[FAQ] Do PCIe redrivers support polarity inversion of differential channels?

Inherently, PCIe redrivers are not protocol aware. So, they would not be able to determine "positive" and "negative" input and thus they are not sensitive to polarity inversion on their differential channels when used in PCIe applications.

Per PCIe specification, polarity inversion is done on the protocol layer. PCIe NRZ data is polarity insensitive. For ease of schematic/layout design, this means you can connect the negative terminal of a PCIe redriver to the positive terminal of the device (or vice versa) after AC coupling. Then, the PCIe protocol will adjust accordingly during the Training Sequence Ordered Sets (TS1 and TS2). Note that the polarity inversion is always handled by the PCIe receiver (root complex and/or endpoint), never the transmitter. All PCIe lanes support independent polarity inversion.

Please note that when PCIe redrivers are used in non-PCIe applications, polarity inversion is dependent upon the protocol with which the device is used. Care should be taken to ensure that if polarity inversion if desired in a non-PCIe application, the protocol supports this design. 

Best,
David