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LMH0302: Layout Example: Board/PCB ground same as Chassis ground?

Part Number: LMH0302

My customer is using the LMH0302 to drive a 3G-SDI signal to a BNC connector that mates directly the the chassis. Therefore, the BNC connector is mated to the Chassis ground.

In Figure6 (p.11) - "Layout Example" in the LMH0302 datasheet, it is not clear if the ground of the "BNC Anti-pad" is connected to the Board/PCB ground, or if this is the Chassis ground.

Please help with the following questions:

1. Is the light green ground section on the "Layout Example" the Board/PCB Ground? The Chassis Ground? Or both (ie, PCB and Chassis ground are tied together)?

2. Should the diagram show gold solder connections above and below the BNC Anti-Pad such that the BNC connector is connected to the light green GND?

3. In this case, since the BNC connector mates directly to the chassis, is it recommended to tie the chassis ground directly to board ground? Or are there any other recommendations (typically one would want to filter out chassis noise with ferrite bead + inductor)?

Thanks!

Andy

  • Hi Andy,

    Please note comments below:

    1). Light green area is the board/BNC ground.

    2). First of all, we should make sure to use BNC supplier anti-pad recommendation. Secondly area above BNC anti pad could be gold solder but as long as it is about 5 times 75-ohm trace width - to make sure it does not interfere with trace impedance.  

    3). Mating chassis gnd to board ground is a system question and maybe this depends on the overall system EMI. Perhaps to reduce EMI it could be a good idea to have a place holder for a ferrite bead or an inductor.

    Regards,,nasser

  • Hi Nasser,
    Thank you for your feedback. This clarified these items for the customer. Appreciate the quick response!
    Regards,
    Andy