If you can find it in the library somewhere (out of print, though i have a copy) the burr brow Operational Amplifiers Design and Applications book is very good, taking you through the basics to even more advanced things, off the top of my head you would want to look at chapter 8, round abouts page 280 i want to say, i hope you can find the book, it was one of my favorite when i had analog design courses and when i was doing research on macromodeling. If you have a specific filter applications, post and maybe i can help.