FilterPro Multiple Feedback (MFB) and Sallen-Key Design Program is a Windows application. This application designs MFB and Sallen-Key low-pass and high-pass filters using Voltage Feedback Op Amps, Resistors and capacitors. It also supports a fully-differential version of the MFB circuit. This program includes Bessell, Butterworth, Chebychev, and linear phase filter types and can be used to design filters from 1 to 10 poles. The capacitor values in each stage can be either selected by the computer or entered by the designer. An "always on" prompt window provides context-sensitive help information to the user. The response of The Filter is displayed on a graph, showing gain, phase and group delay over Frequency.
A new version of FilterPro is now available, Version 2.0, that includes band-pass, notch, wide-band-pass, and band-reject circuits.
The FilterPro V2.0 band-pass circuit is based on the MFB circuit. Because the band-pass filter is most often used for tone detection and high Q filters usually need high gain, a method was found to make the gain equal to the Q of the filter. When this is done the sensitivity to variation of the passive components is reduced allowing for a more reproducible filter.
The FilterPro V2.0 notch circuit is a dual amplifier circuit whose sensitivity to variation of passive components is also reduced compared to the traditional twin-T circuit. This filter is often used to block specific tones such as 60 Hz, 120 Hz, 1kHz, etc.
The FilterPro V2.0 wide-band-pass filter uses a high-pass filter cascaded with a low-pass filter. This is very useful for band-pass filters with a Q of less than 1 because the passband response is easily made flat and because the filter types such as Bessell, Butterworth, etc. are used.