state variable filter design

FilterPro V3.0 does not support state-variable active filter topologies, currently. We have found that in most cases users want to use a minimum component topology such as the Multiple-feedback MFB), or Sallen-key (SK). The state-variable filters require multiple operational-amplifiers and most engineers tend to shy away from them. We do have plans to include some low-sensitivity, multiple-amplifier topologies, in the next revision of FilterPro, but we haven’t decided exactly what topologies they will be. We just finished a complete top-to-bottom rebuild of FilterPro and it was just too much to try and get into this new revision in any kind of reasonable time frame.

 If you really need to use State Variable topologies, there is a relatively low-cost filter synthesis program available called Filter Wiz Pro. It is available from Schematica software:


I use this program often and it does include some state-variable topologies; KHN, Tow-Thomas, etc. However, I haven’t played with these topologies much so I can’t tell you if they provide all the flexibility you are seeking. They do offer a free download and you should be able to determine if it does everything you need.


TI does offer a universal active filter product, UAF42, which is a state-variable filter. The gain and filter response characteristics can all be set via a few resistors. We do have a filter synthesis program for the UAF42 that calculates the component values based on your gain, Q, fc, etc, inputs. Here’s where you can find the data-sheet:

 And the UAF42 software: