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DS125BR800: Cascade AC coupling capacitor

Ogoshi Tomoki
Prodigy 30 points
Part Number: DS125BR800

Tool/software:

Hi,

Using the DS125BR800 for 10Gbps PCIe communication with a differential impedance of 100Ω (50Ω single-ended),

please specify the recommended AC coupling capacitor values for both the Tx and Rx sides of the DS125BR800.

Additionally, due to system constraints,

it is necessary to connect two AC coupling capacitors in series on the Tx side.

• One of the capacitors is located on the module and is fixed at 100nF. What should the value of the other capacitor be?

• I would also like to know whether DC bias is required in the section between the capacitors.

  • 0
    TI__Mastermind 36793 points

    Hi Tomoki-san,

    Checking with a colleague and will get back to you shortly.

    A few questions:

    • Can you add more details regarding "10Gbps PCIe communication"?  I'm familiar with 8 Gbps PCIe and 16 Gbps PCIe, but not 10 Gbps.  Is this for SLVS-EC?
    • Regarding "it is necessary to connect two AC coupling capacitors in series on the Tx side.", is this a strict requirement?  If RX module already has AC coupling, I'm wondering if AC coupling after DS125BR800 can be removed.

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    Prodigy 30 points

    Hi,

    Thank you for your reply.

    • Can you add more details regarding "10Gbps PCIe communication"?  I'm familiar with 8 Gbps PCIe and 16 Gbps PCIe, but not 10 Gbps.  Is this for SLVS-EC?
      ->Yes. I mean SLVS-EC(9.2Gbps)
    • Regarding "it is necessary to connect two AC coupling capacitors in series on the Tx side.", is this a strict requirement?  If RX module already has AC coupling, I'm wondering if AC coupling after DS125BR800 can be removed.
      ->It's strict requirement. We cannot avoid this requiment..
  • +1 in reply to Ogoshi Tomoki
    TI__Mastermind 36793 points

    Hi Tomoki-san,

    • DC bias is not required between the capacitors
    • I'd consider 100nF or 220nF.  220nF will help keep higher total capacitance.

    Thanks,

    Drew