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PN7150 AGC question in understanding system

Question asked by Daniel Tomicek on Jul 11, 2018
Latest reply on Jul 18, 2018 by Estephania Martinez

Hi, we are currently bringing up a PN7150 chip on a custom NFC coil and are following the AN11755, Antenna Design and Matching Guide

 

I have a question on the Rx tuning path in understanding the AGC in tuning in reader mode page 3.6.3
Rx resistance selection process.

 


I understand that the higher the AGC, the more attenuation is done on the Rx signal.

 

What don't understand is why does the AGC need to be between 500 and 800 with no tag on top for tuning. Perhaps we don't fully understand the role of the AGC, but it seems as if we would want a lower AGC value with no Tag on top so then there is more headroom for attenuation when a card comes in.

 

Can someone help explain why the AGC needs to be between these two values, or else point to some documentation we can look at aside from the AN11755?

 

In addition, what are the effects of having a lower AGC with no Tag?

 

Thanks! 

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