I designed a unity gain low pass Sallen key filter with equal resistor values of 10k and capacitors of 8nF. The cut-off frequency to my knowledge at the -3dB point is defined as:
\$f=\frac{1}{2\pi\sqrt{R1R2C1C2}}\$
Upon simulation the cut-off designed for, which is 2kHz is at the -6dB point. Is this formula defined for the -6dB point since this is a second order system? I'm confused.
Circuit:
Frequency Response:
Cut-off is at -6dB.