Sallen-Key Band-Pass Filter
Sallen–Key topology filters are second-order active filters whose simplicity makes them a popular choice for general filtering applications. In this Demonstration, Bode plots are produced for single-stage low-pass and high-pass filters or a combination of these filters, up to 10 stages each.
The transfer function, cutoff frequency, and for low-pass and high-pass filters (with non-unity gain) are
where and , , , , , are the resistances and capacitances.
For higher-order filters, the transfer funtions 1 and 2 are raised to the order of the filter. For a high-pass (low-pass) filter, set the order of the low-pass (high-pass) filter to "0".
 "Analysis of the Sallen–Key Architecture." Texas Instruments. (Sep 2002) http://www.ti.com/lit/an/sloa024b/sloa024b.pdf.