WM_PRJ_Q2400_PTS_005 -00718th January 2006Confidential©All rights reservedPage: 27 / 51This document is the sole and exclusive property of WAVECOM. Not to bedistributed or divulged without prior written agreement.A/ Differential connectionImpedance of the microphone input in differential mode:• Module ON: R in = 10 kΩ +/-10 %• Module OFF: R in >1 MΩ +/-10 %Typical implementation:L1L2C1 C2C4C3MIC1PMIC1NVCCC5R1R2R3R4Figure 14: MIC1 inputs (differential connection)R1 = R4 = from 100 to 330 Ω.R2 = R3 = usually between 1 kΩ and 3.3 kΩ as per the microphonecharacteristics.C1 = 33 pF to 47 pF.C2 = C3 = C4 = 47 F to 100 pF.C5 = 47 μF.L1 = L2 = 100 nH.R1 and R4 are used as a voltage supply filter with C5.C1 has to be the nearest possible to the microphone. Microphone manufacturersprovide this capacitor directly soldered on the microphone.C2 has to be very close to the WISMO module connector.L1, L2, C3 and C4 has to be put near the WISMO module connector and can beremoved according to their environment (ground plane, shielding ...etc). Thebest way is to plan all the components and to remove those which are notnecessary to filter out the TDMA noise on the audio path.
