I'm trying to connect the ADA8691 amplifier with ADMP411 microphone, but I can't find the input resistance of the amplifier. Thanks,
Just to follow up with this.. I heard back from the engineer of this part. The AD8691 is one of the older parts so unfortunately, it does not have Rin specs. However, its Ibias spec of 1pA should clue you in that it has very high input impedance. It is safe to assume a value in the high Mohms or Gohms range.
I hope this helps!