On Jul 16, 5:30*pm, "orien1202" <saharmonfa...@yahoo.ca> wrote:

and if it is what is the best anti-aliasing filter that
> would preserve phase?
> thanks

I am involved in many applications where preserving phase is
important. To preserve phase the type of anti-aliasing filter is not
that important, but how you implement it is. We use very stable
precision caps/resistors that have very low drift over time/
temperature, then model the inverse of the transfer function of the
anti-aliasing filter in software, then compensate for any phase errors
introduced by the filter. We also generally use a delta-sigma A/D for
phase important applications, as it simplifies the anti-aliasing
filter, and therefore the cost (since the precise resistors/caps are
not cheap or physically small)