I am developing PDM MEMS mic with ADAU1451. We are using 48k UltraSound Mems. What is decimation ratio on ADAU1451 PDM Mic interface? Is it adjustable?
No, it is always 64x fs.
So you will need to send it 3.072MHz clock to obtain 48kHz sample rate.
However, if this helps, you can send the PDM input signal to an ASRC where you can sample rate adjust it to match the core's sample rate. So you could run the microphone's sample rate much slower and convert it up to the core fs rate. This will allow you to run the core much faster. Just keep in mind the ASRC ratio is 1:8 so if the core is running at 192kHz fs you could only run the PDM mic down to 24kHz fs and still be able to convert it to 192kHz.
As I mentioned, we are using 48k Bandwith therefore we need at least 96k sample rate.
Is there any way to get higher Sampleing Rate of Digital MEMS mic interface?
Otherwise, is it needed PDM to I2S solution?
Our PDM to I2S converter, the ADAU7002, is also fixed at 64x but it is able to run at 96kHz. So that is probably an option.
I am wondering if you have found a mic that can actually produce an output with that bandwidth at a decent SNR? The mics I know about will not be able to do that so the PDM modulator does not matter if you will not have signal there.
So I suggest you obtain an evaluation board and try it out. It would be a while before I could setup a test here and try it out.
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