DFE IQ sampling and antenna switching slots confusion

RE: DFE IQ sampling and antenna switching slots confusion

Pete W — Thu, 19 Dec 2019 15:48:48 GMT

Yes, I thought that RADIO_DFECTRL1_TSWITCHSPACING_xxx and RADIO_DFECTRL1_TSAMPLESPACING_xxx were the slot lengths, but clearly not. I'm not intending to use BLE so will just discard the samples that I know fall close to the switch transitions.

RE: DFE IQ sampling and antenna switching slots confusion

Dmitry — Wed, 18 Dec 2019 13:22:18 GMT

I agree, there's some inconsistency between spec and implementation - "Interval between samples" is not the same as "sample slot length". IMHO a "switching slot" just means that we should not use IQ data during transition period, but we can take them though, as nFR52811 does.

RE: DFE IQ sampling and antenna switching slots confusion

Pete W — Wed, 18 Dec 2019 13:08:22 GMT

Hi Dmitry,

What I meant was that if the antenna switch slots are 2us long, and the sampling slots are also 2us long and fall between the switching slots, as per 5.1 core spec (fig below), then that suggests that sampling is only valid for 2us every 4us, otherwise what is the point of 'switching slots'? It also suggests that only 1 antenna change should occur in each switching slot. It would all be so much easier if the spec just said "switch at rate X, sample at rate Y. Avoid sampling within Z ns of switchover".

Pete

RE: DFE IQ sampling and antenna switching slots confusion

Pete W — Wed, 18 Dec 2019 12:48:43 GMT

Hi Bjørn,

Thanks for the reply.

I should've added that I have CTEINLINECTRLEN set to 0. I hadn't investigated what happens in CTE inline enabled mode as I wasn't intending to use it that way (I thought I'd be stuck with 1 or 2 us timings). I am using AoA mode and I have TSWITCHSPACING set to 2us and TSAMPLESPACING set to 125ns, as I want to oversample for now. I currently don't do any antenna switching, but I am monitoring the control pins to see when they change. I see a continuous sinusoids in my IQ samples (at least after a 1us jump following the reference) so samples are being taken all the time, i.e. through the switching slots.

I'm really struggling with the switching slots. Is the antenna switch-over coincident with the centre of the switching slot, so that the slot's purpose is to allow for slow edges, or is there a switchover at the slot boundaries (as I seem to be seeing)?

If I enable CTE inline mode, and keep TSWITCHSPACING at 2us, then it seems that the sample timing will use CTEINLINERXMODE1US, and the default for that is 2us (CTEINLINECONF FFF=010). But the slots alternate! I keep going round in circles with this - nothing seems to add up for me.

Regards

Pete

RE: DFE IQ sampling and antenna switching slots confusion

Dmitry — Wed, 18 Dec 2019 12:35:42 GMT

Hi Pete,

[quote userid="79956" url="~/f/nordic-q-a/55626/dfe-iq-sampling-and-antenna-switching-slots-confusion"]but when I select '2us spacing' the lines toggle every 2us. [/quote]

That's right, 1us/1us sample/switch.

[quote userid="79956" url="~/f/nordic-q-a/55626/dfe-iq-sampling-and-antenna-switching-slots-confusion"]the 2us sample slots - which apparently are 4us apart[/quote]

A bit confused... with 2us sample slot settings, you will get a sample every 2us.

RE: DFE IQ sampling and antenna switching slots confusion

bjorn-spockeli — Wed, 18 Dec 2019 10:24:57 GMT

Hi Peter,

Is CTEINLINECONF.CTEINLINECTRLEN set or not?

Also what is the TSWITCHSPACING and the TSAMPLESPACING set to in the DFECTRL1 register? It is by default set to 2us and 4us respectivly.

Best regards

Bjørn