User's Manual

HiLo3G-850 User Manual
04 March 2011 - Page 32 / 36
Audio tracks must be larger than 0.5 mm.
8. Recommendations on layout of customers board
8.1 General recommendations on layout
There are many different types of signals in the module which are disturbing each other. Particularly, Audio signals are
very sensitive to external signals as VBAT... Therefore it is very important to respect some rules to avoid disruptions or
abnormal behavior.
Magnetic field generated by VBAT tracks may disturb the speaker, causing audio burst noise. In this case, modify
layout of the VBAT tracks to reduce the phenomena.
8.1.1. Ground
A ground plane as complete as possible
Ground of components has to be connected to the ground layer through many vias not regularly distributed.
Top and bottom layer shall have as much as possible of ground planes. Flood the empty remain surface of the layout of
those two layers with a ground plane connected to main ground with as much vias as possible.
8.1.1.1 Ground layout guidelines
Proper grounding is crucial to end-product performance. At least one layer must be a dedicated ground plane. This
ground plane is the common point referenced by all end-product circuits.
In addition to the dedicated ground plane layer, any unused space on all PCB layers should be filled with ground to
provide the most robust grounding from layer to layer.
Bypass capacitors should be connected directly to their surface layer ground fill. Multiple vias should connect each
capacitor directly to the main ground plane, with one via in the capacitor‘s pad plus several vias within the surface layer
ground fill area.
8.1.1.2 Digital ground
Digital ground should via directly to the main ground plane. In addition, each layer between layers 1 and main ground
should include ground fills directly below the center grid area‘s digital pins, with each stack of vias connecting to each
ground fill area. The large mass of copper tied together using this technique provides the best possible electrical ground and
thermal conductivity.
8.1.1.3 Analog/RF ground
The analog/RF ground pins are connected together with one another, but isolated from the digital ground (until main
ground). Like the digital pins, the analog/RF pins should via directly to the main ground plane. In addition, each layer
between layers 1 and main ground should include ground fills directly below the outer layer‘s analog/RF pins, with each
stack of vias connecting to each ground fill area. The large mass of copper tied together using this technique provides the
best possible electrical ground and thermal conductivity.
8.1.2 Power supplies
Layer for power supply signals (VBAT, VGPIO) is recommended.
Any loop of power signals layout must be avoided on the design.
Suitable power supply (VBAT, VGPIO) track width and thickness.
8.1.3 Clocks
Clock signals must be shielded between two grounds layer and bordered with ground vias.
8.1.4 Data bus and other signals