Noise shaping is one of the distinguishing characteristics of the sigma-delta modulation technique that separates it from other types of pulse-width modulation schemes. In sigma-delta modulation, unwanted noise and harmonics caused by quantization are intentionally pushed toward the high-frequency band in order to achieve high resolution data conversion within the signal bandwidth. Due to its robust, high in-band linearity, the sigma-delta modulation technique finds numerous applications in industry. Generally speaking, as the order of a sigma-delta modulator increases, the modulator performance becomes better, which unfortunately comes along with a decrease in the modulator¡¦s stable input range. This thesis presents a novel adaptive law which is capable of on-line tuning the loop filter of a sigma-delta modulator and reducing the out of band gain of the resulting noise transfer function when the modulator input is large, thereby widening the stable input range of the modulator without significant sacrifice of the performance. The simulation and experimental results prove the effectiveness of the proposed adaptive sigma-delta modulator.

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