I've been reading through the LTC1264-High Speed Quad Universal Filter Building Block datasheet but I'm having some trouble deciphering the meaning of some of the variables used in the equations for the different modes of operation. For example, in the image below I have highlighted the variables fi, f0, and fn in the equations that govern the Mode 1b topology. Unfortunately, Linear Technology does not include a "Definition of Terms" anywhere in the datasheet (seems kind of silly).
Can anyone tell me what these three variables are? My assumption is that f0 is the center frequency of the filter but I don't have a clue about the other two values. To make things more confusing, later in the datasheet in the "Guide to Bandpass Design" on page 11 these equations are shown:
These equations are for the same circuit in the 1b mode. What then is fcenter and why does it not appear int the equations in the previous image?