seminar

Eye Pattern Measurement

Eye Pattern @60Mbps, 10m AWG28 Eye Pattern @60Mbps, 20m, AWG28

Eye Height [mV] Jitter peak to peak [ps]10m 453 33020m 247 1386

LVDS requirements: Eye Height: 200 mV,Jitter:3.3ns @ 60 Mbit/s

152006 MAPLD International Conference SpaceWire 101 Seminar

Summary

Technical issues with a symmetrical cable interconnect using a Triax contact has been discussed.

A new design with a light and compact twinax contact has been introduced.

The electrical Performance in terms of Impedance, Insertion Loss, Return Loss, Crosstalk, Skew, Eye Pattern and Shielding has been presented

The performance of the new symmetrical cable interconnect is adequate for frequencies up to 2GHz and higher.