Novel noise shaping of cascaded sigma-delta modulator for wide bandwidth applications

In this paper, a novel noise shaping of cascaded sigma-delta modulators is proposed. Two stages are incorporated in this sigma-delta modulator. The first stage is realized by a feedforward architecture and the second stage is realized by a low-order single-loop architecture. Unlike the conventional feedforward sigma-delta architecture, we use a 1.5-bit quantizer in the feedback to substitute for the multi-bit DAC to make implementation very easy. However, it is necessary to add error cancellation schemes in the digital part to cancel the coarse quantization errors. By these arrangements, the architecture can reduce the oversampling ratio effectively and the in-band noise can be suppressed significantly to achieve high resolution. Simulation shows this sigma-delta modulator can achieve very good efficiency in wide bandwidth applications