A generalised design method for orthogonal IIR lattice filters

The authors investigate the practical problems involved in obtaining signal flow graphs for orthogonal infinite-impulse-response (IIR) filters. A third polynomial derived from the numerator and denominator polynomials of the transfer function is required for such implementations. It is shown that the reflection coefficients of the lattices are extremely sensitive to roundoff errors in this polynomial, and it consequently becomes difficult to implement many IIR filters using orthogonal lattices. The authors assess the transfer functions amenable to lattice realizations and introduce the basis of a CAD (computer-aided design) technique for orthogonal filter design. They show that if more complex structures can be tolerated, then lattice sections can be derived for any general transfer function