Honored Contributor
Honored ContributorHi,
A starting point would be to directly decimate the input signal to 100Msps without overheads i.e. by just discarding every other sample. Since your analogue signal is filtered down to 40MHz then 100Msps is enough without any sampling rule violation. This should not affect the information content. Thus you can do all filtering at 100Msps. Any further decimation has to take into account the aliasing that may result. So you can't just go down without prior filter. You may also consider using one set of coefficients(maximum) then decimate the set to get your corner frequency
