User Manual

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USERS MANUAL
22(42)
Document number Revision
4/198 17-LXE 108 566 Uen PA7
Application Implementation:
BIAS: An analog ground plane should be generated, which connects to GND in one
point so that high frequency digital current is not floating through the analog ground.
Connecting the analog ground in only one point also avoids ground currents from power
supplies and other high current circuitry from creating noise in the analog circuitry. The
voltage supply for the analog circuitry should connect its ground pin as close as
possible to the point where the analog ground connects to GND. The BIAS reference is
generated from this supply voltage and analog ground, and shall be used as a
reference for all analog circuitry in the application. Note that Analog Ground and AGND
are two different signals. Analog Ground is the ground plane used by the application. It
should be connected to the application’s GND in one point preferably at the regulator
that generates the analog supply voltage. AGND is the analog audio reference
received from the phone. This is a signal with the intent to be used together with ATMS
and AFMS as a semi differential interface between the module and the application.
Regulator
VIN
GND
R
R
VCC
BIAS
Analog Ground
ATMS: An application using the analog audio interface must re-reference the signal
from its own internal BIAS to AGND. The figure below shows an example of a
microphone implementation.
0
-
+
0
VCC
0
-
+
0
<=1k
BIAS
>=2.2uF
ATMS
AGND
>=2.2uF
+
+
The microphone should preferably be connected to its pre-amplifier differentially, which
will minimize noise pickup from possible ground current.