Installation Instructions

LISA-U2 series - System Integration Manual

UBX-13001118 - R19 Early Production Information Design-In

Page 118 of 175

35 µm

270 µm

760 µm

L1 Copper

L3 Copper

L2 Copper

L4 Copper

FR-4 dielectric

380 µm 500 µm500 µm

Figure 57: Example of 50  coplanar waveguide transmission line design for the described 4-layer board layup

35 µm

1510 µm

L2 Copper

L1 Copper

FR-4 dielectric

1200 µm 400 µm400 µm

Figure 58: 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 or TXLine from Applied Wave Research, 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 example of Figure 57 and Figure 58)

 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 57, 1510 µm in Figure 58)

 the dielectric constant of the dielectric material (e.g. dielectric constant of the FR-4 dielectric material in

Figure 57 and Figure 58)

 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 57, 400 µm in Figure 58)

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 microstrip, use the “Coplanar Waveguide” model for the 50  calculation.

Additionally to the 50  impedance, the following guidelines are recommended for the RF line design:

 Minimize the transmission line length; the insertion loss should be minimized as much as possible, in the

order of a few tenths of a dB