Ublox SARA-N210, Руководство по системной интеграции

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SARA-N2 series - System Integration Manual
UBX-17005143 - R06 Design-in Page 35 of 82
Figure 16 and Figure 17 provide two examples of proper 50  coplanar waveguide designs. The first
transmission line can be implemented in case of 4-layer PCB stack-up herein described, the second
transmission line can be implemented in case of 2-layer PCB stack-up herein described.
35
µ
m
35
µ
m
35
µ
m
35
µ
m
270
µ
m
270
µ
m
760
µ
m
L1 Copper
L3 Copper
L2 Copper
L4 Copper
FR-4 dielectric
FR-4 dielectric
FR-4 dielectric
380
µ
m 500
µ
m 500
µ
m
Figure 16: Example of 50

coplanar waveguide transmission line design for the described 4-layer board layup
35
µ
m
35
µ
m
1510
µ
m
L2 Copper
L1 Copper
FR-4 dielectric
1200
µ
m 400
µ
m 400
µ
m
Figure 17: Example of 50  coplanar waveguide transmission line design for the described 2-layer board layup
If the two examples do not match the application PCB layup, the 50

characteristic impedance
calculation can be made using the HFSS commercial finite element method solver for
electromagnetic structures from Ansys Corporation, or using freeware tools like AppCAD from
Agilent (
www.agilent.com ) or TXLine from Applied Wave Research ( www.mwoffice.com ), taking care
of the approximation formulas used by the tools for the impedance computation.
To achieve a 50  characteristic impedance, the width of the transmission line must be chosen
depending on:
 the thickness of the transmission line itself (e.g. 35
µ
m in the example of Figure 16 and Figure 17 )
 the thickness of the dielectric material between the top layer (where the transmission line is
routed) and the inner closer layer implementing the ground plane (e.g. 270
µ
m in Figure 16 , 1510
µ
m
in Figure 17 )
 the dielectric constant of the dielectric material (e.g. dielectric constant of the FR-4 dielectric
material in
Figure 16 and Figure 17 )

the gap from the transmission line to the adjacent ground plane on the same layer of the
transmission line (e.g. 500
µ
m in Figure 16 , 400
µ
m in Figure 17 )
If the distance between the transmission line and the adjacent GND area (on the same layer) does not
exceed 5 times the track width of the micro strip, use the “Coplanar Waveguide” model for the 50

calculation.