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Telit GE863-QUAD / GE863-PY
Hardware User guide
1vv0300697, Rev. ISSUE#0, - 21/11/05
Reproduction forbidden without Telit Communication written authorization – All Right reserved – Right of modification reserved
page 30 of 69
6.3.1
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.
NOTE: The cable to the microphone should not be shielded, instead a twisted pair cable shall be
used.
NOTE: The microphone sensitivity changes with the value of R2 and R3. Usually the microphones
are characterized with 2kΩ biasing resistance, so try to keep the sum of R2 and R3 around 2kΩ.
Refer to your microphone manufacturer for the mic. characteristics.
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