choosing an active probe for Rx NFC measurements

[maker8122]

Following NXP guidelines for selecting the right passive components between antenna and Rx pins of PN7462 NFC controller, they recommend using an Active probe with a low capacitance (<2-3pF) for taking voltage measurements at the pins during communication.

The cheapest active probe on Digikey looks to be: https://www.digikey.be/product-detail/en/cal-test-electronics/CT4066/CT4066-ND/9342238

Fair choice? Any recommendations?

 

[FvM]

Not very fast, just sufficient for 13.56 MHz. You should check if it's sensitive enough for your application, e.g. regarding noise level.

 

[maker8122]

Not very fast, just sufficient for 13.56 MHz. You should check if it's sensitive enough for your application, e.g. regarding noise level.

Is it OK that this product seems to have two long and separate leads? I'm used to trying to minimise the area of the loop between ground and tip at the end of a conventional passive probe.

 

[FvM]

Good point, if the measurement is taken in the near the NFC coupler coil, this active probe must be expected to pick up considerable signal by inductive coupling. I thought, you are looking for a differential probe. There should be better options for a small > 25 Mhz single ended active probe.

 

[maker8122]

Good point, if the measurement is taken in the near the NFC coupler coil, this active probe must be expected to pick up considerable signal by inductive coupling. I thought, you are looking for a differential probe. There should be better options for a small > 25 Mhz single ended active probe.

I looked on a few sites and had the impression that there are two kinds of active probes:

1) those that are designed for lower voltages (say up to 20v or 50v) and cost around 1000USD upwards;

2) those - a bit like this one - that seemed to be designed with measuring higher voltages in mind - and whose pricing starts lower down;

Since this one seems to offer the required capacitance am wondering if it could do the job. (Which amounts to checking peak voltage levels at Rx inputs to the controller chip and making adjustments so they're somewhere around 1-1.5v.)

Probably the best would be one of the "low voltage" probes but so far they all look a bit expensive (given this is all I really think I need it for)?