User Guide

PAMS
Technical Documentation
NSE–8/9
System Module
Page 2– 65
Issue 1 07/99
Table 33. Internal uplink audio Baseband specifications
Parameter min typ max Unit Comment
Mic Bias current 100 500 uA Max supply by the cobba
Microphone sensitivity –2 42 +2 dB 0dB = 1V/Pa @ 1kHz
Internal cobba gain 18 dB set by MCU SW in cobba regis-
ter
total internal cobba gain –0.5 38 +0.5 dB 300 < f <3400 Hz
Signal level at cobba
MiC2P/N input
25 mV 300 < f <3400 Hz, to not satu-
rate the Cobba input stage with
Cobba gain (MCU value) 18 dB
below 200mV
BB HP filter f
–6dB
135 Hz
Internal Cobba HP filter En-
abled
Earphone, down link audio:
The internal down link audio circuitry consists of basically 3 blocks:
1. The cobba ASIC:
Which converts the PCM bitstream from the speech processor in
the DSP to analog signals which are feed to the earpiece.
2. The earpiece unit:
Which converts the voltage variations to air pressure variations
(sound). The low impedance (32 ohm), dynamic type internal ear-
phone is connected to the PCB by means of mounting springs for
automatic assembly.
3. EMC suppression:
L202 and L203 prevents the RF radiated by the antenna from get-
ting demodulated in by the earpiece in the low impedance output of
the Cobba. Additionally are added 27pF capacitors to remove GSM
signals coupled to the earpiece wires in the PCB from the cobba
output to the earpiece unit.
Table 34. Internal downlink audio Baseband specifications
Parameter min typ max Unit Comment
Earphone sensitivity –3 103 +3 dB @1mW at 1KHz
Internal cobba gain –10 dB set by MCU SW in cobba regis-
ter
total internal cobba gain –0.5 –10 +0.5 dB 300 < f <3000 Hz
Key press and user function response beeps are generated with the
earpiece.