A 113.7 dB SINAD, 18.59 Bit ΣΔ Modulator for High-Resolution ECG Recordings
Received: 11 July 2025 | Revised: 29 July 2025, 4 August 2025, and 18 August 2025 | Accepted: 22 August 2025 | Online: 8 September 2025
Corresponding author: M. Kavitha
Abstract
High-Resolution Electrocardiograms (HRECGs) are essential to detect low-amplitude signals in the ventricles known as "Late Potentials" that cannot be detected with a standard ECG. This work presents the design of a fully-differential second-order Cascade-of-Integrators with Feedforward (CIFF) one-bit Continuous-Time (CT) ΣΔ modulator for HRECG recordings. The modulator incorporates two active RC loop filters, a summer, and a StrongARM latch, along with a single-bit resistive DAC. Integrator and summer circuits are designed using a differential operational transconductance amplifier (DOTA). The area of the pMOS input transistors in the first-stage integrator is increased compared to that of the second-stage integrator and summer to reduce flicker noise. The StrongARM latch is implemented without using a preamplifier, leading to a reduction in area and power dissipation. The designed ΣΔ Modulator (ΣΔΜ) circuit achieves a high Signal-to-Noise And Distortion ratio (SINAD) and resolution through an optimal design approach and a higher oversampling ratio (OSR). The proposed ΣΔM architecture is implemented using the MATLAB delta-sigma toolbox at the system-level and the Cadence Virtuoso EDA tool at 0.18µm CMOS technology at the circuit-level. The simulated performance parameters are validated at behavioral, macromodel, and circuit levels. To measure ECG signals of 150Hz bandwidth, a 300 kHz sampling frequency ( ) is used, resulting in an OSR of 1000. The proposed design achieves a SINAD of 113.7dB and a resolution of 18.59 bits. The modulator's measured power consumption is 0.49mW, achieving Schreier's Figure-of-Merit (FoM) of 168.55 dB, occupying an active area of 0.582 mm2.
Keywords:
continuous-time sigma-delta modulator, quantizer, operational transconductance amplifier, DACDownloads
References
"Non communicable diseases," World Health Organization, Dec. 23, 2024. https://www.who.int/news-room/fact-sheets/detail/noncommunicable-diseases.
S. Narayanaswamy, "High Resolution Electrocardiography," Indian Pacing and Electrophysiology Journal, vol. 2, no. 2, pp. 50–56, Apr. 2002.
A. Giorgio, M. Rizzi, and C. Guaragnella, "Efficient Detection of Ventricular Late Potentials on ECG Signals Based on Wavelet Denoising and SVM Classification," Information, vol. 10, no. 11, Nov. 2019, Art. no. 328.
A. Kosari, J. Breiholz, N. Liu, B. H. Calhoun, and D. D. Wentzloff, "A 0.5 V 68 nW ECG Monitoring Analog Front-End for Arrhythmia Diagnosis," Journal of Low Power Electronics and Applications, vol. 8, no. 3, Sep. 2018, Art. no. 27.
S. Y. Lee, J. H. Hong, C. H. Hsieh, M. C. Liang, S. Y. Chang Chien, and K. H. Lin, "Low-Power Wireless ECG Acquisition and Classification System for Body Sensor Networks," IEEE Journal of Biomedical and Health Informatics, vol. 19, no. 1, pp. 236–246, Jan. 2015.
S. Y. Lee, P. H. Su, K. L. Huang, Y. W. Hung, and J. Y. Chen, "High-Pass Sigma–Delta Modulator With Techniques of Operational Amplifier Sharing and Programmable Feedforward Coefficients for ECG Signal Acquisition," IEEE Transactions on Biomedical Circuits and Systems, vol. 15, no. 3, pp. 443–453, Jun. 2021.
R. Zanbaghi, T. S. Fiez, and G. Temes, "An op-amp sharing technique for continuous-time ΔΣ modulators," in 2010 53rd IEEE International Midwest Symposium on Circuits and Systems, Seattle, WA, USA, Aug. 2010, pp. 592–595.
Z. Li and T. S. Fiez, "A 14 Bit Continuous-Time Delta-Sigma A/D Modulator With 2.5 MHz Signal Bandwidth," IEEE Journal of Solid-State Circuits, vol. 42, no. 9, pp. 1873–1883, Sep. 2007.
J. Liang, S. W. Sin, U. Seng-Pan, F. Maloberti, R. P. Martins, and H. Jiang, "A High DR High-Input-Impedance Programmable-Gain ECG Acquisition Interface with Non-inverting Continuous Time Sigma-Delta Modulator," in 2019 IEEE Asian Solid-State Circuits Conference (A-SSCC), Macau, Macao, Nov. 2019, pp. 309–312.
F. Hemmati and E. Ν. Aghdam, "A low-power CT 2nd order Delta Sigma modulator using a new design methodology for biomedical applications," AEU - International Journal of Electronics and Communications, vol. 137, Jul. 2021, Art. no. 153779.
