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CC2541 Balun and antenna design - Design check

Spandan89
Expert 1420 points
Other Parts Discussed in Thread: CC2541

Hi,

I am using CC2541 + Balun 2450BM15A0002 + MIFA antenna. I'm following antenna dimensions mentioned in swra117d. I'm also following recommended balun design from manudacturer. I'm considering following design things mentioned by TI and other manufacturers in general.

- Solid ground plane underneath CC2541 antenna pins and balun.

- No solid copper region underneath pcb antenna on any layer. I'm using 4 layer design as mentioned in CC2541 Keyfob's Read me file. should there be GND plane below pcb antenna?

- placed lots of vias spaced apart 1.25mm near antenna section.

- Top and Bottom layer are filled with copper pour. Both connected using lots of vias.

- Both crystal and decoupling capacitors are placed as closely as possible.

Questions:

- PCB Antenna's feed line is connected to Balun's antenna pin and pcb antenna's other part is connected to GND. How do I mention this in Altium. Its giving me error. I used solid fill region to make pcb antenna, is it right tool to use?

- Via near antenna section, should these be drilled to GND plane underneath the RF section or should these via be connected to Copper pour on Bottom layer?

  • 0
    TI__Mastermind 36375 points

    Spandan89,

    Answers inline:

    Solid ground plane underneath CC2541 antenna pins and balun.

    • Good

    - No solid copper region underneath pcb antenna on any layer. I'm using 4 layer design as mentioned in CC2541 Keyfob's Read me file. should there be GND plane below pcb antenna?

    • Good

    - placed lots of vias spaced apart 1.25mm near antenna section.

    • Those via look like they are not connected to the ground planes, they need to be. Also place some on the bottom of the PCB near the ground connection of the antenna.

    - Top and Bottom layer are filled with copper pour. Both connected using lots of vias.

    • I cannot see the via placements inside your ground pour areas, could you repost with vias visible somehow.

    - Both crystal and decoupling capacitors are placed as closely as possible.

    • Good

    Questions:

    - PCB Antenna's feed line is connected to Balun's antenna pin and pcb antenna's other part is connected to GND. How do I mention this in Altium. Its giving me error. I used solid fill region to make pcb antenna, is it right tool to use?

    • Sorry, I am not a tools expert, but this is a common issue with tools and antenna structures.

    - Via near antenna section, should these be drilled to GND plane underneath the RF section or should these via be connected to Copper pour on Bottom layer?

    • I recommend ground connected vias that connect as many gnd layers together as possible. 

    Regards,
    /TA

  • 0 in reply to TA12012
    Expert 1420 points

    Hi,

    Really appreciate your quick reply.

    Here is updated pcb layout.

    I have defined polygon pour cutout area on TOP, GND plane, POWER Plane. I havent defined cutout area on BOTTOM layer. You can see blue area underneath CC2541 pins and balun. is that okay? should I define cutout region there too?

    I have defined those via (near ANTENNA section) from TOP to GND plane.

    I have added via stitching (top left corner). these via connect TOP and BOTTOM copper pour.

    TOP and BOTTOM Layout

    TOP Layout

    BOTTOM Layout

    GND Plane

    POWER Plane

    One more thing, I havent added pi netowork for antenna tuning.  I have made sure that there is a 50 ohm tace from balun to antenna's feed point. is it good practice to add antenna tuning network? Any other suggestions are welcome.

    Thanks again.

  • 0 in reply to Spandan89
    TI__Mastermind 36375 points

    You need to add more via to your design, for every decoupling capacitor you add to your design you should have 2-3 ground vias. See my suggestion below.

    I need to look into the ground plane question a little.

    Regards,
    /TA

      

  • 0 in reply to TA12012
    Expert 1420 points
    Hi,

    Got your point. I'll add more vias and connect those to GND plane.
  • 0 in reply to TA12012
    Expert 1420 points
    Hey,

    Did you get a chance to look into GND plane?
  • 0 in reply to Spandan89
    Expert 1420 points

    I have continued this thread here with updated design.