SpaceWire Physical Layer Issues Shaune Allen September 10, 2004 ITAR SENSITIVE These items are licensed by the United States for ultimate destination European Space Agency (and related entities e.g. contractors and subcontractors). Diversion, retransfer, disclosure, or use contrary to applications specified in NASA agreement without prior U.S. authorization are prohibited. Page 1
SpaceWire Physical Layer Issues! Shielding Configuration Background and Rationale behind current configuration Supporting Test Results! Connector Specification SpaceWire connectors have known issues - Not impedance matched to the cable - Handling (Mechanical) issues Need space-qualified matched impedance connector - Efforts to identify an alternative or replacement space-qualified connector Page 2
SpaceWire Testing! NASA has contracted or performed testing to evaluate the SpaceWire specifications! Testing includes: Differential Impedance Insertion Loss Return Loss Skew - Pair to Pair - Within Pair Eye Patterns - Conformance to LVDS Threshold Levels - Jitter Bit Error Rate Measurement Shielding Effectiveness - Wire Injection Method Near End Crosstalk (NEXT) Ground Bounce Susceptibility LVDS Common Mode Range Common Mode Rejection Testing done with Data/Clock - Data/Strobe testing will be performed in the future Page 3
Cable Assembly Configurations Tested! Conforming! Inner shield tied together and to pin 3 of the connector on both ends of the cable assembly and isolated from outer shield that connects to the connector shell! Inner shields tied together and to outer shield which is tied to the connector shell on both ends of the cable assembly! Conforming with outer shield removed Page 4
What are the Requirements?! Cable Length: 10m suggested (should vs. shall)! Wire Guage of signal wires 28 AWG consisting of seven strands of 36 AWG wire (5.2.21)! Jitter(not specified; recommended maximum 20% National Semiconductor AN-1088)! Bit Error Rate(not specified; generally <1.0E-12)! Shielding Effectiveness (not specified ESCC 3902-003 4.8.17)! Near End Crosstalk (NEXT) (not specified)! Differential Impedance 100 ± 6 Ω (5.2.3.11)! Insertion Loss (not specified)! Return Loss (not specified)! Skew Pair to Pair: <0.15ns/m (5.2.4.15) Within Pair: <0.1ns/m (5.2.3.12, 5.2.4.15)! LVDS (6.1) LVDS Threshold Levels (± 100mV)! LVDS Common Mode Range (not specified; generally ±1V) Page 5
NEXT on Connector with Adaptor 0 Near End Crosstalk Construction: -20 Lot no.: Sample length (m): 20m -40 16.07.2004 M. Bluhm Near End Crosstalk [db] -60-80 Remark: Space Wire Cable Assembly B (20m) Test Dynamik Bulkhead Connector 9-pin MDM 9-pin Subminature D-Type 15-pin High Density -100-120 W.L. Gore & As s ociates GmbH Nordring 1 D-91785 P leinfeld Tel.(09144)601-0 Frequency [MHz] -140 30 227 424 621 818 1015 1212 1409 1606 1803 2000 Page 6
NEXT of Connector/Adaptor/Cable 0 Near End Crosstalk Construction: -20 Lot no.: Sample length (m): 20m 16.07.2004-40 M. Bluhm Near End Crosstalk [db] -60-80 Bulkhead Connector (Driven 5-9 quiet 1-6) 9-pin MDM (Driven 5-9, quiet 1-6) Remark: Space Wire Cable Assembly B (20m) 9-pin Subminature D-Type 15-pin High Density -100-120 W.L. Gore & Associates GmbH Nordring 1 D-91785 P leinfeld Tel.(0914 4 )601-0 Frequency [MHz] -140 30 227 424 621 818 1015 1212 1409 1606 1803 2000 Page 7
NEXT of Connector/Adaptor/Cable 0 Near End Crosstalk Construction: -20 Lot no.: Sample length (m): 20m 16.07.2004-40 M. Bluhm Near End Crosstalk [db] -60 Remark: Space Wire Cable Assembly B (20m) -80-100 Bulkhead Connector (Driven 5-9 quiet 4-8) Bulkhead Connector (Driven 5-9 quiet 1-6) Bulkhead Connector (Driven 5-9 quiet 1-6) 9-pin MDM (Driven 5-9, quiet 1-6) Frequency [MHz] W.L. Gore & Associates GmbH Nordring 1 D-91785 P leinfeld Tel.(09144)601-0 9-pin Subminature D-Type -120 15-pin High Density 30 227 424 621 818 1015 1212 1409 1606 1803 2000 Page 8
Conforming PTP Cable Assembly 5 5 Dout- Din+ 1 1 9 9 Dout+ Din- 6 6 4 4 Sout- Sin+ 2 2 8 8 Sout+ Sin- 7 7 to Tx Signal Gnd 3 3 GROUND GROUND 3 3 to Tx Signal Gnd 7 7 Sin- Sout+ 8 8 2 2 Sin+ Sout- 4 4 6 6 Din- Dout+ 9 9 1 1 Din+ Dout- 5 5 Sockets Pins Pins Sockets Page 9
Crosstalk! SpaceWire cable not significant contributor! Crosstalk due to connector (and connection)! Is the SpaceWire connector good enough? Dependant on pin configuration! No SpaceWire NEXT Specification Should one be defined???! TIA/EIA-644-A specifies NEXT of 36.8dB at 50 MHz for four twisted pairs with an outer shield! What is a good number?? Our results indicate <-30dB over the entire range (30MHz to 2 GHz) Page 10
Summary! User community needs background on SpaceWire inner shield grounding configuration! Although the SpaceWire connector is sufficient, a mechanically robust and matched impedance connector would improve performance and ease concerns! Need a mechanism within the standard process for deviation Alternative Connectors Wire Gauge Length (Jitter, Skew)! Communication regarding available SpaceWire commercial products! How do we proceed? Page 11