M. Kavitha, S. Akhila, and A. Kannan, "Flexible Analog Front End Architecture for Biomedical Applications," in 2021 IEEE 3rd PhD Colloquium on Ethically Driven Innovation and Technology for Society (PhD EDITS), Bangalore, India, Nov. 2021, pp. 1–2.
M. Kavitha, S. Akhila, and A. Kannan, "Design and Implementation of a Second Order Continuous-Time ΣΔ Modulator for ECG Signal Acquisition," Engineering, Technology & Applied Science Research, vol. 13, no. 1, pp. 10128–10133, Feb. 2023.
S. Pavan, N. Krishnapura, R. Pandarinathan, and P. Sankar, "A Power Optimized Continuous-Time ΔΣ ADC for Audio Applications," IEEE Journal of Solid-State Circuits, vol. 43, no. 2, pp. 351–360, Oct. 2008.
R. Schreier, S. Pavan, and G. C. Temes, Understanding Delta‐Sigma Data Converters, 1st ed. Wiley, 2017.
D. Basak and K. P. Pun, "Gm-cell nonlinearity compensation technique using single-bit quantiser and FIR DAC in Gm-C based delta-sigma modulators," in 2016 IEEE International Symposium on Circuits and Systems (ISCAS), Montréal, QC, Canada, May 2016, pp. 1510–1513.
S. Pavan, R. Schreier, and G. C. Temes, Understanding Delta-Sigma Data Converters. John Wiley & Sons, 2017.
R. R. Harrison and C. Charles, "A low-power low-noise CMOS amplifier for neural recording applications," IEEE Journal of Solid-State Circuits, vol. 38, no. 6, pp. 958–965, Jun. 2003.
J. Kim, Q. Duan, J. Choi, C. Song, and J. Roh, "A 2.16-μW Low-Power Continuous-Time Delta–Sigma Modulator With Improved-Linearity Gₘ for Wearable ECG Application," IEEE Transactions on Circuits and Systems II: Express Briefs, vol. 69, no. 11, pp. 4223–4227, Aug. 2022.
Q. Lin et al., "A 119dB Dynamic Range Charge Counting Light-to-Digital Converter For Wearable PPG/NIRS Monitoring Applications," IEEE Transactions on Biomedical Circuits and Systems, vol. 14, no. 4, pp. 800–810, Dec. 2020.
D. Akhila, "Analysis and Design of OTA topologies for Bio-Potential signals," International Journal of Future Generation Communication and Networking, vol. 14, no. 1, pp. 557–568, Feb. 2021.
J. Zhang, H. Zhang, Q. Sun, and R. Zhang, "A Low-Noise, Low-Power Amplifier With Current-Reused OTA for ECG Recordings," IEEE Transactions on Biomedical Circuits and Systems, vol. 12, no. 3, pp. 700–708, Jun. 2018.
A. Mesri, J. Javidan, and M. Mahdipour Pirbazari, "Analysis and design of a two-stage amplifier with enhanced performance," Microelectronics Journal, vol. 46, no. 12, Part A, pp. 1304–1312, Dec. 2015.
B. Razavi, "The StrongARM Latch [A Circuit for All Seasons]," IEEE Solid-State Circuits Magazine, vol. 7, no. 2, pp. 12–17, 2015.
B. Razavi, "The Design of a Comparator [The Analog Mind]," IEEE Solid-State Circuits Magazine, vol. 12, no. 4, pp. 8–14, 2020.
J. L. A. de Melo, N. Paulino, and J. Goes, "Continuous-Time Delta-Sigma Modulators Based on Passive RC Integrators," IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 65, no. 11, pp. 3662–3674, Aug. 2018.
J. Basu and P. Mandal, "Delta-sigma modulator based compact sensor signal acquisition front-end system," Microelectronics Journal, vol. 98, Apr. 2020, Art. no. 104732.
V. Sharma, N. Kumar Y.B., and V. M.h., "67 dB SNDR 20 kHz BW SC third-order ΣΔ modulator with single Op-Amp and 20 µW power consumption for bio-medical applications," IET Circuits, Devices & Systems, vol. 14, no. 6, pp. 881–891, 2020.
Y. Li, H. Li, T. Qu, Q. Liu, Z. Hong, and J. Xu, "A 101-dB DR 2.2GΩ-Input-Impedance Direct Digitization ExG Front-End With Δ-Modulation," IEEE Transactions on Biomedical Circuits and Systems, pp. 1–10, 2025.
Downloads
How to Cite
License
Copyright (c) 2025 M. Kavitha, S. Akhila, Anand Kannan
This work is licensed under a Creative Commons Attribution 4.0 International License.
Authors who publish with this journal agree to the following terms:
- Authors retain the copyright and grant the journal the right of first publication with the work simultaneously licensed under a Creative Commons Attribution License that allows others to share the work with an acknowledgement of the work's authorship and initial publication in this journal.
- Authors are able to enter into separate, additional contractual arrangements for the non-exclusive distribution of the journal's published version of the work (e.g., post it to an institutional repository or publish it in a book), with an acknowledgement of its initial publication in this journal.
- Authors are permitted and encouraged to post their work online (e.g., in institutional repositories or on their website) after its publication in ETASR with an acknowledgement of its initial publication in this journal.
