Stable IIR filters-a new design approach

The paper proposes a new approach to designing digital, causal, time-invariant IIR filters approximating arbitrary frequency response. The design task is formulated as an optimisation problem where the cost is a nonlinear function of the tuneable coefficients of the filter´s transfer function. The novelty of the approach lies in the way the stability of the filter is tackled. The cost function comprises a combination of frequency-domain and time-domain components. Frequency-domain components are used to enforce the filter to represent desired complex-valued frequency response, while the time-domain components impose its stability. No equality or nonequality constraints are involved in the optimisation problem related to the proposed method