PCB considerations for filter

[brmadhukar]

Hi,
At what frequencies (for 2,4,6,8 layer boards) can I start considering the layout or placement for passive band pass filters, or do component values dictate the placement.

 

[brmadhukar]

Hi,
I also need to switch the bandwiths of the filters. What is the best way to do this. Is it mechanical (provide jumpers) or can I use analog switches. If I use analog switches should I consider any specific for say 15MHz filter.
TIA

 

[flatulent]

line lengths

The trace lengths compared to a wave length is the criteria. This ratio should be very small. Also the inductive coupling between inductors should be minimized. This is done by laying out so they are not near each other and have their axis at right angles to the nearest one.

As far as switching values, it depends upon the paasitic on resistance and off capacitance of the switches. Are you going to set the filter once for the life of the circuit or several times? If once, just load the prpoer part values. If several times, use solder jumpers.