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8.
Noises and Design
EMC Recommendations
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.
Power Supply
The power supply is one of the key issues in the design of a GSM terminal and careful attention
should be paid to the following:
•
Quality of the power supply: low ripple, PFM or PSM systems should be avoided (using a
PWM converter is preferred).
•
The capacity to deliver high current peaks in a short time (pulsed radio emission).
A weak power supply design could affect the following items specifically:
•
EMC performances
•
The emissions spectrum
•
Phase error and frequency error
Overvoltage
The WISMO228 does not include any protection against overvoltage.
WA_DEV_W228_PTS_002
Rev 001
Product Technical Specification &
Customer Design Guidelines
Page 109 of 109
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