User Guide

PAMS
Technical Documentation
NSE–8/9
System Module
Page 2– 66
Issue 1 07/99
External Audio
The external audio of NSE–8/9 is designed only for support of the Janette
Accessory program units:
– PPH–1 Carkit with and without external microphone HFM–8
– HDC–5 button headset
The PPH–1 uses Cobba input MIC1 since to output from PPH–1 is higher
there is less gain in the NSE–8/9 Baseband. HDC–5 uses MIC3, since
the headset microphone generates a weaker signal there is need for
higher amplification in the NSE–8/9 Baseband.
Uplink signal path
The uplink audio circuitry consists of basically 7 blocks:
1. Input from the external device
1..a The HDC–5 microphone device:
Which is connected by cable directly to the bottom connector
X503. It converts air pressure variations to current variations.
1..b The PPH–1 output is a well conditioned analog voltage con-
nected by cable directly to the bottom connector X503, if
HFM–8 is used. If HFM–8 is not used the uplink audio is han-
dled by internal microphone of NSE–8/9
2. DC circuitry:
2..a The HDC–5 microphone bias circuitry:
AUXOUT from Cobba generates a 2.1V dc suppply, which is
filtered by R205 and C206 for better TDMA suppression.
R206, R231 and R232 converts the current variations created
by the microphone to a voltage variation.
2..b In PPH–1 conversation the DC circuitry plays no important
role. AUXOUT from Cobba generates 0V. The DC levels are
determined by the PPH–1 unit.
3. Filtering:
3..a With PPH–1 with HFM–8 the uplink signal is filtered by the first
order high pass filter (made by R217, R218, C207,C210, the
input impedance of the Cobba MIC1 port) to suppress low fre-
quency noise, especially from car environment.
3..b With HDC–5 the uplink signal is filtered through the same
stages as 3..a with an additional HP filter (made by C208,
C213 and the input impedance of the Cobba MIC3 port) to
suppress low frequency noise, especially from car environ-
ment even further. The usage of the input impedances from
the not used Cobba stages is possible since they are biased
no matter which input is used.