I would like to sample the output of an analog MEMS microphone with an ADC embedded in a uC, sampling rate up to 1MHz.
I don't care too much about signal quality (as I'm more interested in ambient noise level than anything else). I want to absolutely minimize the footprint of the overall solution.
Application notes typically show a DC blocking capacitor at the output of the MEMS microphone, followed by a simple OpAmp stage that provides some gain and sets a suitable DC offset for subsequent ADC sampling.
I would like to do something even simpler and avoid the OpAmp. I would just pass the microphone output signal through a low-pass RC filter (so no DC blocking) and sample that. It seems to me that would exploit correctly the ADC dynamic range, given that:
- My ADC would be set to have a 0-3V conversion range.
- My MEMS microphone (Knowles SPW0430HR5HB - acceptable VDD range 1.5V-3.6V) is specified with a DC output = 0.72V when VDD=1.5V (so DC output=VDD/2); I would use it at VDD=3V so I assume the DC output would then be 1.5V. In which case I can directly sample the microphone output (unchanged DC level) with my ADC without clipping.
Do you see any flaw in that reasoning? One concern I have is whether the DC level at the output of the MEMS is really proportional to VDD.