Damien Cahill <damiencahill@AUSTARNET.COM.AU> wrote

>I have a reasonably simple question. I am currently routing an RF PCB which
>uses a 1GHz DDS synthesiser. The RF signals on the board are up to 400MHz
>in frequency and obviously I must consider the impedance of any copper
>tracks I lay. What I am unsure of though is what impedance should I be
>aiming for with these tracks. Should it match the DDS outputs which are all
>50ohm or should it be as low impedance as possible to reduce resistive
>losses.

You should always match the traces impedance to the output ot the
devices driving them. For FR-4 substrate material 1.6mm thick and
0.035mm cooper layer on it you can make microstrips with 2.91 mm
wide traces over a ground plane. That will give you 50Ohms impedance
over a wide range of frequencies. I'd be more concern with reflections of
the signal than with any other issues. There are simulators available to
check signal integrity on the PCB. If your product is going to pass some
regulatory agencies tests, then try to minimize emissions as well.
VV
P.S. This is a botton posting so I don't get responses to my own answer
and so unnecessary traffic on the list.



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