Butterworth Active Low Pass Filter Design

I'm designing a low pass active filter with a Butterworth response. The passband is DC to 1.5 kHz, so the -3 dB cut off frequency should be around 2-5 kHz to be safe.

The topology I've decided to use is a second order Sallen-Key, unity gain filter. The schematic can be found below.

I'm a bit confused on how to achieve a Butterworth response, though. From my understanding, the quality factor, Q, has to be 0.707 for a Butterworth response. However, I also read that A = 3 - 1/Q, where A is the gain and Q is the quality factor. With a unity gain topology (A = 1), this would give a quality factor of 0.5. It seems that my understanding of what determines the filter response is wrong.

I also used the coefficients derived from the transfer function of a second order Butterworth filter to design a circuit and simulate it. The circuit simulates well, but at higher frequencies begins to climb again to almost the original value. I used an ideal op amp for the simulation.

How do I choose suitable component values for a Butterworth response? What determines the characteristics of the frequency response? If I have a rough idea of how to achieve a Butterworth response, I can then do some parameter sweeps in my simulation to better understand how they impact the response.

• try giving your supply voltage a ground connection at its midpoint. Commented Dec 29, 2021 at 17:13
• RM429 - Hi, It seems you deleted the question immediately after it received an answer, but that's not how things are done here. Stack Exchange collects the Q&A for people to refer to in future, and questions with useful answers don't (usually) get deleted, so the topic has been undeleted. If you have questions about this, you can ask on Electrical Engineering Meta. Thanks. (Also, since your comment suggests the answer was useful, you can upvote and optionally accept it.) Commented Dec 29, 2021 at 17:32
• RM429 are we done here now? Is there anything else that needs advice on this circuit? Commented Dec 30, 2021 at 11:21