designing with AD8421 is really a nice thing, because this device has superb performance characteristics making it a very good part. However looking at following questions related to it shows it has some hidden pit falls, too.
This is similar to its faster and more current hungry equivalent AD8429.
What to make sure, that such things won't happen?
How about you do you found any other point for these InAmps, or are some of my hints not hitting the right point?
If this is general design consideration to optimized the AD8421 or any inamp performance please add my inputs below:
What is your intended applications? Just let us know if you need any assistance.
thank you for the good advice and hints.
The application is just a analog signal conditioning front end for a measurement system. As there are several switchable gain setting stages, we tried to use the AD8421 as wide band programmable gain amplifier.
It works, but currently has some gain peaking issues in range around 2MHz to 8 MHz, due to a not as optimal layout as it could be. This increased system noise to a higher level then expected, because RF rectification and similar things have side effects into measured signal range. (Well it is not really noise but it looks quite similar.)
An improved pcb layout might solve these issues, however that's currently a pure trial and error approach, as there're few measures to track down the origin of noise and gain peaking. (hard to say if simulation models are accurate even down to such parasitic levels, and pcb modifications are time consuming and hard to do).
Anyway your hints give good points to look out for.
Note: AD8422 has even a much more flat frequency response then AD8421 -> If smaller bandwidth of AD8422 is OK -> it will be the better solution.