AnsweredAssumed Answered

Very high Q second-order active filter

Question asked by chevalier on Jun 9, 2015
Latest reply on Jun 12, 2015 by harryh

Hi folks,


I'm in the need for a very high quality factor second-order single-stage active filter. I need a Q of ~5000 !!! The filter is to be used as a readout circuit for some sensor, meaning that one of its surrounding passives will vary according to some external parameter that  we would like to measure, and impact the actual transfer function of the filter.


We are stuck to a single-stage filter because the sensor can not be shared over multiple stages.


The reason for the high-Q is that we would like the phase response to switch very sharply.


Do you think it is realistic to use Sallen-Key or Multiple Feedback filter architecture to achieve such a high Q? I did use the Analog Filter Wizard but I get the following message as soon as I try to increase Q:


The filter you specified has a stage with a Q of 70.6. 

The filter wizard only supports stages with Qs less than 50.


Any comments or tips?