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CC2640R2F: Schematic and layout revision

Giacomo Zanichelli
Intellectual 445 points

Part Number: CC2640R2F

Hi all,

I've almost completed my design using CC2640R2F 48 pins device. I would very much appreciate a review of both the schematic and Gerber files to make sure everything is correct before fabrication.

A few details:

  • minimum trace width 0.110 mm (but at least 0.200 mm for power and RF)
  • minimum trace isolation distance 0.110 mm
  • 2 layer board
  • FR4 material
  • board thickness 1.55 mm
  • copper thickness 12 um
  • external regulator mode, with voltage regulator for digital components and separated reference for analog circuit

I did not match the impedance of the RF path but I've been very careful to minimize the trace length. I used 0.5 mm because that's the width of the antenna (AN043) at the feed point.

Thanks you for your time.

Best regards,

Jack

EDIT:

I was unable to post the drill files because .drl are not an accepted file format. How can I post it? To be precise, I've not been able to export any different format for the drill files from Cadence Allegro.

3060.BOTL.art6237.TOPL.art1586.SOLDERMASKB.art8838.SOLDERMASKT.artbiowatch_rev_1_1.pdf

  • 0
    TI__Genius 14930 points
    Jack,

    I will go ahead and take a look at your design and get back to you with comments and concerns.

    Best regards,

    Matt
  • 0
    TI__Genius 14930 points
    Jack,

    Here are some comments on the schematic:

    - The loading capacitors on the low frequency crystal seem to be higher than recommend by the CC2640R2F Launchpad reference design and the datasheet of the crystal you are using

    - The single ended antenna looks good, just be sure to leave a non-populated component pad for a passive component to allow for impedance matching


    Could you please provide all of the gerber files for your design (such as the silkscreen) so that I can properly analyze your layout? I should be fine without the drill files.

    Best regards,

    Matt
  • 0 in reply to Matt Calvo
    Intellectual 445 points

    Hi Matt,

    thanks for your answer.

    - I believe I copy pasted the loading capacitors of the low frequency crystal from the close DCOUPL pin bypass capacitor. I corrected it in the schematic.

    - I'm not familiar with impedance matching circuits. Are you suggesting to leave space for a passive to be inserted by trial and error during testing? Which footprint would you recommend? How sould I proceed to decide which value I should pick?

    - I used class 1 capacitors for low frequency crystal and RF front end. Can you confirm my choice? I included in the updated schematic the code of each capacitor

    It's actually easier for me to upload Cadence Allegro design file (.brd). let me know if you have troubles opening it. On the silkscreen layer I removed the passive components for lack of space so I don't thing would be very useful.

    Best regards,

    Jackbiowatch_rev_4_1.pdfBiowatch_4_1.brd

  • 0 in reply to Giacomo Zanichelli
    Intellectual 445 points
    Hi Matt,
    I have one further question: would you advice against placing silkscreen on bottom, below the antenna? That's the only space I have to put my name and revision code.

    Best regards,
    Jack
  • 0 in reply to Giacomo Zanichelli
    TI__Genius 14930 points
    Jack,

    - Please refer to the CC2640R2F Launchpad schematic for reference. The impedance matching component (C15) is a "non populated" component on the schematic. It provides space for an inductor or capacitor to be placed there, after performing impedance matching testing. The idea behind impedance matching is to make the antenna look like an impedance of 50 Ohms so that it pairs with the rest of the circuit. The value of inductor or capacitor to pick is determined using a network analyzer to measure the impedance of the antenna, on its own, and then a Smith Chart tool is used to determine what value component can be placed in parallel with the antenna to change its impedance to 50 Ohms. There should be information online about it; and if I can find a good resource for impedance matching then I will go ahead and share it with you

    - As long as the capacitors are the correct values and can withstand the voltages applied to them, then you should be fine.

    - I do not have Cadence so I can't open the Allegro file at this moment; however I do have Altium. I wanted to see the silkscreen to make sure that the passive components that are supposed to be placed near respective pins are in fact placed and routed near their associated pin. You can confirm this yourself since you've labeled on the schematic where the filtering components are supposed to be placed.

    - Since our Launchpads have silkscreen labels on the antenna portion of the board, I think you should be fine!

    Best regards,

    Matt Calvo
  • 0 in reply to Giacomo Zanichelli
    TI__Genius 14930 points

    Jack,

    Attached you'll find a slide set that explains antenna theory and matching!

    -Matt

    AntennaBasicsMatching.pptx

  • 0 in reply to Matt Calvo
    Intellectual 445 points

    Hi Matt,

    Thanks for your detailed answer.

    I don't have a network analyzer to measure the impedence so I think I would risk it without placing the non populated component.

    I'll go ahead with fabrication and let you know the results.

    Best regards,

    Jack