Design of perfect reconstruction QMF lattice with signed powers-of-two coefficients using CORDIC algorithm
The lattice structure has several advantages over the tapped delay line form, especially for the hardware implementation of general digital filters. It is also efficient for the implementation of quadrature mirror filters (QMF), because the perfect reconstruction (PR) is conserved even under the severe coefficient quantization. Moreover, if lattice coefficients are implemented by signed powers-of-two (SPT), the hardware complexity can also be reduced. But the discrete space represented by the SPT is sparse when the number of non-zero bits is small. This paper proposes an orthogonal QMF lattice with SPT coefficients that can provide much denser discrete coefficient space than the conventional structure. For this purpose, we employ the CORDIC algorithm that is structurally related to the PR lattice filter with SPT coefficients. The paraunitariness of CORDIC subrotation also continues to hold the PR condition to our wishes. Since the proposed architecture provides denser coefficient space, it shows less coefficient quantization error than the conventional QMF lattice.