Sierra Wireless AIRPRIME WISMO218 - Manual (Page 97)

WA_DEV_W218_PTS_002 Rev 006 April 29, 2010 97
7. Noises and Design
7.1. EMC Recommendations
The EMC tests have to be performed as soon as possible on the application to detect any possible
problems.
When designing a GSM terminal, make sure to take note of the following items:
 Possible spurious emissions radiated by the application to the RF receiver in the receiver
band.
 ESD protection is mandatory for all peripherals accessible from outside (SIM, serial link,
audio, AUX_ADC0, etc.).
 EMC protection on audio input/output (filters against 900MHz emissions).
 Biasing of the microphone inputs.
 Length of the SIM interface lines (preferably <10cm).
 Ground plane: It is recommended to have a common ground plane for analog/digital/RF
grounds.
 It is recommended to use a metallic case or plastic casing with conductive paint.
Note: The AirPrime WISMO218 does not include any protection against overvoltage.
7.2. Power Supply
The power supply is one of the key issues in the design of a GSM terminal.
A weak power supply design could affect the following items in particular:
 EMC performances
 The emissions spectrum
 Phase error and frequency error
Note: Careful attention should be paid to the following:
Quality of the power supply: low ripple, PFM or PSM systems should be avoided (a PWM converter is
preferred).
Capacity to deliver high current peaks in a short time (pulsed radio emission).