SL871 Family Product User Guide
1VV0301170 Rev. 9
Page 58 of 89
2021-07-15
Not Subject to NDA
However, if a good quality external LNA is used, the noise figure of that LNA (typically
better than 1dB) could reduce the overall system noise figure from 4 dB to approximately
2 dB.
RF Trace Losses
RF Trace losses on a PCB are difficult to estimate without having appropriate tables or
RF simulation software. A good rule of thumb would be to keep the RF traces as short as
possible, make sure they are 50
Ω
impedance and don’t contain any sharp bends
.
Figure 17: RF Trace Examples
PCB Stack and Trace Impedance
It is important to maintain a 50
Ω
impedance on the RF path trace. Design software for
calculating trace impedance can be found from multiple sources on the internet. The best
method is to contact your PCB supplier and request a stackup for a 50
Ω
controlled
impedance board. They will give you a suggested trace width along with PCB stackup
needed to create the specified impedance.
It is also important to consider the effects of component pads that are in the path of the
50
Ω
trace. If the traces are shorter than a 1/16th wavelength, transmission line effects
will be minimal, but stray capacitance from large component pads can induce additional
RF losses. It may be necessary to ask the PCB vendor to generate a new PCB stackup
and suggested trace width that is closer to the component pads, or modify the component
pads themselves.
Содержание SL871
Страница 1: ...SL871 Family Product User Guide 1VV0301170 Rev 9 2021 07 15 Telit Technical Documentation...
Страница 89: ......