Specifications

Product Technical Specification & Customer Design Guidelines

Interfaces

3.11.5 Design Recommendation

3.11.5.1

General

When speakers and microphones are used outside, it is recommended to add ESD

protection as close as possible to the speaker or microphone, connected between the

audio lines and a good ground.

The microphone connections may be either differential or single-ended in MIC1, but

using a differential connection is strongly recommended to reject common mode

noise and TDMA noise.

While using a single-ended connection in MIC1 or AUXI, ensure to have a good

ground plane, a good filtering as well as shielding, in order to avoid any disturbance

on the audio path. It is recommended to use the Q64 Wireless CPU

AREF pin for the

good plane connection.

It is important to select the appropriate microphone, speaker and filtering components

to avoid TDMA noise

3.11.5.2 Recommended Microphone Characteristics

The microphone impedance must be around 2 KΩ.

Sensitivity from -40dB to –50 dB.

SNR > 50 dB.

Frequency response compatible with the GSM specifications.

To reduce TDMA noise, it is highly recommended to use microphones with two

internal decoupling capacitors:

• CM1=56pF (0402 package) for the TDMA noise generated by the

demodulation of the GSM 850 and GSM900 frequency signal.

• CM2=15pF (0402 package) for the TDMA noise generated by the

demodulation of the DCS/PCS frequency signal.

The capacitors must be soldered in parallel to the microphone.

Page: 63 / 116

This document is the sole and exclusive property of WAVECOM. Not to be distributed or divulged without

prior written agreement.

WA_DEV_Q64_PTS_001-003 January 9, 2009

Figure 22: Microphone