instrumentation amplifier & anti-aliasing

The main point of using an instrumentation amplifier is that it has differential inputs with good common mode rejection. If you try to turn a differential input into part of a filter, you will almost certainly mess up the common mode rejection, not to mention needing extra parts for each input. Why not just use a separate op-amp filter stage?

Also, depending on exactly what you are using the ADC for, you may be better off not using any filter at all. You need a filter if you want to be able to handle any arbitrary input without aliasing, but I have found that there are huge numbers of applications where this isn't really needed. And if it *is* really needed, it usually needs something a whole lot beefier that the simple few poles you are likely to want to build yourself.

Tell us about your application and we may be able to give specific advice.

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis Shareware from Interstellar Research