Patent ID: 7130434

Claim:
An electret microphone assembly comprising: a multilayer printed circuit board; an electret microphone comprising an electret diaphragm and backplate coupled to the printed circuit board; a field effect transistor with a gate coupled to the electret backplate, a drain coupled to provide audio frequency output to an audio output node, and a source terminal coupled to a ground; and a resistor with a first end coupled to the drain of the field effect transistor and a second end coupled to a filter, wherein the filter attenuates unwanted electromagnetic interference associated with a radio frequency transmitter, wherein the filter comprises: a capacitor comprising: 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; a first inductor comprising a via coupled to the active layer within the multilayer printed circuit board; and a second inductor comprising a via coupled to the active layer within the multilayer printed circuit board.