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GM47/GM48 INTEGRATOR’S MANUAL
48
LZT 123 7263 R1C
2.6 Analogue Audio
ATMS is the audio input, and AFMS is the audio output, of the module.
These signals can be used in Hands-free or Portable Hands-free mode.
Hands-free Mode
This mode is used for audio accessories, such as car kits and hands-free
equipment.
Portable Hands-free Mode
This is the default mode. It activates a different amplification factor in
the ME, and activates a 2V microphone bias level for ATMS. The bias
level is adjustable using AT*E2EAMS.
2.6.1 Audio To Mobile Station - ATMS
ATMS is the analogue audio input to the module. Internally, the signal
is sent to the CODEC (COder/DECoder), where it is converted to digital
audio in PCM (Pulse Code Modulation) format. The encoded audio is
sent to PCMOUT via the internal PCM bus.
ATMS provides a DC bias when it is used as the microphone input in
Portable Hands-free applications. All other sources must be
a.c.-coupled to avoid attenuation of low frequencies, and to prevent
incorrect biasing or damage to the ATMS input. Use a capacitor greater
than the value shown in the table below.
The ATMS input is a passive network followed by the transmit part of
the CODEC.
Pin Signal Dir Description
57 AFMS O Audio from mobile station
59 ATMS I Audio to mobile station
60 AGND - Ground (return) for analogue audio
Parameter Limit
Application driving impedance (0.3 - 3.5kHz) ≤300Ω
AC coupling capacitance
a
≥1µF
Module input impedance (0.3 - 3.5kHz) >50kΩ
Low frequency cut-off (-3dB) 300Hz ± 50Hz