PN7160 disturbance

[ethan_dang1]

During a test, it was found there had disturbance with the GND of the mainboard During NFC TX process. 

The VBAT and VDD(up) all connected to the battery.

Is there any way to improve it? 

Is it useful to reduce the transmit power?

How to reduce the TX power through software or hardware?

[KellyLi]

Hello @ethan_dang1 

Thanks for contacting us and choosing the NXP products.

Based on your description, I would like to know if all of your boards have this phenomenon?

Reducing the power might have some effect. But only by modifying the hardware. method is to lower the VDD(tx) voltage.

Best Regards,

kelly

[ethan_dang1]

I see the following description from Datasheet, does it mean that I can modify VDD(tx) by software

 Battery voltage is 4V ，modify core configuration parameters PMU_CFG Byte7&Byte9 like this

[KellyLi]

Hello @ethan_dang1 

Yes, you’re absolutely correct, the output of the TXLDO can be configured via NCI commands. It was my negligence and say sorry to you. But the RF signal is coupled to GND, which should be closely related to PCB LAYOUT, or can you share your GND waveform diagram?

Best Regards,

Kelly

[ethan_dang1]

FYI,Thanks!

[Tomas_Parizek · Accepted solution]

Hello ethan_dang1, 

Let me try to help you with your issue. 

• What scope probe are you using for measurement? Is it a passive or active one? 
• How do you measure the noise on GND ?

As my colleague said, this noise could be related to the PCB layout. Generally, you should follow the recommendations described in the PN7160 HW design guide + follow the GND rules. 

About the power settings, you can do it via HW as well as SW. 

HW: 

• Matching impedance directly defines the output power of the PN7160 
  • See https://www.nxp.com/docs/en/application-note/AN13892.pdf -> 6 How to adjust the output power

SW: 

• As you wrote, the output power can be adjusted via LDO register settings -> So you can reduce the VDD(Tx) voltage to 3V 
• You can also reduce the output power via "CLIF_ANA_TX_AMPLITUDE_REG" 
  • GSN value and TX Amplitude 
  • 

Anyway since you radiate quite high RF power by your antenna which is typically close to the PCB with electronic. So I expect that some RF noise can be always measured on the device due to the magnetic coupling (signal or GND loops). 

BR

Tomas 

[ethan_dang1]

Thank you very much！ I see