Abstract: This paper reviews the exact and approximate linear phase IIR filter designs based on the classical approximating functions (elliptic, Butterworth and Chebyshev type functions) and the usage of various processing techniques. Using allpass IIR subfilters obtained from the minimal phase solution, it is possible to implement a causal filter which exhibits simultaneously an approximate constant amplitude response and an exact or approximate linear phase response.
Key words: Linear phase filters, IIR filters, allpass filters, FIR filters, noncausal filters.