CM52 Integrators’ Manual
WI_DEV_CM52_UGD_001-001
Page 31 of 53
CM52 Integrators’ Manual
Analog Reference (AGND)
The AGND lead is the analog audio reference ground. It is the return signal for Audio To Mobile
Station (ATMS), Audio From Mobile Station (AFMS).
Electrical characteristics: Imax < 40 mA (peak)
The AGND is connected to the chassis Ground (GND) in the CM52 Wireless CPU
®
, and only
there. The application should be connected to GND and only use AGND as reference for the
audio lines ATMS and AFMS.
AGND and GND are not to be connected together in the application.
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 Wireless CPU
®
and the application.
Figure 14: BIAS Diagram Example
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.
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