Continuous-time (CT) SD modulators are growing increasingly popular in wideband A/D conversion. Such applications require high orders of quantisation noise shaping and multi-bit quantisers, to compensate for the resulting low oversampling ratios. These, however, add circuit complexities and excess loop delay that are detrimental to the modulator control loop. A CT SD modulator can potentially achieve a higher performance with a lower bandwidth requirement than its discrete-time (DT) counterpart. Unfortunately, CT SD modulators suffer from problems not seen in dependent jitter and non-rectangular DAC pulse shapes. Low-oversampling CT SD modulators are also sensitive to a low bandwidth in the input stage of the forward filter. These effects are often tackled by a modification ion the CT SD modulator architecture. Unfortunately, the resulting CT SD modulator control loop is often suboptimal and sensitive to changes in the modulator coefficients. In this thesis, a design-by-optimisation method is proposed to find the optimum that satisfies the constraints set by the implementation of the CT SD modulator, its feasibility and any other additional design criteria. Robustness in the final design is ensured by optimising directly on the coefficients of the CT SD modulator, and evaluating the stability and the performance of its DT equivalent model. The DT equivalent is computed using a numerical implementation of the impulse-invariance technique. This implementation can deal with both excess loop delay and non-rectangular DAC pulse shapes, numerically and in general form. This is, to the best of the author’s knowledge, the first implementation of its kind. It is shown that for a low value of loop delay, a resonator based forward filter is optimum, while, contrary to assumptions made in the literature, real poles in the forward filter are preferable for moderate values of loop delay. It is hoped that the bandwidth requirement of CT modulators can be minimised in a similar manner. A numerical curve fitting approach is also presented that models many of the nonidealities in an integrator circuit response with a low-order model transfer function.