User Guide

PAMS Technical Documentation System Module
NSB-5
Issue 1 03/01 Nokia Mobile Phones Ltd. Page 31
Figure 12: Audio Control
The baseband supports three microphone inputs and two earphone outputs. The inputs
can be taken from an internal microphone, a headset microphone or from an external
microphone signal source. The microphone signals from different sources are connected
to separate inputs at the COBBA–GJP asic. Inputs for the microphone signals are differ-
ential type.
The MIC1 inputs are used for a headset microphone that can be connected directly to the
system connector. The internal microphone is connected to MIC2 inputs and an external
pre–amplified microphone (handset/handfree) signal is connected to the MIC3 inputs. In
COBBA there are also three audio signal outputs of which dual ended EAR lines are used
for internal earpiece and HF line for accessory audio output. The third audio output AUX-
OUT is used only for bias supply to the headset microphone. As a difference to DCT2 gen-
eration the SGND does not supply audio signal (only common mode). Therefore there are
no electrical loopback echo from downlink to uplink.
The output for the internal earphone is a dual ended type output capable of driving a
dynamic type speaker. The output for the external accessory and the headset is single
ended with a dedicated signal ground SGND. Input and output signal source selection
and gain control is performed inside the COBBA–GJP asic according to control messages
from the MAD2. Keypad tones, DTMF, and other audio tones are generated and encoded
by the MAD2 and transmitted to the COBBA–GJP for decoding.
Internal Microphone and Earpiece
The baseband supports three microphone inputs and two earphone outputs. The inputs
can be taken from an internal microphone, a headset microphone, or from an external
microphone signal source. The microphone signals from different sources are connected
to separate inputs to the COBBA_GJP asic. Inputs for the microphone signals are of a dif-
ferential type.
System
Connector
Pre
& LP
D
MIC1
LP
A
D
MIC3
MIC2
EAR
HF
AuxOut
MCU
Buzzer
DSP
Buzzer
Driver
Circuit
MAD
Bias +
EMI
XMIC
XEAR
SGND
EMI+ACC
Interf.
EMI
Preamp
Multipl.Premult.
Amp
Multipl.
COBBA
A
EMI
Slide
Display