Hi,
I have been wondering about if these Sintech NGFF (or other brands) adapters are designed completely using the correct LVDS guidelines?
Each PCIe lane is actually a LVDS interface consisting of two unidirectional differential pairs that should be designed using LVDS design rules:
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- LVDS utilizes a differential transmission scheme, which means that every LVDS signal uses two lines. The voltage difference between these two lines defines the value of the LVDS signal. For successful transmission of LVDS signals over differential traces, the following guidelines should be followed while laying out the board.
- To ensure minimal reflections and maintain the receiver’s common mode noise rejection, run the differential traces as closely as possible after they leave the driving IC. Also, to avoid discontinuities in the differential impedance, the distance between the differential LVDS signals should remain constant over the entire length of the traces.
- To minimize skew, the electrical lengths between the differential LVDS traces should be the same. Arrival of one of the signals before the other creates a phase difference between the signal pair, which impairs the system performance by reducing the available receiver skew margin (RSKM).
- Minimize the number of vias or other discontinuities on the signal path.
- Any parasitic loading, such as capacitance, must be present in equal amounts to each line of the differential pair.
- To avoid signal discontinuities, arcs or 45traces are recommended instead of 90turns.
Source:
https://www.altera.com/en_US/pdfs/literature/wp/wp_lvdsboard.pdf
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Are these "China" boards properly designed?
Is it maybe skew in the differental lines that are causing problems for us?
BR Flemming Dahlhof Jensen