Integration Manual

Table Of Contents
TOBY-L3 series - System Integration Manual
TSD-19090601 - R13 System Integration Manual Page 83 of 143
35 um
35 um
35 um
35 um
270 um
270 um
760 um
L1 Copper
L3 Copper
L2 Copper
L4 Copper
FR-4 dielectric
FR-4 dielectric
FR-4 dielectric
380 um 500 um500 um
Figure 32: Example of a 50 coplanar waveguide transmission line design for the described 4-layer board layup
35 um
35 um
1510 um
L2 Copper
L1 Copper
FR-4 dielectric
1200 um 400 um400 um
Figure 33: Example of a 50 coplanar waveguide transmission line design for the described 2-layer board layup
If the two examples do not match the application PCB stack-up, 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 Avago / Broadcom AppCAD
(https://www.broadcom.com/appcad), 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 µm in the examples of Figure 32 / Figure 33)
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 µm in Figure 32, 1510 µm in Figure 33)
the dielectric constant of the dielectric material (e.g. dielectric constant of the FR-4 dielectric material in
Figure 32 and Figure 33)
the gap from the transmission line to the adjacent ground plane on the same layer of the transmission
line (e.g. 500 µm in Figure 32, 400 µm in Figure 33)
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.