Even though I’m a Decawave person, I wasn’t involved in the design of the modules or the DW1000. I will try to discuss this with someone who knows a bit more.
The “best” arrangement of decoupling components depends on the use and how you think about it. You could consider the decoupling caps and the FB having 3 main functions:
- Preventing voltage drops at the pin and thus ensuring the PA always has sufficient current for a correct operation
- Preventing transient currents from propagating to the power supply, important to keep the supply regulators stable
- Preventing radio signals from propagating on the supply line, preventing unintended radiated emissions from the supply rails.
Optimizing for point 1 means FB -> 47uF cap -> smaller caps -> pin like option 3-4 will work best since the big decoupling cap will allow the pin to draw big transient currents without being choked by the FB.
For point 2 and 3 the 47uF cap -> FB -> smaller caps -> pin would work better since the FB will typically be better at blocking the high frequency noise / transients, effectively forming a pi filter.
To be honest. looking at the datasheet of the FB used, I don’t think the filtering of the modules is optimal, since it is designed to block EMI noise at 100-1000MHz.
The DW1000 IC supports UWB channels 1-5 and 7, ergo a frequency of 3244.8-6998.9 MHz. At these frequencies the FBs won’t block a lot. It could be though that the designer is filtering lower frequency noise I’m not aware of. Either way, all modules passed EMI verification, so the EMI is blocked sufficiently to meet regulations.
The optimal decoupling cap values depend on the used frequency, and thus on the used UWB band. Note that the DW1004 was mainly designed for TDoA applications, requiring mainly TX operation from the tags. This could explain the difference in decoupling caps, but as Andy mentioned, the effect will be minimal. It could also be the 12pF caps where found to work better empirically, but I was not able to find anything on this.
TL;DR: the module designs pass EMI regulations (at least in band 2 and 5 as far as I am aware) and work as intended, your mileage may vary since a lot depends on the PCB layout, size and even stackup and component sizes, as well as the used bands, but if you follow the suggestions in the datasheet you should be fine.
Seppe