This is a low-cost, small-size audio pre-amplifier for MEMS microphone, OPAMP-based circuit amplifies the low-level analog signal coming from MEMS microphone to the desired level required for the next stage which is an audio amplifier, basically microphone level to line level.
Resistor R4 and R7 are used to generate a voltage reference to bias the input common-mode voltage of the op-amp at VCC/2, C7, C8, and R7 help to reduce power supply noise. R5 and C5 allow AC coupling of the microphone signal. R2 and C2 create a low-pass gain so as not to amplify noise beyond the audio bandwidth. R3 and C6 create a high-pass gain so as not to amplify the DC biasing of the op-amp (including input offset voltage). The cut-off frequency is 59 Hz. D1 is a power LED, this board has a dual option for MEMS microphones. Users may solder onboard microphones or connect external microphones. This board is tested with external Analog MEMS microphone modules from PUI Audio which comes with 3 connections VCC, GND, and output.
Pre-Amplifier for MEMS Microphone – [Link]