DELTA-OPERATOR REALIZATIONS OF DIRECT-FORM IIR FILTERS

The use of the delta operator in the realizations of digital filters h as recently gained interest due to its good finite-word-length perform ance under fast sampling, We studied efficient direct form structures, and show that only some of them can be used in delta configurations, while others are evidently unstable, In this paper, we focus on the ro undoff noise analysis, Of all the direct-form structures, the direct f orm II transposed (DFIIt) delta structure has the lowest quantization noise level at its output, This structure outperforms both the convent ional direct-form (delay) structures, as well as the state-space struc tures for narrow-band low-pass filters with respect to output roundoff noise, Excellent roundoff noise performance is achieved at the cost o f only a minor additional implementation complexity when compared with the corresponding delay realization, Complexity of a signal processor implementation of the DFIIt delta structure, which was found to be th e most suitable delta structure for signal processors, is compared wit h those of the direct form and state-space delay structures, In additi on, some hardware implementation aspects are discussed, including the minimization of the internal word length.