Q-factor CLRC663 antenna

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Q-factor CLRC663 antenna

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Contributor I

Hi,

For a project I'm using the CLCR663 plus IC to read out Desfire EV2 cards.

As it's a battery powered application we are using the low power card detection feature of the CLRC663.

Because of this LPCD we want our antenna design to have the highest possible Q-factor to have the best detection range in LPCD mode.

We tested various design options with Q-factor up to 100 and still have good readout results and detection range. In this application note (AN11019) however it is suggested that for a bit-rate of 106 kbit/s the Q-factor should be 25.

As this is an application note and not a specification I'm curious to find out if you have suggestions/spec for the maximum Q-factor in this application. I could not find a spec for this in the datasheet.

Best regards,

Marijn

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IvanRuiz
NXP TechSupport
NXP TechSupport

Hello,

Please allow us some comments on your statements:

  1. First of all, according to internal team, they have never seen a proximity system with such high Q… 
    1. A single component of the overall system might have a Q = 100 (e.g. then antenna coil itself), but that does not mean an overall Q = 100.
    2. How measured (see below)?
  2. Secondly, the Q has nothing to do with the power as such: we have to distinguish between impedance and Q (-> losses).
    1. The impedance defines the power consumption, therefore typically for battery-powered devices we see a higher impedance (like 30 Ohm or even higher). It must be clear that a higher impedance results in lower current consumption, but also in a lower operating distance.
    2. The Q is defined by many parameters in the system. The interesting definition is related to the data transfer, which is made to be able to get enough bandwidth to transfer the data properly. Higher data rates require a higher bandwidth (= lower Q). The “symmetrical” tuning (like with PN5180 and PN7462) typically can use a higher Q than the “asymmetrical” tuning (as required with RC663).
  3. How to measure the Q? It is really difficult to measure it in NFC, because it depends on:
    1. With or without active TX? If active, with which power level?
    2. With or without tag? If with tag, in which distance?
  4. The Q factor is indirectly defined via the data transfer measurements with ReferencePICCs (ISO or NFC or EMVCo). That includes all relevant parameters (power level and tag, all components).

Hope this information helps you to have a better performance of your system.

BR,

Ivan.

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