User Guide

RM-11

System Module CC Technical Documentation

System Connector

The immunity strategy concerning the bottom connector lines is to shield all lines to this

part in order to prevent radiation in the phone itself when an external accessory is

connected, and to prevent radiated fields from disturbing the lines as well. Appropriate

discrete filters close to the bottom connector are implemented for EMC and ESD

protection.

Mechanical Shielding

The RM-11 has a metal shield over the RF and BB parts to provide immunity for internal

radiation and immunity for external fields.

EMC Strategy

The phone must comply with the given CE requirements concerning EMC and ESD. The

goal is to pass internal SPR requirements. Therefore attention has been paid to obtaining

immunity in the PWB layout itself, and the implementation of filters in the circuit

design.

The baseband EMC strategy is divided into electrical and mechanical items. All electrical

guidelines, clocks, and high-speed signals should be routed in inner layers and away from

the PWB edges. Clock signals distributed to other circuits should have series resistors

incorporated to reduce rise times and reflections. Slew rate-controlled buffers should be

used on custom components wherever possible to reduce the EMC produced by the

circuit. Separate power supplies for digital, analog, and RF-blocks should be used as

much as possible. Baseband and RF supply power rails should be isolated from each other

by means of inductors in the power supply rail to prevent high-frequency components

produced on the baseband power supply rail to spread out over the RF power supply

plane. This might be required to avoid interference from digital circuits to affect the

performance of the RF section.

All external connectors and connections must be filtered using RC or LC networks to

prevent the high-frequency components from entering connection cables that then will

act as antennas. The amount of this type of EMC component is in straight relation to the

amount of external connections. The type of network and amount of components to be

used is determined by the AC and DC impedance characteristic of that particular signal.

Low-impedance signals require LC networks while medium-impedance level signals

(input signals at moderate bandwidth) can use RC networks.

The EMC protection should also prevent external or internal signals to cause interference

to the baseband and, in particular, to audio signals. Internal interference is generated by

the transmitter burst frequency and the switchmode charging. The transmitter burst

frequency interference is likely to cause noise to both microphone and earphone signals.

The transmitter RF interference is likely to cause more problems in the microphone

circuitry than in the earphone circuitry because the earpiece is a low-impedance

dynamic type.

As mechanical guidelines, the baseband and RF sections should be isolated from each

other using EMC shielding, which suppresses radiated interference. The transmitter burst

frequency can also generate mechanical vibrations that can be picked up by the