Nokia NSE-3 SERIES, Service Manual

Page: 17 / 217

PAMS
Technical Documentation
NSE–3
System Module
Page 3 – 11
Original 11/97
The interface between the baseband and the RF section is handled by a
specific asic. The COBBA asic provides A/D and D/A conversion of the
in–phase and quadrature receive and transmit signal paths and also A/D
and D/A conversions of received and transmitted audio signals to and
from the UI section. The COBBA supplies the analog TXC and AFC sig-
nals to rf section according to the MAD DSP digital control and converts
analog AGC into digital signal for the DSP. Data transmission between the
COBBA and the MAD is implemented using a parallel connection for high
speed signalling and a serial connection for PCM coded audio signals.
Digital speech processing is handled by the MAD asic. The COBBA asic
is a dual voltage circuit, the digital parts are running from the baseband
supply VBB and the analog parts are running from the analog supply
VCOBBA.
The baseband supports three external microphone inputs and two exter-
nal earphone outputs. The inputs can be taken from an internal micro-
phone, a headset microphone or from an external microphone signal
source. The microphone signals from different sources are connected to
separate inputs at the COBBA asic.
The output for the internal earphone is a dual ended type output capable
of driving a dynamic type speaker. Input and output signal source selec-
tion and gain control is performed inside the COBBA asic according to
control messages from the MAD. Keypad tones, DTMF, and other audio
tones are generated and encoded by the MAD and transmitted to the
COBBA for decoding. A buzzer and an external vibra alert control signals
are generated by the MAD with separate PWM outputs.
EMC shieding is implemented using a metallized plastic B–cover with a
conductive rubber seal on the ribs. On the other side the engine is
shielded with a frame having a conductive rubber on the inner walls,
which makes a contact to a ground ring of the engine board and a
ground plane of the UI–board. Heat generated by the circuitry will be con-
ducted out via the PCB ground planes.