SensorsのトピックRe: NFC EMI Issue

NFC EMI Issue

sjvg — Wed, 11 Aug 2021 17:16:14 GMT

1. Do we need a Shielded twisted pair for NFC antenna connection?Can we use an Unshielded twisted pair for a length of 150mm?

2. Is there any EMI/EMC issue experienced so far with NFC readers ?

Regards

Re: NFC EMI Issue

Fabian_R — Fri, 13 Aug 2021 21:38:57 GMT

Thank you for your interest in our products, we really appreciate it.

For cable antennas, we recommend using a 50 ohm shielded coaxial cable.

Just be sure to follow our matching circuit tutorial. Keeping in mind that one matching circuit should be right after the EMC filter and another Matching circuit should be at the other end of the coax cable.

Also bear in mind the Current Limitation of your Reader Board in your calculation.

I hope this information has been useful, thank you for using our community!

Re: NFC EMI Issue

sjvg — Mon, 16 Aug 2021 08:57:14 GMT

Hi Fabian

Thank you for the response.

The operation of NFC is near noise sources like Power supply, LCD etc. Tx/Rx output is differential. In ths scenario, can you explain how coax will help to mitigate EMI/EMC?

Regards

sjvg

Re: NFC EMI Issue

Fabian_R — Mon, 16 Aug 2021 17:25:31 GMT

Hello sjvg,

In order to create an EMC filter, it is required to follow the next recommendations, bear in mind that if the TX settings aren't properly done, your board could be damaged.

First of all, the TX settings must be adjusted, this can be done using NFC Cockpit. It is required to change the operating phase of each: TX1_INV_RM and TX2_INV_RM to ensure both are operating in 0. Make sure all EEPROM settings are adapted.

Also, instead of driving the 2 TX in serial, drive them in parallel. Instead of Z - 2 x 10 ≈ 20Ω. Use an unbalanced impedance Z = 10/2 ≈ 5Ω(unbalanced).

L0 and C0 with an EMC filter with fcutoff ≈ 14.5 … 15 MHz

- L0 ≥ Lant / 2 (to ensure the correlation)

• C1=> increase or decrease the impedance & adjust cable length

• C2=> adjust the cable length

Re: NFC EMI Issue

sjvg — Mon, 16 Aug 2021 17:36:13 GMT

Hi Fabian

Sorry, I think there is a confusion here. Here I am not mentioning on onboard EMI filter of NFC. I understand the usage from application note.

Is there an EMC issue in using a 150mm Twisted cable? Do we need to use a Shielded twisted pair while operating near noisy sources?

Will the performance or detection range will be reduced in the vicinity of power supply noise, LCD etc.?

Regards

sjvg

Re: NFC EMI Issue

Fabian_R — Mon, 16 Aug 2021 18:38:59 GMT

Hello sjvg,

I'm sorry but we cannot recommend you to use a twisted pair cable, this might cause noise in the NFC IC.

Please, use a shielded coaxial cable for connecting the antenna.

Re: NFC EMI Issue

sjvg — Tue, 17 Aug 2021 05:31:15 GMT

Hi Fabian

Thank you. When we use a coax, shield will be connected to one of the Tx lines and center conductor will be connected to second line in a differential line operation. Differential is balanced line operation and coax we are typically using in an unbalanced line. Also, twisted pair will cancel the noise as per my understanding. So my doubt is:

1. Will it really help us in this case?

2. Will it have any significant advantage than a twisted pair cable?

Request you to reply inline for each queries for a better understanding.

Regards

sjvg

Re: NFC EMI Issue

Fabian_R — Tue, 17 Aug 2021 16:41:44 GMT

We haven't tested a twisted pair solution, I'm sorry that this matter cannot be addressed the way you would like. The intention to use a different solution to what we recommend gets out of our support scope.