PCIe AC coupling of the MCIMX6DL-SDP

[torus1000]

Hi,

I created this thread for separating new questions from original one. igorpadykov‌
https://community.nxp.com/message/987667

My questions about PCIe of MCIMX6DL-SDP are as following.
Please refer to the circuit diagram SPF-27417_C4.pdf on page 16.

According to the PCIe standard, All Transmitters shall be AC coupled.

PCIe AC coupling capacitors values
https://community.nxp.com/thread/463277
http://composter.com.ua/documents/PCI_Express_Base_Specification_Revision_3.0.pdf p357

(Q) Why 0 ohm resister placed at C7 and C8 instead of capacitor.

I think REFCLKM/P need no capacitors but there was differntial termination and AC coupled.

(Q) Why reference clocks also AC coupled?

Can anyone help me?

[igorpadykov · Accepted solution]

Hi torus1000

>(Q) Why 0 ohm resister placed at C7 and C8 instead of capacitor.

C7,8 are i.MX PCIe receiver side, no capacitors are needed as you correctly noted that

according to the PCIe standard,  all transmitters shall be AC coupled.

So capacitors are installed on PCIe card side acting as transmitter.

>(Q) Why reference clocks also AC coupled?

i.MX reference clocks are transmitter side, so as you correctly noted that

according to the PCIe standard,  all transmitters shall be AC coupled.

Best regards
igor
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