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DP83867ERGZ-S-EVM: AC coupling

Part Number: DP83867ERGZ-S-EVM

Hello experts,

I got some question about SGMII design from customer.
Could you give me advice?

1. Are these capacitors (C5,C6) for AC coupling (User guide P14)?

2. From public "Serial-GMII Specification", receive input voltage range is 675mV-1725mV.
    They think is it difficult to meet receive input voltage range, if there are AC coupling capacitors.
    Is it correct?

I'm not familiar with high speed signal line, so I would appreciate if you would give me advice.

Thanks and best regards,
Ryo Akashi  
  • Hello,

    Regarding your questions:

    1) Yes, these are AC coupling capacitors.

    2) The PHY only cares about the differential voltage, so as long as that spec is met (see table 2 of the document), this should be fine. The PHY itself would take care of the DC biasing.