Sierra Wireless WISMO218 - Manual (Page 103)

WA_DEV_W218_PTS_002 Rev 005 Page 103 of 109
Product Technical Specification &
Customer Design Guidelines
7. Noises and Design
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 WISMO218 does not include any protection against overvoltage.
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
Caution: 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).