Telit Wireless Solutions GM862-GPS - Manual (Page 31)

GM862-GPS Hardware User Guide
1vv0300728 Rev. 0 - 27/04/06
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Right reserved page 31 of 55
5.4 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.
5.4.1 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.