LIMIT-CYCLE-ABSENT ALLPASS FILTER LATTICE STRUCTURE

A lattice-based second-order allpass filter (200) providing a digital filter, absent of limit cycles, includes interconnected quantizers(214, 224), delays (232, 240), multipliers (210, 220), and adders (208, 216, 228) for defining a transfer function, where the circuit corresponds in order and values to intrinsic values of the transfer function. The quantizers are connected in series after the multipliers to eliminate any double precision additions which give rise to the appearance of parasitic oscillations. The savings in hardware results from locating the quantizers after the multipliers; thus, eliminating all double precision additions that are mandatory in the classical second-order lattice structure. The second-order allpass filter coefficients that retain the limit-cycle-absent property of the filter correspond to specific guidelines.