Other Parts Discussed in Thread: TMUXHS4412, DS160PR421
we chose the part TMUXHS4212 as passive mux/demux in order to share/switch 4 PCIe x4 Gen.4 lanes (4 Tx and 4 RX channels) between two slots. The PCIe Root Complex comes from an host GPU.
The switch via SEL pin is hard wired via PUR/PUD resistors straps so the bus direction torwards the slot are static.
Major doubts comes from placement options of coupling capacitors and corresponding need of bias resistors host side on tx and Rx lanes, according to options of fig. 8.1 of the datasheet.
Please find attached the related schematic page where you can locate the two TMUXHS4412, one for RX lanes (U41 as a Mux) and one to Tx lanes (U42 acts as Demux). Tx caps are place on connector side.
Path A of the muxes addresses the M.2 Key M slot you can see on the sheet, whilst muxes path B address a similar expansion connector, not here represented.
Questions are:
- For U41 TMUXHS4412 Mux, can the highlighted ac caps be replaced with 0R resitors or even eliminated?
- In case we want to use the DS160PR421 redriver option for signal integrity issues are those caps necessary?
- Do we have to foresee any bias resistors on host side on rx path, like proposed on fig. 8.1c of the datasheet?
