Micrel, Inc.

MICRF620

December 2005

18

M9999-120205

Layout

Recommended Land Pattern

Figure 12 shows a recommended land pattern that

facilitates both automatic and hand assembling.

Figure 13. Recommended Land Pattern (TOP VIEW)

Layout Considerations

Except for the antenna input/output signal, only digital and

low frequency signals need to interface with the module.

There is therefore no need of years of RF expertise to do a

successful layout, as long as the following few points are

being followed:

•

Proper ground is needed. If the PCB is 2-layer, the

bottom layer should be kept only for ground. Avoid

signal traces that split the ground plane. For a 4-

layer PCB, it is recommended to keep the second

layer only for ground.

•

A ground via should be placed close to all the

ground pins. The bottom ground pad should be

penetrated with 4-16 ground vias.

•

The antenna has an impedance of ~50 ohm. The

antenna trace should be kept to 50 ohm to avoid

signal reflection and loss of performance. Any

transmission line calculator can be used to find the

needed trace width given a board build up. Ex: A

trace width of 44 mil (1.12 mm) gives 50

impedance on a FR4 board (dielectric cons=4.4)

with copper thickness of 35

µm and height (layer 1-

layer 2 spacing) of 0.61 mm.