Problem with PN7150 NFC Antenna Simulation using RFSim99

[Franz75]

Hello,

I read some app. Note for RFID matching and I've followed NFC Antenna Design training in particular part 2.

But my theoretical simulation with RFSim99 doesn't look like what I read on the instrument, I certainly did something wrong, but what?

My steps are:
First I calibrate the VNA with a coaxial cable.

I measure the parameters and resonance frequency of the antenna directly on the dump resistors.

The parameters read by the VNA are:

L = 1.68uH

R = 6.74Ω

Ca= 1/ ((2*3.14*55.345E6)^2*1.68e-6=4.92pF

The simulation:

But I measured:

What am I doing wrong?

thanks in advance.

Francesco

[Tomas_Parizek · Accepted solution]

Hello Francesco, 

I tried to simulate your circuit and I can see approx. the same:

btw. I always put something like 1.25Ohms in front of the inductors which simulate the inductors and connection losses. 

About your topic, I see the resistance of your antenna is 6.72 Ohms. That is quite a lot. Do you really measure the antenna itself? Or did you include the damping resistors as well? 

Once I decreased the Rs of the antenna, the results were more realistic 

BR

Tomas 

[Franz75]

Hi Tomas,
the rs value was actually very high and as you can see from the photograph the dump resistors were not present. but by doing the same things again with the same "instrument" I now read 3 ohm... most likely the small VNA is of poor quality. Now everything works.
Thank you very much

[Franz75]

Danielchen thank you for your response,
but maybe I explained myself wrong.
The actual circuit was made as NXP specification with ground connected on C0 and C2, but in the simulation the ground is connected only on TX2.
I ran the simulation on the PC then to redo it in practice with the VNA I reproduced just simulated.
My DUT is connected between TX1 and TX2 and capacitors C0 and C2 are NOT at GND and the GND trace was cut to everything else in the circuit.
I look forward to hearing from you.
Thank you

Francesco

.

[danielchen]

Hi

There is a difference between the real circuit and the simulation,  I would suggest you refer to below link for RFSim99 

https://community.nxp.com/t5/NFC/PN7150-NFC-Antenna-Simulation-using-RFSim99-Simulation-Tool/td-p/14...