We are planning to use the TMUXHS4212 as a mux on a PCIe Gen3 link (8Gbps). The one part of the link is connected as follows:
The AC coupled Tx of a NVMe SSD module is connected to the input of the TMUXHS4212, and the output of the TMUXHS4212 is connected to the input of a PCIe ReDriver. The PCIe ReDriver has a common mode voltage of about 3.2V so this will probably not work due to the 0-1.8V common voltage input range of the TMUXHS4212.
The plan is to add AC coupling capacitors between the TMUXHS4212 and the PCIe ReDriver inputs.
My question is regarding the value of the AC coupling capacitors between the TMUXHS4212 and the ReDriver. According to the PCIe Gen3 specification, AC coupling capacitors should be in the range from 176nF to 265nF, which probably also is the value of the AC coupling capacitor on Tx of the NVMe SSD. By adding an AC coupling capacitor between the TMUXHS4212 and the ReDriver, this capacitor will be in series with the capacitor on the SSD module even though there are a few centimetres of PCB track and a TMUXHS4212 in-between.
What value would you recommend for the AC coupling capacitor between the TMUXHS4212 and the ReDriver?
