Headset Microphone Port - Motorola G24 Developer's Manual

Figure 2-17
Figure 2-17: Handset Microphone Circuit
Important:

Headset Microphone Port

The headset microphone port is designed for use with, but not limited to, a headset audio device.
It is located at pin 57 on the G24 interface connector, named HDST_MIC.
It is designed as a single-ended input and should be referenced to the G24 analog ground.
The microphone input includes all the necessary circuitry to support a direct connection to a
headset microphone device. It incorporates an internal bias voltage of 2.1V through a 2.2kÙ
resistor, and has an impedance of 1kΩ.
January 1, 2006
shows the microphone circuit and
The 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 microphone port specifications.
Table 2-6: Handset Microphone Port Specifications
Parameter Conditions
Input Voltage No load
AT+MMICG=0
Gain Programmable in
1 dB steps
AC Input
Impedance
Bias voltage R
BIAS
I = 1 mA
BIAS
Bias Current
Module Hardware Description
Chapter 2: Hardware Interface Description
Table 2-6 gives the microphone specifications.
Min Typ
0
1
= 2.2 kΩ 2 2.1
Max Unit
2.0 V
PP
31 dB
kΩ
2.2 V
1 mA
29