If you have an unused op-amp stage anywhere, you can buffer this “virtual ground” as well. Active highpasses just aren’t as useful as lowpasses. Highpass filters really shine in radio ...

From the 1970s however, dual and quad op amps became popular, largely aimed at designers of active filters. Duals and quads are widely available today; a few triple op amp chips are produced as ...

Fundamentals of analog filter design and linear circuits are covered in a book and kit of parts that are available on EIM ...