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New vs old ref-design for QFAA/AB and QFAC with discrete balun

andlier

In my current design, for the schematic and layout I've copied the design of the first version of the usb-stick with meander-antenna and matching network/balun. In the later designs of this board (for later revision of the chip I assume) I notice that Nordic has changed the discrete balun to be identical to the reference designs in the PS-document. (notable changes: instead of 3 identical 6.8nH inductors, they now have 3 different inductors 10nH, 4.7nH and 3.3nH for the QFAA/QFAB (16k ram), and 27nH, 4.7nH, 3.3nH for the QFAC (32k ram). )

Questions:

1: What are the reason for these changes in the matching network?

2: Can I just stick with my schematic/design from the PCA10000 v1.0.3 even if I upgrade to latest chip-revision of QFAA or AB? or is it advisable to update the design? Would I get better performance in any way if moving over to the latest design?

3: Is it because of different silicon-die that the QFAC has different component values? (I can't move between 16k and 32k ram without also changing component values?)

  • 0

    Replying because I am interested in this too. Can QFAC be "dropped in" to a mature QFAA design and expected to work?

  • FormerMember
    0 FormerMember
    1. The matching network* for QFAA/AB (16 kB RAM) hasn't changed between silicon revision 2 and 3. And silicon revision 3 is therefore drop-in compatible with silicon revision 2 for QFAA/AB. The QFAC (32 kB RAM) is, as you probably already know, a little larger than the QFAA/AB, and the output is slightly different; a 27 nH inductor has to be used in the matching network instead of the 10 nH inductor. It means that QFAC device is not drop-in compatible with any of the QFAA versions.
    2. The values that you use in the matching network* should correspond to the values in the reference layout for your chip variant. The purpose of the matching network is explained in the blog post "General PCB design guidelines for nRF51" -> Matching networks -> Matching the chip to 50 Ohm.
    3. See 1.

    *Matching network: in this answer, "matching network" refers to the matching network for matching the chip to 50 Ohm.

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