Filter Design Wizard - Douple Pole Low Pass Filters

Problem:
How does a designer implement a double pole low pass filter?

Solution:
Use the schematic below:



The designer, if not familiar with the topics, may want to review Coupling Capacitors (Cin in the schematic) and Virtual Grounding (Vcc/2 in the schematic).

This schematic will produce a unity gain filter only. If gain is desired, it must be accomplished in a separate stage. This filter topology is known as the Multiple Feedback, or MFB. It is a special case of SLOA049A, Appendix A.2.2, where m has been set to 0.5 and n has been set to 4. The MFB toplogy is capable of providing gain as well as low pass filtering, but those calculations are too complex for inclusion in this format. The designer is referred to SLOA049A to implement an MFB low pass filter with gain with a single opamp.