Digital Filter Designer's Handbook: With C++ Algorithms: Rorabaugh, C. Britton: 9780070538061: Amazon.com: Books
Butterworth filter - Wikipedia
Tutorial on Filters in Control Systems | Control Notes
Filter Design for Signal Processing Using MATLAB and Mathematica: Lutovac, Miroslav D, Tosic, Dejan V., Evans, Brian L.: 9780201361308: Amazon.com: Books