User Guide

RH-21 Company Confidential
System Module Nokia Customer Care
Page 18  2004 Nokia Corporation. Issue 2 07/2004
tracks have been drawn with respect to shielding by having ground plane over tracks,
and ground close to the tracks at the same layer.
All edges are grounded from both sides of PWB and solder mask is opened from these
areas. Target is that any ESD pulse faces ground area when entering the phone; for
example, between mechanics covers. All holes in PWB are grounded and plated through
holes.
LCD
ESD protection for LCD is implemented by connecting metal frame of LCD in to gnd. Con-
nection is only on one side, at the top of the LCD.
Microphone
Microphone signals are input lines and therefore very sensitive to radiated fields. Immu-
nity 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 is applied for both internal and
external microphone lines. Microphone is an unsymmetrical circuit, which makes it well
protected against EMC.
EAR Lines/MIDI
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 coils are
used in series with the speaker for immunity against incoming fields from the speaker.