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.

 

Parameter

 

 

Conditions

 

Min

 

 

Typ

 

 

Max

 

 

 

Unit

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Input voltage full scale

 

 

max input gain

 

14

 

 

16

 

 

18

 

 

 

mVrms

 

 

 

min input gain

 

45

 

 

50

 

 

56

 

 

 

mVrms

 

 

 

 

 

 

 

 

 

 

Frequency response

 

 

-3dB cut-off

 

300

 

 

 

 

 

3400

 

 

 

Hz

 

Output dc bias level

 

 

 

2.16

 

2.4

 

2.64

 

 

 

V

LZT 123 1836

50