Reference Design
2.
L2
This is the ground layer for returned signals. In the reference design, an opening is provided on L2 underneath
the 50 Ω RF transmission line, and another two openings are provided underneath the signal output pads of the
32 MHz crystal to reduce parasitic capacitance. L3 acts as the reference ground where openings are provided on
L2.
Figure 4-8 L2 design for 4-layer PCB (QFN56)
3.
L3
This layer is used for the power and a small number of routes. In the reference design, L3 is used as the reference
ground layer for the RF transmission line, and therefore the part underneath the RF transmission line shall be
complete.
Figure 4-9 L3 design for 4-layer PCB (QFN56)
4.
Bottom layer
This layer is used for filter components layout and signal routing. Filter components should be as close to the
corresponding IC pins as possible.
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