Approximation of classical IIR filters with additional specifications

In this a paper, we introduce a modified tapped all-pass (MTA) structure for the sum of two all-pass functions. The new structure includes linear coefficients in the all-pass sections, allowing additional constraints such as null or group delay constraints for the filters. These null constraints are significant for applications when the suppression of the noise at certain frequencies is important. An alternative structure to incorporate the extra constraints is the modified tapped cascade (MTC) infinite impulse response structure. Design examples show that the MTA structure is less sensitive to quantization than the MTC structure in the passband. Moreover, the total number of multiplications is significantly reduced by using the MTA structure as compared to the MTC structure.