Analog Ground Vs. Agnd; Microphone Path; Figure 27: Microphonei - Wavecom CM52 Integrator's Manual

Analog ground vs. AGND

3.4.2
The AGND signal output from the Wireless CPU
connected to the main ground and used by the Wireless CPU
Under any circumstances it should not be used as a ground or connected to application's ground.
AGND must be treated as a signal. Together with ATMS and AFMS it creates a semi differential
interface. The analog ground shall be used as ground plane for the analog circuitry of the
application. It should not be connected to the AGND signal output from the phone module.

Microphone path

3.4.3
An application using the analog audio interface must re-reference the signal from its own internal
BIAS to AGND received from the Wireless CPU
The figure below shows an example of a microphone implementation.
The microphone should preferably be connected to its pre-amplifier differentially which will
minimize noise picked up along the way from the microphone to its amplifier. If the impedance is
the same on both microphone lines, and the lines are run in parallel, the same amount of noise is
picked up on both lines. This noise is then removed in the differential amplifier stage.
CM52 Integrators' Manual
WI_DEV_CM52_UGD_001-001
Page 45 of 53
C3
VCC
R1
R3
C2
R2
-
C2
R2
+
R3
R1
C3
Figure 27: Microphone Implementation Example
This document is the sole and exclusive property of WAVECOM. Not to be distributed or divulged without prior written agreement.
Ce document est la propriété exclusive de WAVECOM. Il ne peut être communiqué ou divulgué à des tiers sans son autorisation préalable
is not a ground. It is an analog reference,
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in one place inside the Wireless CPU
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.
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0
R4
-
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R4
+
BIAS
CM52 Integrators' Manual
C5
R5
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<=1k >=2.2uF
0
+
R5 >=2.2uF
+
C5
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ATMS
AGND