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Are the 0.1 μF capacitors in the schematic I found on the internet for the USB hub USB5537B connected to all the TXs required? What is their purpose?

Normally I know that series capacitors are used to block DC signals. Is there a need to block DC signals here?

enter image description here

Source: https://www.microchip.com/forums/download.axd?file=1;1046830

JRE
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George P.
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  • Please supply data sheet links to the chief parts and read them first to understand what IO pins the 100 nF capacitors are connected to. – Andy aka Jul 18 '22 at 12:55

2 Answers2

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They are not there just to block the DC, but also meet the impedance requirements. You want the diff pairs between the transmitter and the receiver to be coupled properly.

RX lines don't have the AC coupling capacitors because the transmitter on the other side (i.e. another connected device) must already have those. I can't say if placing the coupling caps closer to the transmitter is the best practice but that is how it's done. For more info about AC coupling caps on high speed / high frequency circuits take a look at here.

Rohat Kılıç
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7

USB3 signals are AC coupled so the DC needs to be removed with capacitors.

Justme
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    Note that DC offsets can arise between devices because of ground differences, in addition to circuit particulars. While differential interfaces help in this regard, they can break down (figuratively) if offsets exceed the common mode range of the receivers. – SteveSh Jul 18 '22 at 13:43