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DESIGN CHALLENGES OF AN ADVANCED SPACEWIRE ASSEMBLY FOR HIGH SPEED INTER-UNIT DATA LINK

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

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DESIGN CHALLENGES OF AN ADVANCED SPACEWIRE ASSEMBLY FOR HIGH SPEED INTER-UNIT DATA LINK

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  1. 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

  2. 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.

  3. Four Shielded Twisted Pairs High Performance GoreTex Dielectric Overall braided EMI shield SpaceWire Cable Design Performance Table Cable Drawing

  4. Micro D-Sub Connector Performance Issues Triax Contact • Commonly used Connector interfaces show strong impedance mismatch

  5. Connector performance has a strong impact on the signal transmission at frequencies above 30MHz. Assembly shows non-monotonic attenuation characteristic. Matched Connector interface required. Bulk Cable Assembly Connector Performance Issues Signal Attenuation vs. Frequency

  6. Symmetrical Connector Interface Impedance vs. Length 4 and 5-way Twinax Connector

  7. Advanced Interconnect Performance Attenuation of 2m long SpaceWire Cable Assembly Insertion Loss [dB/20m] f [MHz] 70 250 400 AWG 26 -4.96 -9.69 -12.71 AWG 28 -7.23 -14.46 -18.81 Attenuation of 20m long SpaceWire Cable Assembly

  8. Reflection Loss Measurements

  9. Skew Measurements

  10. Connector NEXT

  11. 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)

  12. Shielding Measurements Shielding Effectiveness for 1m Assemblies: >100dB@ 100MHz > 60dB@ 1GHz

  13. Eye Pattern Measurement LVDS requirements: Eye Height: 200 mV,Jitter:1 ns @ 200 Mbit/s Eye Pattern @200Mbps, 10m, AWG26 Eye Pattern @200Mbps, 10m, AWG28

  14. Eye Pattern Measurement LVDS requirements: Eye Height: 200 mV,Jitter:3.3ns @ 60 Mbit/s Eye Pattern @60Mbps, 10m AWG28 Eye Pattern @60Mbps, 20m, AWG28

  15. 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.

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