The present invention provides a solution to the needs described above
through a microphone PCB with an integrated filter. The invention
provides for an electret microphone assembly. The microphone assembly
includes a multilayer printed circuit board. A field effect transistor
with a gate is coupled to the electret microphone. The field effect
transistor drain is coupled to provide audio frequency output to an audio
output node, and the field effect transistor source is coupled to a
ground. A first end of a resistor is coupled to the drain of the field
effect transistor and the second end is coupled to a filter. The filter
attenuates unwanted electromagnetic interference associated with a radio
frequency transmitter. The filter includes a filter capacitor made of a
ground layer coupled to ground within the multilayer printed circuit
board, an active layer within the multilayer printed circuit board
coupled to the second end of the resistor, and a dielectric layer
disposed between the ground layer and the active layer. The filter
further includes a first and second inductor comprising vias coupled to
the active layer within the printed circuit board.