Specifications

Rev 1 Dec.10 Proprietary and Confidential - Specifications subject to change 95
8
8: Design Guidelines
This chapter provides general design guidelines for the AirPrime
SL808X Embedded Module.
Caution: This chapter is under development—all recommendations must be
considered as ‘TBD’.
For industrial assembly guidelines, refer to [7] Customer Process
Guidelines—AirPrime SL Series, available from your Sierra Wireless
account representative.
8.1 General rules and constraints
Clock and other high frequency digital signals (e.g. serial buses)
should be routed as far as possible from the AirPrime SL808X
Embedded Module analog signals.
If the application design makes it possible, all analog signals should
be separated from digital signals by a ground line on the PCB.
Tip: It is recommended to avoid routing any signals under the AirPrime
SL808X Embedded Module on the application board.
8.2 PCB layout recommendations
Ground slugs should be reflowed on to the host PCB with <25%
voiding to allow effective heat dissipation.
8.3 Power supply
The power supply is one of the key issues in the design of a GSM
terminal.
A weak power supply design could, in particular, affect:
• EMC performance
• The emission spectrum
• The phase error and frequency error
When designing the power supply, careful attention should be paid to
the following:
• The quality of the power supply—low ripple, PFM or PSM
systems should be avoided; linear regulation or PWM converters
are preferred for low noise.