User Guide

PAMS
Technical Documentation
NSE–8/9
System Module
Page 2– 64
Issue 1 07/99
Internal Audio
Microphone, uplink audio:
The internal uplink audio circuitry consists of basically 5 blocks:
1. The microphone device:
Which converts air pressure variations to current variations. The in-
ternal microphone is placed in a well in the bottom connector part,
it’s connected to the bottom connector by means of mounting
springs for automatic assembly.
2. The microphone bias circuitry:
MBIAS from Cobba generates a 2.1V dc suppply, which is filtered by
R214 and C220 for better TDMA suppression. R215 and R216 con-
verts the current variations created by the microphone to a voltage
variation.
3. Filtering:
The microphone signal are filtered by the second order high pass
filter (made by R219, R220, C226,C229,R230,C258,C259 and the
input impedance of the Cobba MIC2 port) to suppress low frequency
noise, especially from car environment (since the internal mic is
used for Handsfree unit PPH–1)
4. Conversion:
The Cobba GJP ASIC converts the analog audio signal to a PCM
bitstream which is supplied to the DSP for further speech processing
5. EMC protection:
The microphone unit are equipped with two internal capacitors for
removal of RF noise generated by the phones own PA via the an-
tenna and demodulated by the FET inside the mic device. Additional
27pF capacitors are inserted to remove GSM signals coupled to the
mic wires in the PCB from the bottom connector to the Cobba input.
EDS protection are made up by V200.