This is part one of a two-part video series on near-field communication testing using
an InfiniiVision X-Series oscilloscope.
This particular video will focus primarily on using the scope’s built-in NFC triggering,
and then performing various parametric measurements using some of the scope’s built-in math
functions and automated parametric measurement capability.
Now, part two video focuses on automated testing using an external app on a PC along with various
other pieces of equipment.
So I encourage you to watch that one after you watch this one.
So let’s go ahead and get started with this one.
What I’m going to be testing is communication between a tag, which happens to be NFC-A,
and a mobile phone, which supports multiple Poller and Listener modes.
The way I’m going to capture these signals is I have a NFC calibration coil here.
You could think of it as a sniffer, RF sniffer, or an RF probe.
What I’m going to do first is simply place my NFC tag onto this calibration coil antenna.
And then I have a very precision spacer here, a yellow sticky pad.
It’s about five millimeters.
I ripped it in half.
And then I’m going to place my mobile phone onto that.
Now, if you heard the doink, first of all, that’s a good sign; they’re communicating.
Now, that’s as far as some people go when it comes to testing NFC.
But I think you should go a little further than that.
So let’s go ahead and take a look at these signals, look at the quality of them, and
make various measurements on the oscilloscope.
We’ll begin with a default setup, and then we’ll set up everything from scratch.
Let’s go into the channel one menu first of all and select 50Ω coupling.
And now let’s scale the vertical; get close to full-scale scaling here.
And now let’s go into the trigger menu.
The default trigger is edge triggering.
Now, what a lot of people use for triggering on NFC is pulse width triggering.
But it’s very difficult to lock in on specific sense requests or responses.
So in this oscilloscope with the NFC option, we have NFC triggering.
So that’s what we’ll select.
Now it’s got a very low trigger rep rate, so we need to go to the normal trigger as
opposed to auto.
And let me turn up the waveform intensity here.
And we can probably see something here.
This is either the sense request or all-request coming from the mobile phone, which is the
Poller in this case.
And this may be difficult to see.
This is the response from the tag that I’m testing.
Now, if I scale down a little bit here, you can also see, later on during the communication
the SDD request, or single-device detection request, and then the SDD response again from
the tag.
So let’s go back, zoom back in on this first set of communications with the sense request
or the all-request and the response.
And let’s take a look at the various trigger selections.
You can trigger on NFC-A, B, NFC-F212, or 424.
The default, when I press Default Setup, goes to NFC-A. And then you can also trigger on
specific events: sense request, which – this tells me it stopped triggering.
It’s not a sense request.
It is an all-request.
Or I could select either, which was the default.
And then you can also trigger on SDD request.
We’ll use that one later on.
So let’s go to trigger on all-request.
The next thing: let’s perform some measurements on both signals from the Listener – being
the NFC tag, that’s this right here.
And then we’ll perform some Poller testing.
The first thing we might want to know is the frame delay time.
For that, I could use some automated measurements and set up custom thresholds.
But the easiest is just to use the cursors.
And we’ll put my X1 marker there and my X2 marker at the beginning of the responses.
And I can read off delta-X: 92 µs.
That’s within the limits.
Off the top of the head, I don’t know what the exact limits are.
You can check in the NFC specification.
Next, let’s zoom in on just the response and look at some of these bits out here.
I’m going to use the scope’s zoom mode.
I’m going to turn the cursors back off.
Let’s open it up a little bit, scroll over here.
And here we can see the response modulation.
What I’d like to do now is set up the waveform math function in the oscilloscope to demodulate
it for us in software.
So I’m going to select the waveform math function, Math 1.
And I’m going to use a math function called Envelope mode, which runs a Hilbert transform
on channel one.
Well, I turned it off.
Let’s turn it back on.
Now, this looks pretty noisy.
Now, we can add to this a smoothing filter on Math 1.
And let’s do about a seven-point smoothing filter.
So there’s our load modulation.
