My customer is using the ADMP421 digital microphone and are working to improve the way we monitor the output of the microphone. They cannot find a document that describes the format of the PDM output from the ADMP421 anywhere on the ADI web site. The data sheet shows when the data is output relative to the clock input, but it does not describe the format of the data itself. They know it’s pulse density modulation, but that could mean a lot of things. What does the data do when there is no sound, positive sound pressure on the microphone, and negative sound pressure on the microphone? Does the data change at a sub-multiple of the clock frequency, such as clock/64?
Anything you can provide on this is greatly appreciated. The microphone is working on their boards but they think they are only measuring either positive sound pressure or negative sound pressure, but not both.