User Manual

GM862-QUAD / PY Hardware User Guide

1vv0300748 Rev. 5 - 20/09/07

8.4 Microphone Biasing

The electret microphones usually need a biasing voltage to work properly. Refer to your microphone

provider for the characteristics required.

NOTE: The microphones have a hot wire were the positive biasing must be connected. Usually

it is indicated by a + symbol or a red point. If the polarity of the bias is reversed, then the

microphone will not work properly. For this reason be sure to respect the mic. biasing polarity.

8.4.1 Balanced Microphone Biasing

The balanced microphone bias voltage should be obtained from a dedicated voltage regulator, in order

to eliminate the noise present on the power lines. This regulator can be the same for all the audio

paths. The microphone should be supplied from a capacitor multiply circuit.

For example a circuit for the balanced microphone biasing can be:

NOTE: In the balanced application the resistors R2 and R3 must have the same value to keep

the circuit balanced.