noise on Vdd ST25R3911B

[loich]

Hi,

I have some noise on the Vdd pin of the ST25R3911B.

I send the fieldon() command and there is a huge noise at 27MHz frequency on the Vdd (8) pin.

Below is a screenshot of the refdesign disco Vdd pin with the fieldon and the noise observed on my board (same base time). There is a huge difference between them. It is a problem for me because when the tag is at field limit, I have rfal error (err 9) and this error is not present on the demokit. I think it comes from this noise.

There are 100nF and 10uF decoupling caps on the Vdd. Here is the routing of the reader

It seems that the reader generates noise at the crystal oscillator frequency. What can I do to reduce this noise? Any idea?

Best Regards

[Ulysses HERNIOSUS]

Hi,

have you looked through AN5043 (Layout recommendations for the design of boards
with ST25R3911B/ST25R391x devices) already?

BR, Ulysses

[loich]

Hi Ulysses,

Thank for your reply.
Yes I read this document. Normally, I have respected these recommendations. For information, I did not have this noise on my previous design. There is a difference, but I cannot find it.
Do you know why a 27MHz glitch is on Vdd line and how to filter it?

Best Regards,

Loïc

[Travis Palmer · Accepted solution]

Hello Loic,

the most critical blocks are the RFO driver and its supply VSP_RF and VSN_RF as well as VDD supply and the crystal oscillator connection. 

You can try to improve the filtering of the VSP_RF/VSN_RF caps. (and VDD decoupling)

As an example, below the VSP_RF/VSN_RF decoupling of the ST25R3911B-DISCO.

You can try to solder the capacitors (0402 preferable) directly across the pins on your current design, to see if it does a difference. 

Additional (new) tips can also be found in the AN6279  of the ST25R300. You have to filter the content, which do not apply for the ST25R3911B. ( e.g. Crystal placement and routing is fine for all ST25R products).

BR Travis