1. DESIGN CHALLENGES OF AN ADVANCED SPACEWIRE ASSEMBLY FOR HIGH SPEED INTER-UNIT DATA LINK
Joachim Mueller, W.L. Gore&Associates
Internet:

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

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

5. Connector Performance Issues
Bulk Cable
Assembly
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

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

7. Advanced Interconnect Performance
Attenuation of 2m long SpaceWire Cable Assembly
Insertion Loss [dB/20m]
f [MHz]
AWG
AWG
Attenuation of 20m long SpaceWire Cable Assembly

8. Reflection Loss Measurements

9. Skew Measurements

10. Connector NEXT

11. SpaceWire cable not significant contributor to crosstalk
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: 100MHz
> 1GHz

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

14. Eye Pattern Measurement
LVDS requirements:
Eye Height: Mbit/s
Eye 10m AWG28
Eye 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.