ABSTRACT
This chapter begins by explaining the procedure of scaling, which focuses on designing a particular type of filter in normalized form. It explains the nature of Butterworth filters and gives examples of the design of such filters. The chapter introduces first-order active filters and analyses their responses. It presents second-order active filters of various types, using a single op amp in the noninverting or inverting configuration. Butterworth filters characteristically have a maximally flat response in the passband, which makes them particularly useful as low-pass and high-pass filters. Active filters are commonly used, because the op amp provides many advantages, including the convenience of using only capacitors and resistors, with a Q that is not limited to 0.5 or less, as is the case with passive resistor–capacitor circuits. The chapter ends with a discussion of a second-order universal active filter that can implement any of the second-order responses.
