High-order single-loop double-sampling sigma-delta modulator topologies for broadband applications

This paper presents novel low-voltage high order single loop sigma-delta modulator structures for wideband applications. The proposed architectures employ the technique of double-sampling to double the effective oversampling ratio (OSR) without increasing the sampling frequency. To alleviate the quantization noise folding into the inband frequency region which is a result of the mismatch between the sampling capacitors of the feedback´s digital-to-analog converter (DAC) paths, a zero is placed at the half of the sampling frequency of the modulator´s noise transfer function (NTF). The problem of this additional zero in the NTF is solved through the proposed modulator architectures with a very simple design procedure.