Nokia RH-9 Series Ccs Technical Documentation page 64

RH-9
System Module & UI
implementing a low impedance path for ESD. This is done by an open gold layer of
0,7mm at both sides of the pwb.
Keyboard
The keyboard PWB layout consists of a grounded outer ring and either a "trefoil pattern"
grid (matrix) or an inner pad. This construction makes the keys immune for ESD, as the
keydome will have a low ohmic contact with the PWB ground.
Power ON Key
The power ON key interface on UEM (PWRONX) is protected via RC filtering and con-
trolled PWB layout.
PWB lines and filters concerning immunity
Audio lines
In order to obtain good signal to noise ratio and good EMC/ESD immunity the audio lines
has been carefully routed with respect to obtaining low impedance in the signal path
and obtain a proper shielding.
Microphone lines
Microphone signals are input lines and therefore very sensitive to radiated fields.
Immunity for radiated fields is done by routing the microphone lines in shielded layer 5
and in parallel for obtaining a low impedance path and with respect to a common noise
point of view in the signal path. This is applied for both internal and external microphone
lines. Microphone lines from the bottom connector are routed on layer 2 to the filters
and at layer 5 from filters to the UEM IC.
The ESD/EMC protection circuits are C101, C102, C103 and Z100 for Internal micro-
phone and Z101 for external microphone.
EAR lines
EAR lines are output signals, also routed on shielded layer 5, to obtain immunity for
conducted emission towards UEM. Internal EAR lines are EMC/ESD protected by radiated
fields from the earpiece by Z150 and further suppressed by the low impedance signal
path in the pwb.
Page 64 ãNokia Corporation
CCS Technical Documentation
Issue 1 11/02