Delta operator realizations of IIR filters have recently received a lot of interest due to their good finite-wordlength properties.Here we present a detailed analysis of the computationally efficient transposed direct form I1 delta structure, which is also known to have excellent roundoff noise performance under fast sampling. Focus is on the roundoff noise minimization in fixedpoint implementations. The free A parameter in the delta operator is optimized with respect to the output roundoff noise within the scaling constraints. Moreover, required internal wordlength to obtain prespecified noise performance is derived.