Microchip FilterLab® Software
Microchip FilterLab® is an innovative software tool that simplifies active filter design that consists of resistors, capacitors, and op-amps. It generates the frequency response and the circuit as well as the SPICE model of the designed filter. It is available at no cost at Microchip's FilterLab® website.
The FilterLab® 2.0 User's Manual can be downloaded here.