I'm thinking of using a digital MEMS microphone in a project - looks like it would save on some parts: no need for an amplifier and ADC. The output from the microphone is PDM and I'd need to convert it PCM for any useful processing.
Say I'd like to work with 16-bit, 48 kHz audio. Seems like the answer is to oversample 64x by clocking the microphone at 3.072 MHz, then low-pass filter and decimate the output. What's the effective number of bits (ENOB) I get out of this?
If the microphone datasheet claims 60 dB SNR (just less than 10 bits), and 64x oversampling gives me 2.5 bits (1 bit for every 4x oversampling), then I'm only getting in the neighborhood of 12-13 bits. Is this calculation right?
FWIW, the parts I was considering are http://www.mouser.com/ds/2/720/DS45-1.01%20AKU240%20Family%20Datasheet-552987.pdf or http://www.mouser.com/ds/2/389/DM00121815-524679.pdf. They seem fairly close in specs.