NFC input resistance to fixed value

RE: NFC input resistance to fixed value

ketiljo — Tue, 19 May 2020 08:57:14 GMT

If you set the following registers:

0x40005604 = 0x00015014 (This disables the automatic input voltage adjustment)

0x40005634 = 2

0x40005638 = 2

You should get an Rin of around 1 kohm. If you want to measure this exactly, you can set NFC2 to ground and NFC1 to 2.8 V and measure the DC current. Increase the resistance by writing 1 to the two last registers, and decrease by writing 3.

RE: NFC input resistance to fixed value

T IJ — Fri, 15 May 2020 13:45:33 GMT

The supply voltage is set to 2.8V I believe.

RE: NFC input resistance to fixed value

ketiljo — Fri, 15 May 2020 13:42:53 GMT

It's possible to set a fixed resistance value. This depends on the supply voltage. If you can tell me the supply voltage you're using I'll see if I can get the number to write to the register.

The reason you don't the the NFC to work is probably because the resistance value it too low.

RE: NFC input resistance to fixed value

T IJ — Fri, 15 May 2020 06:27:03 GMT

As we are still testing and developing our system I want to know if it is possible to select a certain resistance value on the input. This could also be a set of fixed resistances.

We have most of the times a fixed distance between the antenna's and we want to know how our circuit behaves on different input resistances without it automatically changing its resistance.

RE: NFC input resistance to fixed value

ketiljo — Thu, 14 May 2020 11:48:27 GMT

The input resistance is variable as this is part of the automatic gain control. With a fixed resistance value, you will have problems reading the tag as the amplitude will be dependent on the distance between the tag and the reader.

It's also correct that the NFC is not operational unless the test registers are set to 0. These registers are only for testing and antenna measurements.