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					International SpaceWire Conference 2008
 Nov.5 2008




  Evaluation and Analysis of Connector Performance
            for the Spacewire Back Plane


     Koji Shibuya Keitaro Yamagishi Hideyuki Oh-hashi
               Seiichi Saito Masaharu Nomachi



                                                        1
               Contents

1.   Introduction
2.   Connector Evaluation Board
3.   Transmission Characteristics Evaluation
4.   Crosstalk Evaluation
5.   Eye-Pattern Waveform Analysis
6.   Conclusion



                                               2
      1. Introduction
SpaceWire backplane system


         Driver          Receiver



                         Daughter board




                         Connector

     Backplane System        Backplane




                                          3
                         1. Introduction
             SpaceWire backplane connectors


             Impedance
              Mismatch




                                       Crosstalk




-Connectors which have been selected by the space qualified are
NOT designed for high-speed Signal Transmission purpose.
     impedance mismatching and crosstalk are generated

Evaluation and Analysis of Connector Performance is
important.                                                   4
               2. Connector Evaluation Board
        Evaluation system for a backplane connector



                                                       PCB2
                                                  (Daughter board)




   PCB1
(Backplane)
              Connector for spacewire backplane


  - PCB1 corresponds to a backplane.
  - PCB2 corresponds to a daughter board.
                                                               5
2. Connector Evaluation Board
     Measurement Setup




                                6
             3. Transmission Characteristics Evaluation
Pin assignment for the transmission characteristics evaluation

                                                                    Edge of
                                                                    daughter board

A                B              C                     D




 E                   F                    G                     H
                                Daughter board
                                                          D/H
                                                          C/G
    Differential Pairs        Connector
                                                          B/F
                                                          A/E
    GND Pins

                                          Backplane
                                                                                7
                           Side view of evaluation board
                             3. Transmission Characteristics Evaluation

Measurement Results of Return Loss and Insertion Loss
             0                                                    0


       -10                                                        -5
Sdd11 (dB)




                                                     Sdd21 (dB)
                                                                       A
       -20
                         A                                  -10        B
                         B                                             C
                         C                                             D
                         D                                             E
                         E                                             F
                         F                                  -15        G
       -30               G                                             H
                         H

             0       2       4       6      8   10                 0   2     4        6      8     10
                          Frequency (GHz)                                  Frequency (GHz)
                 Differential return loss (Sdd11)            Differential insertion loss (Sdd21)

        -Differences between different pin assignments become
        remarkable in frequency range higher than 1GHz.

        - The pin assignments using the long pins for signals cause
        characteristic degradation.                                                                     8
                     4. Crosstalk Evaluation
        Pin assignment for crosstalk evaluation

 No GND pins around the victim


                                           Differential Pairs (Victim)

                                           GND Pins

GND pins existing around the victim        Aggressive signal pins

                                           Static signal pins

   a             b               c




   d             e                                                       9
                                       4. Crosstalk Evaluation
                               Measurement Results of Crosstalk
             0                                                         0
                      Port 1                Port 2                         a      Port 1         Port 2
                                                                           b
       -20            Port 3                Port 4               -20       c          GND
                                                                           d      Port 3         Port 4
Sds13 (dB)




                                                          Sds13 (dB)
                                                                           e
       -40                                                       -40

       -60                                                       -60

       -80                                                       -80
             0   2     4        6       8            10                0   2     4          6    8        10
                     Frequency (GHz)
                                                                               Frequency (GHz)
No GND pins around the victim                             GND pins existing around the victim

The pin assignment of the GND pins around the differential
pair is effective to reduce the crosstalk from the other signal.
( 15dB or more )

Crosstalk can be dramatically reduced by ground pins around
victim.                                                     10
                     5. Eye-Pattern Waveform Analysis
                            Waveform Simulation Model
           Signal
           Source
                                                                  Received
                                                                   signal
 Differential                                                  Differential
Transmission                       Differential               Transmission
    Lines                         Transmission                    Lines
                                      Lines
                Connector                         Connector
                 model                             model




         Assuming High Speed Back Plane System
           - 50 cm total trace
           - 3.125 Gbps data rate
           - 2 connectors
         Pin Assignment
           - E (shortest pin) and H (longest pin)                             11
             5. Eye-Pattern Waveform Analysis
                    Results of Analysis




      Pin Assignment E                Pin Assignment H
         (Short pins)                    (Long pins)




- Eye-Pattern of pin assignments E is better for transmission
                                                                12
                         6. Conclusion
1. The pin assignments using the long pins for signals cause
    characteristic degradation.

2. The pin assignment of the GND pins around the differential
pair is effective to reduce the crosstalk from the other signals.

3. The eye-pattern waveforms were shown by the simulation.
     the 3Gbps backplane transmission is possible using the
connector selected by the space qualified design.

The connector selected by the space qualified design can use
for the system of over Gbps high speed signal transmission
via the backplane by suitable pin assignment design.

                                                                    13

				
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