u-blox NINA-B112 System Integration Manual

Also see for NINA-B111: Manual Getting started

u-blox NINA-B112 System Integration Manual Manual pdf 29 page image

NINA-B1 series - System Integration ManualUBX-15026175 - R09 Design-inPage 29 of 49Figure 10: Transmission line trace designTo properly design a 50 Ω transmission line, the following remarks should be taken into account:• The designer should provide enough clearance from surrounding traces and ground in the same layer; ingeneral, a trace to ground clearance of at least two times the trace width should be considered and thetransmission line should be ‘guarded’ by ground plane area on each side.• The characteristic impedance can be calculated as first iteration using tools provided by the layoutsoftware. It is advisable to ask the PCB manufacturer to provide the final values that are usuallycalculated using dedicated software and available stack-ups from production. It could also be possible torequest an impedance coupon on panel’s side to measure the real impedance of the traces.• FR-4 dielectric material, although its high losses at high frequencies can be considered in RF designsproviding that :o RF trace length must be minimized to reduce dielectric losses.o If traces longer than few centimeters are needed, it is recommended to use a coaxial connectorand cable to reduce losseso Stack-up should allow for thick 50 Ω traces and at least 200 μm trace width is recommended toassure good impedance control over the PCB manufacturing process.o FR-4 material exhibits poor thickness stability and thus less control of impedance over the tracelength. Contact the PCB manufacturer for specific tolerance of controlled impedance traces.• The transmission lines width and spacing to GND must be uniform and routed as smoothly as possible:route RF lines in 45 ° angle or in arcs.• Add GND stitching vias around transmission lines.• Ensure solid metal connection of the adjacent metal layer on the PCB stack-up to main ground layer,providing enough vias on the adjacent metal layer.• Route RF transmission lines far from any noise source (as switching supplies and digital lines) and fromany sensitive circuit to avoid crosstalk between RF traces and Hi-impedance or analog signals.• Avoid stubs on the transmission lines, any component on the transmission line should be placed withthe connected pad over the trace. Also avoid any unnecessary component on RF traces.