STM32F103RB ADC Noise

jamie · ‎2014-05-27

Posted on May 27, 2014 at 17:06

Hi

I'm having problems with noise on the STM32F103RB ADC.

At the VDDA pin there is 20mV pk-pk noise from a

300KHz

switch regulator.

I am using the recommended 1uF || 10nF caps on the pin.

I was going to add a series ferrite to block the switching noise but when I came to look for the design steps it looks like ferrites are for noise in the MHz range.

Can anyone advise on options for putting a simple filter stage between my 3V3 rail and VDDA pin to attenuate the 300KHz switching noise.

I would like to attenuate by an order of magnitude, it is currently 20mV pk-pk

Any help would be highly appreciated

Thanks

raptorhal2 · ‎2014-05-27

Posted on May 27, 2014 at 20:28

Fix the source of the problem. TO-220 or D-Pak voltage regulators have less than a millivolt noise.

The ferrites will attenuate processor MHz switching noise ringing back up the VDD pins.

Cheers, Hal

jpeacock2399 · ‎2014-05-27

Posted on May 27, 2014 at 21:24

Many buck regulators put a LOT of capacitance on the output side, on the order of 50-100uF. Try the brute force method, put a big cap on the output side of the regulator (and watch the ESR, use a low ESR like an aluminum cap). Doesn't hurt to have some larger caps on the input side too, depending on what kind of source for your power.

Jack Peacock

jamie · ‎2014-05-28

Posted on May 28, 2014 at 09:12

Thanks to both of you for the info.

chen · ‎2014-05-28

Posted on May 28, 2014 at 10:15

Hi

''Fix the source of the problem.''

Definitely!

A further note:

'' TO-220 or D-Pak voltage regulators have less than a millivolt noise.''

Note sure if he meant - replace your ''

300KHz

switch regulator'' with a Voltage regualtor.

If he mean put one in series with your switching regulator - be aware Voltage regulators can still pass high frequencey noise, I have been investigating building hybrid PSUs (Switching back end and Voltage Regulator front end - to reduce the power dissipation in the voltage regulators but have found that VRs do pass high freq noise).

Also, check if the ADC has a separate supply/reference input. If so, you can use a separate supply/reference to the ADC from the rest of the processor. This is a common trick to reduce noise to ADC/DACs and keep PSU efficiency.