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An NTF-enhanced time-based continuous-time sigma-delta modulator

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Abstract

Translation of the amplitude axis to the time axis can be a promising approach to alleviate the analog-to-digital converter’s resolution problems in low-voltage CMOS circuits. From this point of view, a noise-coupled time-based continuous-time sigma-delta modulator (TCSDM) based on the asynchronous pulse width modulator (APWM) and the time-to-digital converter (TDC) is presented. Noise-coupling is realized by extracting the time quantization error of the TDC and injecting its delayed version to the input of the APWM. By using a novel implementation of the noise-coupling technique in the proposed TCSDM, the modulator’s noise-shaping order is improved by one. Unlike the conventional noise-coupled sigma-delta modulators, in the proposed structure, the need of an extra subtractor at the quantizer input is resolved through merging the excess loop delay compensation path with the proposed noise-coupling branch. Comparative analytical calculations and behavioral simulation results are presented to verify the performance of the proposed time-based modulator. To confirm the validity of the proposed structure, the effects of main circuit non-idealities in the modulator’s performance are taken into consideration and the related simulation results are investigated. A digital-friendly implementation of the quantizer in the proposed modulator makes it suitable for low-voltage nanometer CMOS technologies.

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Authors and Affiliations

  1. Integrated Circuits Design Laboratory, Department of Electrical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran

    Mohsen Tamaddon & Mohammad Yavari

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  1. Mohsen Tamaddon
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  2. Mohammad Yavari
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Correspondence to Mohammad Yavari.

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Tamaddon, M., Yavari, M. An NTF-enhanced time-based continuous-time sigma-delta modulator. Analog Integr Circ Sig Process 85, 283–297 (2015). https://doi.org/10.1007/s10470-015-0562-7

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  • DOI: https://doi.org/10.1007/s10470-015-0562-7

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