smarty wrote on Jun 19th, 2009, 2:25am:........But my understanding was, gm-C would suffer from linearity perspective( which is one of the important criteria for filter) than the other counterpart, then in that case why is gm-C preferred, for sure people suggest that for high frequency ( I assume the other poles of op-amps) could affect the filter performance.
...... Say we have a specs for Cut-off frequency, dynamic range, noise specs, group delay specs ( just to name a few) .......
Should I go from books for any approximation( butterworth, bassel, chebeshev...) or any other way.
At first, You are right in saying that dynamic properties/linearity are other aspects I forgot to mention.
At second, my understanding of your question now is that you are not sure about the several steps in designing a filter.
Therefore, at first the approximation has to be selected - and this depends on your damping requirements expressed by frequencies and corresponding damping.
Here you have several alternatives e.g. with or without zeros. On the other hand, this choice influences also the filter degree which is required - and also the delay characteristics (if they play a role). You see, it ends in a compromize between several conflicting aspects.
But thatīs normal live for analog engineers and makes a single and final answer to your question difficult.
Regards
buddypoor