Hello,
I am trying to use ICS-40619 analog MEMS microphones in a demo rig. We have soldered the microphone to a wire (see 1st attachment).
On the other side of this cable, we connected a 3V power supply and a BNC connector (see 2nd attachment). At the power supply, we connected a 0,1 muF capacotor. At the output side we connected 1 muF capacitors.
We tested the microphone using two different measurement systems, while having it receive a 1000 Hz, 94 dB sine wave. The microphone wirks, but the measured signal looks kind of strange. Unfortunately, I don't have a measured signal at hand, but I've drawn what is looks like (see 3rd attachment). The sine wave looks fine, apart from a weird bump at the negative peak.
The only things that we believe are different from the connection instruction are:
1. The capacitor at the power supply is located at the far end of the cable, rather than close to the connector on the microphone.
2. We did not use ceramic capacitors.
3. The capacitors on the signal side have a lower capacity (1 muF vs. 2.2 muF), because we are hooking it up to a port with high input impedance (117 kOmh).
We can't explain why the measured signal looks so strange. I hope someone here can help us understand what mistakes we may have made. Can our problem be explained by one of the points mentioned above, or did we make another mistake?
Thanks in advance.
regards,
Thijs Hekman