Rainbow Electronics GM862-QUAD-PY - Manual (Page 43)

GM862-QUAD / PY Hardware User Guide
1vv0300748 Rev. 5 - 20/09/07
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 43 of 68
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.
8.4.2 Unbalanced Microphone Biasing
The unbalanced microphone biasing 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 unbalanced microphone biasing can be: