Figure 2 shows a block diagram of a PDM-output MEMS microphone and Figure 3 shows a typical I2S-output digital microphone. The I2S microphone contains all of the digital circuitry that a PDM microphone has, as well as a decimation filter and serial port.
A MEMS microphone package is unique among semiconductor devices, in that there is a hole in the package for the acoustic energy to reach the transducer element. Inside this package, the MEMS microphone transducer and the analog or digital ASIC are bonded together and mounted on a common laminate. A lid is then bonded over the laminate to enclose the transducer and ASIC. This laminate is basically a small PCB that's used to route the signals from the ICs to the pins on the outside of the microphone package.