I've built a circuit which detects ambient audio through an electret microphone, amplifies the audio signal using a LM386 op amp (gain = 200), and then processes that audio information. The board is powered through a LM2623 boost converter, which ramps up a 3.7V LiPo battery to 5V for the power rails on the board.
The op amp circuit is set up like the gain=200 diagram in its datasheet. The converter is set up according to the typical application schematic in its datasheet .
The LM2623 (and, from what I understand, many boost converters) produces small oscillations on the 5V-GND rails - typically no more than 1% peak-peak. This wouldn't pose an issue at all, except that the audio signal my op amp is supposed to amplify is also very small.
I have 100 uF and 1 uF capacitors between 5V-GND before and after the converter, as well as near the op amp.
It seems that my op amp is amplifying the oscillations on the 5V-GND rails, thereby ruining my audio data. I've confirmed that it is indeed the oscillations because the oscillations and op amp output are in sync and have the same frequency. I am wondering how I can avoid this problem. Since the boost converter cannot get away from rippling the output, I would like to know how to prevent the op amp from picking up this noise, or if there is something more crucial I may be missing.
