Electronic – Boost converter noise

adcboostmicrophonepower supply

I'm trying to prototype a hobby project on a breadbaord.
I'm using an electret microphone + opamp to feed MCU ADC with audio signal.
When I'm using a regulated power supply I get good signal with relatively low noise.

Now I wanted to power it with battery using a step up boost converter – but got a serious noise problem on the amplified signal.
Since it's a hobby project I don't have the equipment (scope) to find the exact characteristis of this noise, I only know it's bad enough to completely ruin my audio input, and that it comes from the boost converter since I don't get it when I use regulated power supply or when connecting the circuit directly to batteries.
Tried to add decoupling caps, but it didn't help much. I even tried adding another low dropout regulator (s81230ag) before the opamp and adc analog power but the noise is still there.

How would you recommend to proceed?

  • Is there a simple way (small number of components, on a breadboard) to filter this noise with the existing components this and this?
  • Should I try a differnt boost converter, perhaps with switching frequence high enough so it could be filtered by the mic amplified circuit?
  • Pehaps I should use a differnt amplifying circuit for the mic which is less susceptible to power supply noise?

Best Answer

There are two potential problems with the booster you've chosen. Firstly, it's specified as having 30 mV ripple and if your Mic circuit is producing output signals close to the supply rails then you'll get this ripple superimposed. Secondly your amp has a power supply rejection spec that may be poor and this will produce noise on the feed to your ADC. Thirdly, the switcher is a type that works best under medium load conditions and if your amp is only taking 10mA or less the switching frequency will be quite low and possibly ripple will be higher. Try loading the 3v3 with 100 ohms and see if this improves things.

Fourthly, your electret Mic power feed should have two resistors from the power rail and a 10uF cap down to ground to further reduce supply ripple superimposed on the Mic signal.