Motorola 8900 - Blackberry Curve Cell Phone OEM Car Charger, Developer'S Manual

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Chapter 2: Hardware Interface Description
December 15, 2008 C24 Module Hardware Description 27
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 1.8V through a 2.2k
Ω
resistor, and has an impedance of 1k Ω .
Figure 2-16 shows the microphone circuit and Table 2-7 gives the microphone specifications.
Figure 2-16: 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 C24 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 C24 power-up default active output for voice calls and DTMF
tones. It is located at pins 67 and 69 on the C24 interface connector, named SPKR_N and
SPKR_P respectively.
Table 2-7: Headset Microphone Port Specifications
Parameter Conditions Min Typ Max Unit
Input Voltage No load 1.6 V
pp
Gain Programmable by
AT Command 9 36 dB
AC Input
Impedance Freq=1Khz 1 k Ω
Bias voltage R
BIAS
= 2.2 k Ω
I
BIAS
< 1 mA
1.8 V
Bias Current 1 mA