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

作者：Tamaddon Mohsen; Yavari Mohammad^*

来源：Analog Integrated Circuits and Signal Processing, 2015, 85(2): 283-297.

DOI：10.1007/s10470-015-0562-7

• Asynchronous pulse width modulator
• Continuous-time sigma-delta modulators
• Noise-coupling
• Time-to-digital converter

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.

• 出版日期2015-11