Ublox MAX-7C-0 Manual

Contents

Ublox MAX-7C-0 Manual Manual pdf 22 page image

MAX-7 / NEO-7 - Hardware Integration ManualUBX-13003704 - R09 Production Information DesignPage 22 of 52 For multi layer boards the distance between micro strip line and ground area on the top layer should at leastbe as large as the dielectric thickness. Routing the RF connection close to digital sections of the design should be avoided. To reduce signal reflections, sharp angles in the routing of the micro strip line should be avoided. Chamfersor fillets are preferred for rectangular routing; 45-degree routing is preferred over Manhattan style90-degree routing.AntennaAntennaAntennaPCBPCB PCB123456789101112131428272625242322212019181716151234567891011121314282726252423222120191817161512345678910111213142827262524232221201918171615wrong better bestFigure 14: Recommended micro strip routing to RF pin Do not route the RF-connection underneath the receiver. The distance of the micro strip line to the groundplane on the bottom side of the receiver is very small (some 100 μm) and has huge tolerances (up to 100%).Therefore, the impedance of this part of the trace cannot be controlled. Use as many vias as possible to connect the ground planes. In order to avoid reliability hazards, the area on the PCB under the receiver should be entirely covered withsolder mask. Vias should not be open. Do not route under the receiver.3.3.5 Antenna micro stripThere are many ways to design wave-guides on printed circuit boards. A common factor to all is that calculationof the electrical parameters is not straightforward. Freeware tools like AppCAD from Agilent or TXLine fromApplied Wave Research, Inc. are of great help in this regard. They can be downloaded from www.agilent.com orwww.hp.woodshot.com and www.mwoffice.com.Micro strip is the most commonly used configuration on printed circuit boards and shown below in Figure 15and Figure 16. As a rule of thumb, to achieve a 50  line impedance with FR-4 material, the width of theconductor is roughly double the thickness of the dielectric.Note: For the correct calculation of the micro strip impedance, one does not only need to consider the distancebetween the top and the first inner layer, but also the distance between the micro strip and the adjacent GNDplane on the same layerUse the Grounded Coplanar Waveguide model for the calculation of the line dimensions.