User Guide

CC Technical Documentation System Module
RM-11
Issue 1 02/2004 ©2004 Nokia Corporation Confidential Page 23
All edges are grounded from both sides of the PWB and a solder mask is opened from
these areas. The purpose is for any ESD pulse to face a ground area when entering the
phone (i.e., between mechanics covers). All holes in the PWB are grounded and plated
through holes.
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 to ESD, as the
key dome has a low ohmic contact with the PWB ground.
Audio Lines
In order to obtain good signal-to-noise ratio and good EMC/ESD immunity, the audio
lines have been carefully routed with respect to obtaining low impedance in the signal
path and obtaining proper shielding.
Microphone Lines
Microphone signals are input lines and therefore very sensitive to radiated fields.
Immunity for radiated fields is done to obtain a low-impedance path and with respect to
a common noise point of view in the signal path. This applies for both internal and
external microphone lines.
EAR Lines
EAR lines are output signals, also routed on layer 2 and 7, to obtain immunity for
conducted emission from the UEM. Internal EAR lines are EMC/ESD protected by radiated
fields from the earpiece by the low-impedance signal path in the PWB.
The same PWB outline has been implemented for the SALT speaker. Low ohm coil
inductors are used in series with the speaker for immunity against incoming fields from
the speaker.
Charger Lines
The ground from the charger is connected directly to a common PWB ground for a low
impedance path to the battery. The positive charger line is ESD, EMC, and short-circuit
protected by appropriate circuits.
HEADINT
The HEADINT line is EMC/ESD protected by routing on shielded layer 2 and by placement
of resistor R154 close to the bottom connector.
Battery Supply Filtering
Battery supply lines to the UEM IC are filtered with LC filters. These filters provide
immunity against conducted RF noise.