High-order tunable passive digital filters

In this paper, high-order tunable low-pass, high-pass, band-pass, and band-stop passive digital filters for realtime sharp cutoff filtering applications is introduced. An analytical expression for each of the coefficients of the first-order and the second-order passive digital filter sections after low-pass to low-pass/high-pass frequency transformation has been derived. For the low-pass to band-pass/band-stop frequency transformation, an analytical expression for each of the coefficients of the second-order and the decomposed second-order passive digital filter sections has also been derived. These analytical expressions facilitate the real-time computation of all the required filter coefficients, from any specified new cutoff frequency for the low-pass/high-pass case, and from any specified new center frequency and/or new bandwidth for the band-pass/band-stop case.