With the AktivFilter 2.4 of SoftwareDidaktik you can design active filters which are tuned to the operational amplifier. So a manual adjustment of the designed filter circuit becomes superfluous with it. AktivFilter is a powerful software for the design of active bandpass filters, highpass filters, lowpass filters and bandreject filters with operational amplifiers. The special feature of this program is the ability of co-ordinating the component values of the filter circuit with the type of operational amplifier and with the standard series (E12, E24, E48 or E96) of the component values. Thus a later adjustment of the built circuit becomes unnecessary. For many applications AktivFilter enables you to use inexpensive opamp types instead of expensive ones. Developers of audio electronics, e.g. studio and high end equipment, can also profit from AktivFilter, as this program supports some high-quality audio opamps.source

QuickFil is a software for designing passive electronic filters. The result is an optimized circuit of inductors (L) and capacitors (C).You can use this software to design the filter circuits for:
Types of filters:

• Lowpass
• Highpass
• Bandpass
• Bandstop
• Allpass
• Asymmetric bandpass filters
• Parametric bandpass filters

Approximations:

• Butterworth (maximally-flat filters)
• Chebyshev (equal-ripple filter)
• Inverse Chebyshev
• Elliptic (Cauer)
• Bessel (maximally flat delay)
• Modified Bessel
• General Equal-ripple approximation
• General maximum-flat approximation

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Filter Wiz PRO active filter designer version 4 has just been released. Version 4 represents a major advance in the rapid design of stable and effective active filters.

features:

• completely new interface
  - allows instant access to all completed phases of the filter design, and presents information and choices with clarity and ease of use
• built-in simulator
  - provides eSketch-like simulation of the filter design, including effects of op amp Gain BandWidth. The user can preview the gain response when selecting circuits for each stage. And now Filter Wiz PRO can export eSketch .ES1 files, providing two ways of transferring data from Filter Wiz PRO to eSketch PRO
• up to 21 Approximations available
  - choose from 10 “standard” Approximations, plus 5 linear phase Approximations, and 6 Low-Q Approximations that are extremely useful for augmenting filter stability
• more circuit topologies
  - includes new topologies (circuits), and many variations of existing topologies, including voltage divider inputs to better meet optimal stage gain requirements
• more selection aids
  - in addition to stage gain simulation, view indicators of stage Noise (resistor noise), GBW requirement, and Gain Spread. Also view design windows showing Input Impedance (vs frequency), Passive Sensitivity, Active Sensitivity, Dynamic Range, and Tuning instructions
• Monte Carlo analysis
  - simulate gain spread due to inexact component values, with a choice of 3 probability distributions – Uniform, Gaussian and Worst Case
• Temperature Effect analysis
  - determine response change due to environmental temperature rise and component temperature coefficients
• “Strategy” help windows
  - view help topics appropriate to each design phase, accessible through “Strategy” buttons. All help topics are also available through a standard help file

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Westbay Compufilt, first introduced in 1994, has been fully updated for V2.0, with the introduction of many new features. The principle of Compufilt is to provide ready built models of Feedthrough, Mains (Line), and PCB filters, to allow insertion loss versus frequency characteristics to be plotted. A range of pulse shapes can also be applied to filter circuits, allowing behaviour in data circuits and to transient events to be modelled. A fully-featured Search Wizard is also available to provide a filter circuit and component values to match particular performance requirements.This is a free of charge program that can be copied and installed as required. It provides unlimited modelling of Feedthrough Capacitors, and unlimited access to the URL Database and Web Browser. All other circuit models can also be accessed, with restrictions on source and load circuits and component values.source