5.9.2 Auxiliary Audio from Mobile Station (AUXO)

AUXO is a single-ended auxiliary analogue audio output from the wireless modem and may be used to drive a speaker or an earpiece. The interface has an internal 100nF coupling capacitor; a load of 10kohm will provide a near full-scale output capability between 300 to 4300 Hz.

The table below shows the audio signal levels for AUXO.

Parameter

 

Conditions

 

Min

 

Typ

 

Max

 

Unit

 

 

 

 

 

 

 

 

 

 

 

Output voltage full scale

 

RL =10kΩ

 

670

 

750

 

840

 

mVrms

Frequency response

 

-3dB cut-off (RL =10kΩ)

225

 

 

 

 

 

Hz

5.9.3 Microphone Signals (MICIP, MICIN)

MICP and MICN are balanced differential microphone input pins. These inputs are compatible with an electret microphone. The microphone contains a FET buffer with an open drain output, which is supplied with at 2.4V ±10% relative to ground by the wireless modem as shown below.

Figure 5.9-1 Microphone connections to the wireless modem

The input low-noise amplifier stage is constructed out of standard low-noise op amps. External resistors set the gain of this stage.

The input gain is scaled by the input resistors to be around 18, which provides optimal performance for many standard types of electret microphones. The module provides a microphone bias at 2.4V, and can supply at least 1mA of current.

LZT 123 1834

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