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I recently noticed that the U.3 SFF-TA-1001 AC coupling capacitor requirement is very different than what I have known in other specs like SATA, PCIe, and USB3.0.

SFF-TA-1001 requires 2.2uF at each device RX. Furthermore, of the four lanes, two TX lanes do not require an AC coupling capacitor but the other two do. Does anyone know what the purpose of doing this is? This is killing me.

Within the document "SFF-TA-1001 r1.1.PDF", the requirement is listed on page 18.

JYelton
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Zac Chien
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    link to the specifications, and indicate section / page / table / figure numbers where this puzzling requirement can be found – Neil_UK Aug 19 '21 at 07:47
  • Does [this](https://electronics.stackexchange.com/questions/514711/why-are-pcies-coupling-capacitors-so-large?rq=1) question answer offer a hint at the reason? Note the OP in that question did indicate a source for their confusing requirement. – Neil_UK Aug 19 '21 at 07:50
  • Hello, you can search the document “SFF-TA-1001 r1.1.PDF” and the requirement listed in page 18. No reason explained… – Zac Chien Aug 19 '21 at 07:57
  • Is this the correct link to your document? https://members.snia.org/document/dl/26900 – JYelton Aug 19 '21 at 15:20
  • Yes correct. Thanks. – Zac Chien Aug 20 '21 at 06:54
  • For SDI, AC-coupling capacitors value is 4.7uF due to the data pattern (duration of maximum continuous one or zero), the RC time constant need to be adjusted to data pattern. So maybe with the different protocols SFF decided that 2.2uF was a good value that would match all possible data patterns. – zeqL Dec 01 '21 at 22:27

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