Variable IIR Digital Band-Pass and Band-Stop Filters

Abstract

This paper proposes a new method for designing a variable IIR digital band-pass and band-stop filter that has significantly lower implementation and computation complexity compared with some existing methods. The techniques of this method are based on frequency transformation in digital domain when transforming a half-band digital low-pass filter into a digital band-pass and bandstop filter. The principal advantages of this method are that the bandwidth and notch frequency are independently controlled by only two tunable parameters α and β, where the two parameters (α and β) are derived separately from two different first-order all-pass filters; there are fewer coefficient filters, so fewer multipliers and adders are used to implement the circuit, which reduces the cost of design; the method can be applied to all classic filters (e.g., Butterworth, Chebyshev I, Chebyshev II and Elliptic digital filters). This paper also analyzes stable poles varying with α and β of a second-order variable digital Butterworth band-pass and band-stop filter.