Now, at this point, I can perform some measurements specifically on this demodulated waveform.
For instance, if you wanted to know what the load modulation amplitude is, I could select
Measurements, add a measurement on Math2, and select Amplitude.
And it’s about 72 mV.
If I want to know what the frequency is – this is the subcarrier.
Let’s just measure the frequency on Math 2.
And it should be about 845 kHz.
Now there’s another way you can make measurements on the subcarrier, this modulation.
That’s in the frequency domain.
Let’s set that up now.
So I’m going to turn off this math function and turn on FFT.
I’m going to perform an FFT magnitude on channel one, but it’s going to be a gated
FFT by the zoom mode.
I only want to perform the FFT on this subcarrier within the modulation.
So first of all I need to zoom in a little further.
Must go back and set up a center frequency of 13.56 MHz and a span of about 3 MHz.
And so here, we can see the carrier.
This is the lower sideband and the upper sideband.
Let’s use the scope’s frequency peak search capability.
Let’s search on three peaks.
Let’s set our thresholds down here so they’re within the sidebands.
And there you could see the triangles.
It has found these peaks.
And let’s put these in frequency order.
And here you can see these 13.52 MHz, 2.69 dBm; lower sideband 12.71 MHz.
And you can read the amplitude as well as the upper sideband.
Now, there’s not a lot of frequency resolution in this measurement.
Although what is most important is the amplitude of the sidebands.
If I want higher frequency resolution, I can open up my window and capture more cycles.
And you can see now it’s measuring 13.56 MHz.
So let’s move to make some measurements on the Poller signals now.
Let’s turn the FFT off.
Let’s go ahead and turn the zoom off.
And now I’m going to change the trigger to trigger on SDD request.
So this is the SDD request.
Let’s turn the zoom mode back on and scroll back over to this series of pulses.
These is the modulation that’s coming from my mobile phone.
Again, we will turn Math3 off, turn on Math2.
Should be all set up to show the demodulated waveform using software.
Now, the scaling is a little different.
I’m going to set that up so it is the same scaling.
Should be about 150 mV per division, same as channel one.
And offset should be about 0 V.
So that will lay it right on top of the modulation.
Now there’s a different set of parameters that you want to measure on NFC-A Poller signals.
They’re called T1, T2, T3, T4, and T5.
We’re going to do a couple of them here.
T2 is the time below the 5% level.
So we can use an automatic measurement for that.
We’re going to select a minus width measurement.
But I need to customize the thresholds on the Math2 waveform
and set the midpoint at 5%, then select that measurement.
So there you can see the time between the cursors is measuring approximately 2.1 µs.
Another critical measurement is: there’s two measurements that’re transition time
measurements.
So basically rise time measurements.
One is from 5% to 90%.
That’s the T3 factor.
And by the way, you probably saw on your screen a diagram showing these different timing parameters.
So let’s measure a rise time, and set the thresholds to measure from lower from 5%,
upper to 90%.
It’s already there.
Go back and add that measurement.
And there we measure about 460 ns.
And the other transition time measurement measures 5% to 60%.
And there you can see about 240 ns.
The last measurement I’ll make – it’s actually already up – is the frequency.
So this is the data rate.
It’s 106 kHz baud rate, 106 kbits per second.
If you’re a hardware designer working on NFC technology and you need to perform measurements
on your designs, I hope this video was beneficial for you to show you how to perform these various
measurements.
Some of the capabilities of this scope that made these measurements possible: number one,
probably the most important, is the ability to trigger on NFC signals, both NFC-A, B,
F212, and F424.
Although we only showed NFC-A. Other capabilities of this scope were the waveform math functions
in order to demodulate the waveform, as well as the gated FFT to do the sideband measurements.
If you’re interested in automated testing of NFC, I encourage you to watch the second
part of this video series.
If you want to see more information on NFC testing using oscilloscope, I encourage you
to go to the URL listed at the bottom of your screen.
Thanks for watching.