Telit Wireless Solutions GE863-QUAD - Manual (Page 38)

GE863-QUAD
GE863-PY
1vv0300715 Rev. 1 - 19/09/06
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Right reserved page 38 of 79
NOTE: In the unbalanced application the capacitor C3 shall be > 200nF otherwise the frequency
response will be cut at low band frequencies (down to 300Hz). This capacitor can be placed
close to the MIC- pad (MIC_HF- or MIC_MT- depending on the audio path chosen) or if
possible it should be placed close to the shielded cable connector. If the ground return path is
well designed, then it is possible to eliminate the C3 capacitor, provided the buffer is close to
the mic. input.
NOTE: The cable to the microphone should be shielded.
NOTE: The microphone changes with the value of R2. Usually the microphone sensitivity is
characterized with 2kΩ biasing resistance, so try to keep the value of R2 around 2kΩ. For mic.
characteristics refer to the manufacturer.