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An Ultra-Low-Voltage VCO-Based ΔΣ Modulator Using Self-compensated Current Reference for Variation Tolerance

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Abstract

This paper introduces a voltage-controlled-oscillator-based (VCO-based) first-order delta-sigma (ΔΣ) modulator that uses a novel current reference to improve the robustness of the modulator at ultra-low operating voltages. The proposed current reference harnesses the difference in transistor characteristics between weak inversion and moderate inversion to generate residue voltage, which is a function of process and temperature variations. The current generated by the proposed reference is used to bias a fully differential VCO integrator and a feedback current digital-to-analog conversion in the delta-sigma modulator for variation tolerance. Test chips designed and fabricated in 65-nm CMOS technology operate successfully at 0.3 V and achieve SNDR of 56.1 dB across 10 kHz bandwidth while consuming only 510 nW of power. This corresponds to a state-of-the-art figure of merit of 49 fJ/conv.-step. Measurement results for the proposed current reference and the modulator also demonstrate 3 × and 20 × improvement in process and temperature variation tolerance, respectively, while operating at such low voltages.

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Data Availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Funding

The research of the project was supported by Ministry of Education, Singapore, under Grant AcRF TIER 1- 2018-T1-002-105 (RG 174/18).

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Authors and Affiliations

  1. A*STAR Institute of Microelectronics, 2 Fusionopolis Way, #08-02 Innovis, Singapore, 138634, Singapore

    Neelakantan Narasimman

  2. Centre for Integrated Circuits and Systems, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798, Singapore

    Tony Tae-Hyoung Kim

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  1. Neelakantan Narasimman
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Correspondence to Tony Tae-Hyoung Kim.

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Narasimman, N., Kim, T.TH. An Ultra-Low-Voltage VCO-Based ΔΣ Modulator Using Self-compensated Current Reference for Variation Tolerance. Circuits Syst Signal Process 40, 1089–1110 (2021). https://doi.org/10.1007/s00034-020-01523-6

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