WEBENCH® Tools/FILTERPRO: Filter Design based on fully differential amplifier

Hello Shota,

TI's new Filter Design Tool is a beta version, and it doesn't appear to include the fully differential amplifier (FDA) active filter topologies just yet. I believe the group building the new program intends to include the FDA versions as the program progresses.

TI's older FilterPro program did include the FDA versions and it is still very usable for their synthesis. I found a Google link to FilterPro and it appears to provide the program download capability.

The FilterPro program can be found here (the download button is a little further down the webpage):

If you are able to get FilterPro downloaded and running, go through the design steps until you reach step 4. Select the "Multiple Feedback (fully differential)" option, and proceed with the remainder of the filter design from there.

Note there is an error in the FDA filter circuit schematics shown in FilterPro. The schematics show the two FDA outputs shorted together. Remove the wire connected between the two FDA outputs in the actual circuit. If the short is not removed between the FDA outputs active filters will not work correctly.

If you wish to take a more organic approach to designing FDA active filters see my article in the 3Q 2009 Analog Applications Journal:

Regards, Thomas

Precision Amplifiers Applications Engineering