A Simple Structure for MASH Modulators with Highly Reduced In-Band Quantization Noise

摘要

A new topology of multi-loop sigma-delta modulators is proposed which utilizes two analog inter-stage paths to improve the noise-shaping ability of the modulator by one order and simultaneously optimizing one pair of noise transfer function zeros. Furthermore, an improved version of this modulator is presented which is simpler to implement. So, by using minimum extra circuit and without increasing the number of active blocks, the in-band quantization noise is significantly reduced, and hence, the modulator signal-to-noise and distortion ratio (SNDR) is highly increased. As an example, a multistage noise-shaping (MASH) 2-1 modulator based on the improved proposed structure is more examined. Some implementation considerations including the timing issue and first-stage quantization noise extraction are verified. Theoretical analysis and simulation results in both system and circuit levels are presented to confirm the usefulness of the proposed structure. The modulator is implemented in a 90-nm CMOS technology using Spectre-RF. For 10 MHz signal bandwidth, 85.2 dB SNDR and 87 dB dynamic range are achieved, while the power consumption is 31.6 mW from a single 1 V power supply.