High-order single-stage single-bit oversampling A/D converter stabilized with local feedback loops

A new method for the stabilization of high-order (>2) single-stage single-bit oversampling A/D converters is proposed. In this approach, the stability of the modulator is achieved by preventing any unbounded increase in the internal node-voltages through the insertion of local feedback signals inside the modulator loop. Local feedback loops prevent individual integrators from saturating and keep the output voltages within the proper bounds. The error caused by the local feedback signals is cancelled by feeding these signals through a digital correction path. Since the frequency of overloading can be made very low by proper design, the effect of imperfect cancellation due to mismatches in the two signal paths caused by the modulator nonidealities is quite small. Hence, compared to the MASH architectures, the proposed approach achieves stability with lower sensitivity to finite op amp gain, an advantage in the modern low power/low voltage technologies