On a reader embedding MFRC630+, after matching the antenna, we saw that the measured pulse shape according to ISO14443A is not conform.
**** Without any tag near the reader
t1=3us, t2=0us, t3=2.4 us and t4=0.4us
**** With a tag near the reader
t1=3us, t2=1.34us, t3=1.8us and t4=0.6us
1. When should be measured the pulse shape? with or without tag?
2. What could be the impacts when the pulse shape is not good?
3. How to improve this pulse shape?
To be honest, I do not know the specification at that specific level. Nevertheless, as long as the application note for antenna design is followed, it shall work fine: https://www.nxp.com/docs/en/application-note/AN11019.pdf
As mentioned in the same App note, the Tx envelope shape can be changed if necessary. For more specific information about pulse width, please refer to chapter 4.3.1 for Type A. As you can see in the chapter, no optimization is needed, but it can be adjusted in the TXDataModWidth register if necessary.
Hope it helps.
thank you for your reply.
We tried to modified the registers by using the same values as defined in figure Fig 38. Example of Tx overshoot protection (100% ASK envelope) of AN11019. We do not get the same results. We don't see the impact of setting OvershootT1 = 4h.
What could be the problem in our board?
I cannot say for sure because of the different hardware, but basically there are two overshoots (T1 and T2). The amplitude in overshoot timer T1 is related to the main amplitude (set_cw_amplitude), whilst the amplitude in overshoot T2 is denoted by set_residual_carrier.
Knowing the previous relation between timers overshoots and amplitudes, please make the corresponding adjustments that best suit your target hardware. You might be interested to refer to an example for optimizing the rising edge for type A @ 106 kBit/s in case of overshoots after fig 37 in AN11019, thank you for your comprehension.