For RJ45 with built-in pulse transformer,
How should I place the GND plane for differential signals?
Please let me know if there is a recommended layout.
If the GND plane is placed close to the differential signal pins of the RJ45,
the GND plane will be strongly affected by electrostatic discharge.
On the other hand, if the GND plane is placed outside the RJ45, it will affect impedance control.
Which should I prioritize?
Hi Taka,
snlr048.zip (layout checklist for DP83867)
Are you referring to the placement of the GND plane on the same layer, or the orientation of the PCB layer stack?
We recommend this 30mil spacing between the ground plane and high-speed traces, and a similar spacing to the RJ-45 connector. If there is a solid ground plane reference on another layer, then the impedance control does not appear to be a significant concern compared to cross-talk to the high-speed signals.
Thank you,
Evan
Hi Evan,
>Are you referring to the placement of the GND plane on the same layer, or the orientation of the PCB layer stack?
I'm referring to the PCB layer stack.
The figure below shows the wiring pattern near the RJ45 pins.
Layer 1 is the differential signal, layer 2 is the GND plane.
This layout has a GND plane under the RJ45 for impedance control.
However, since this layout is affected by electrostatic discharge,
I think it is better to extend the GND plane to the outside of RJ45. Is this correct?
