PCIe_x8_Breakout

PCIe x8 Signal Breakout to U.FL/UMCC Connectors.

PCIEX1-SMA is a similar project that is PCIe x1 and uses SMA connectors.

The board requires up to 34 U.FL/UMCC Surface Mount Receptacles and a 16-Pin 2.54mm Header or Socket.

Related Projects: OpenCAPI_Breakout, OpenCAPI-to-PCIe, OpenCAPI-to-PCIe_x4_Host_and_Endpoint

Testing and Use Example

The board is currently being used along with an OpenCAPI_Breakout board to test OpenCAPI-to-PCIe on the Innova-2 SmartNIC. PCIe 3.0 x4 at 8.0GT/s is currently working. Standard 0.1" M-F Jumpers are used for the PCIe Reset Signal (nPERST) and its GND.

With cables shorter than 4"~=100mm the adapters work. Note the RX U.FL-to-U.FL cables are all the same length as each other and likewise all TX cables are the same length but RX and TX are different lengths as that is what I had access to. RX on the PCIe board connects to RX on the OpenCAPI board as it uses the OpenCAPI Host pinout.

PCIe x4 In-system:

However, using 250mm IPEX cables the adapters fail for PCIe x8:

PCIe x8 In-system:

PCB Layout

All signals are length-matched to within 1mm both inter-pair and intra-pair.

Resistor footprint R1 connects PRSNT1 to PRSNT2_x8. The R1 trace can be cut and PRSNT1 can be connected to a different PRSNT2 to reduce the PCIe lane width.

Wire jumpers can then be used to connect PRSNT1 to any of the PRSNT2.

Schematic

PCB Layer Stackup

4-Layer PCB stackup taken from JLCPCB.

Differential Impedance parameters were calculated using the DigiKey Online Calculator.