There are few inconsistencies in the "BAND-PASS KRC OR SALLEN-KEY FILTER " section on page 21, Rev. G of this datasheet: http://www.analog.com/media/en/technical-documentation/data-sheets/OP1177_2177_4177.pdf
Formula (3): Q = K * sqrt(R1 / R2) is inverted with the formula mentioned later on: " For Q = 1 / sqrt(2), R1/R2 = 2 in the circuit example. "
Also, the later formula suggests " Select R1 = 5 kΩ and R2 = 10 kΩ for simplicity. " , but, those values do not produce "R1/R2 = 2". And In the schematic R1 = 20 kΩ and R2 = 10 kΩ.
There's another error in corner frequency for the second stage. The formula should be: Fc = 1 / (2 * pi * R * sqrt(C3 * C4)) instead of the existing version with C3 / C4, which cancels the capacitance units.
Thanks for bringing this to our attention. There seems to be some errors in this datasheet's calculations for Q that we need to fix.
In the meantime, how can we can help solve your filtering problem? Have you taken a look at our Filter Wizard program?
Thanks Matt. No pending filtering issues. Good suggestion on the Filter Wizard tool.