Article ADIsimPE Sallen key low pass filter Bode plot

Original Question: ADIsimPE Sallen key low pass filter Bode plot by nishnt

I was trying to simulate the Bode plot for a Sallen Key low pass filter (R= 10k , C= 1nF) . The filter was designed for a cut off frequency of 15.9 kHz.  The simulated filter response however shows a 3db frequency of 10 kHz .

Could any one help explain why the simulated frequency response is not as expected and what I am likely doing wrong ?.

I have attached the schematic and the response obtained.

4278.attachments.zip

Verified Answer: RE: ADIsimPE Sallen key low pass filter Bode plot by nishnt

Answering my own question here. The 3 db point for this case is sqrt(sqrt(2) -1) / (2*pi*R*C)     which works out to 10 kHz.  The simulation is correct.  fc in this case is not the 3 db frequency but called the natural frequency.

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