high noise when using DCDC in TX mode

[victor passe]

Hi, This is what constant carrier looks like at 2450MHz on my custom board using DCDC disabled

This is with DCDC enabled:

It can also look much worse with no real peak and just a wide band of energy,

I have followed the reference schematic in the product spedification. What could be the problem?

[AmbystomaLabs]

It's broadband noise because it is PWM and the duty cycle isn't constant since the load isn't constant.

The noise is largely a function of your layout but also component parasitics play a role. Not all passives are created equal even though vendors like to tell you otherwise.

Soldering can be an issue too. Wetting on a QFN can be problematic sometimes and the poorly wetted connection has its own parasitics that add to the mess. You should do a visual inspection under a microscope just to confirm well wetted connections. You might want to pull a few just to make sure your vendor properly pasted the epad.

[Hung Bui]

Dear customer, 

Due to limited staff during the holiday period, we unfortunately can't handle your case before we get back to the normal staff by the first week of January 2019. We are sorry indeed for the delay. We wish you a great holiday and a Happy New Year 2019. 

Best Regards, 

Nordic Tech Support Team  

[Andreas]

Hi,

 

Your span is a little narrow, what's inside will drown in the carrier. How does what's outside compare, and how does the spectrum look when the carrier is modulated?

Your C6 is larger than we recomend (1nF), though I do not expect any large effects from changing this you might want to try it.

 

Best regards,

Andreas