Audio Interface
30 Module Hardware Description January 1, 2006
Figure 2-18 shows the microphone circuit and Table 2-7 gives the microphone specifications.
Figure 2-18: Headset Microphone Circuit
Important: The headset microphone circuit design depends on the type of microphone device.
A series capacitor is required in case a passive microphone is used, or the
application provides a separate bias voltage to an active microphone circuit.
The internal G24 biasing circuit may also be used with an active microphone, which
corresponds to the headset microphone port specifications.
Speaker Port
The analog speaker port is the G24 power-up default active output for voice calls and DTMF
tones. It is located at pins 67 and 69 on the G24 interface connector, named SPKR_N and
SPKR_P respectively.
It is designed as a differential output with 32Ω impedance, but may also be used as a single-ended
output referenced to the G24 analog ground.
The speaker output is used for both the handset and the headset audio paths.
Table 2-7:
Headset Microphone Port Specifications
Parameter Conditions Min Typ Max Unit
Input Voltage No load
AT+MMI CG= 0
2.0 V
PP
Gain Programmable in
1 dB steps
031dB
AC Input
Impedance
1kΩ
Bias voltage R
BIAS
= 2.2 kΩ
I
BIAS
= 1 mA
22.12.2V
Bias Current 1 mA
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