Filter Wiz PRO is powerful and popular CAE application devoted exclusively to the design of active (RC and op amp) filters. ($199 US; $239 with eSketch PRO)

Features:
- design up to order 20 lowpass, highpass, bandpass or bandstop filters
- filters comprised of linear sequence of order 1 or order 2 subcircuits (stages)
- little or no prior expertise required
- incorporates intuitive sequence of design steps that avoid the confusion of menu-based systems
- allows for rapid viewing, comparison and selection of - Approximations and circuit topologies
- provides control over pole-zero pairing, stage sequencing, stage gains and filter sensitivities to changes in component values
- Filter Wiz design files can be imported directly into eSketch, allowing for Monte Carlo Analysis, Parameter Sweep Analysis, merging with other design files, and much more.