Abstract
This study proposes the design of a light to digital converter (LDC) for the long-time continuous monitoring of the photoplethysmography (PPG) signal. The design system incorporates a transimpedance amplifier (TIA), a delta-sigma modulator (DSM), and a decimation filter. The analog front-end circuit is implemented in the integrated chip with the chip area of 2.76 mm2 and fabricated via TSMC T18 process. The standard supply voltage used for the experiment is 1.8 V. The measurement result shows that the TIA – 3 db gain is 100 dB gain and – 3 dB cutoff frequency is 110 kHz. The design delta-sigma modulator can achieve the signal to noise plus distortion ratio (SNDR) of 50 dB at – 10 dB of the input signal. The measured signal to spurious-free dynamic range (SFDR) of the DSM is 50 dB. The measured effective number of the bit is (ENOB) of 8.3 bits. The on-chip 4th order decimation filter is used herein to convert the one-bit output of the DSM to the multibit output with a down sampling rate of 64 Hz. The measured cutoff frequency of the decimation filter is 10 Hz, and the operating sampling frequency is 1280 samples/seconds. Therefore, the overall designed bandwidth of the design system is 10 Hz bandwidth. The power consumption of the whole circuit is less than 100 µW. The achieved bandwidth of 10 Hz is the best among all the reported to date.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Ahmad S et al (2012) Electrocardiogram-assisted blood pressure estimation. IEEE Trans Biomed Eng 59(3):608–618. https://doi.org/10.1109/TBME.2011.2180019
Forouzanfar M, Ahmad S, Batkin I, Dajani HR, Groza VZ, Bolic M (2013) Coefficient-free blood pressure estimation based on pulse transit time–cuff pressure dependence. IEEE Trans Biomed Eng 60(7):1814–1824. https://doi.org/10.1109/TBME.2013.2243148
Hogenauer EB (1987) An economical class of digital filters for decimation and interpolation. IEEE Trans Acoust ASSP 29:155–162. https://doi.org/10.1109/TASSP.1981.1163535
Kao YH, Chao PC-P, Wey CL (2018) Towards maximizing the sensing accuracy of an cuffless, optical blood pressure sensor using a high-order front-end filter. Microsyst Technol. https://doi.org/10.1007/s00542-018-3877-3
Kao YH, Chao PC-P, Wey CL (2019) Design and validation of a new PPG module to acquire high-quality physiological signals for high-accuracy biomedical sensing. IEEE J Sel Top Quantum Electron. https://doi.org/10.1109/JSTQE.2018.2871604
Konijnenburg M, Stanzione S, Yan L et al (2016) A Multi (bio) sensor acquisition system with and two PPG readouts. IEEE J Solid-State Circ 51:2584–2595. https://doi.org/10.1109/JSSC.2016.2605660
Lee Y, Lee H, Jang J et al (2017) Sticker-Type hybrid photoplethysmogram monitoring system integrating CMOS IC with organic optical sensors. IEEE J Emerg Sel Top Circ Syst 7:50–59. https://doi.org/10.1109/JETCAS.2016.2630301
Lin B et al (2019) 14.85 μW analog front-end for photoplethysmography acquisition with 142-dBΩ gain and 64.2-pArms noise. Sensors (Basel, Switzerland) 19(3):512: https://doi.org/10.3390/s19030512
Lin Q, Xu J, Song S et al (2020) A 119dB dynamic range charge counting light-to-digital converter for wearable PPG/NIRS monitoring applications. IEEE Trans Biomed Circ Syst 14:800–810. https://doi.org/10.1109/TBCAS.2020.3001449
Marefat F, Erfani R, Kilgore KL, Mohseni P (2020a) A 280μW, 108dB DR PPG-readout IC with reconfigurable, 2nd-order, incremental ∑∆M Front-end for direct light-to-digital conversion. IEEE Trans Biomed Circ Syst. https://doi.org/10.1109/TBCAS.2020.3038046
Marefat F, Erfani R, Mohseni P (2020b) A 1-V 8.1-μ W PPG-recording front-end with > 92-dB DR using light-to-digital conversion with signal-aware DC subtraction and ambient light removal. IEEE Solid-State Circ Lett 3:17–20. https://doi.org/10.1109/LSSC.2019.2957261
Pandey RK, Pribadi EF, Chao PC-P (2019) A new adaptive readout system for a new OLED-OPD flexible patch. In: IEEE sensors conference. IEEE, Montreal. https://doi.org/10.1109/SENSORS43011.2019.8956825
Phang K, Johns DA (2001) A 1V 1mW CMOS front-end with on-chip dynamic gate biasing for a 75Mb/s optical receiver. In: International solid-state circuits conference. IEEE, San Francisco, pp 14–16. https://doi.org/10.1109/ISSCC.2001.912611
Pribadi EF, Pandey RK, Chao PC-P (2020) Optimizing a novel PPG sensor patch via optical simulations towards accurate heart rates. Microsyst Technol 26:3409–3420. https://doi.org/10.1007/s00542-020-04895-6
Rajesh PV, Valero-Sarmiento JM, Yan L et al (2016) A 172 µW compressive sampling photoplethysmographic readout with embedded direct heart-rate and variability extraction from compressively sampled data. In: Digest of technical papers—IEEE international solid-state circuits conference. https://doi.org/10.1109/ISSCC.2016.7418069
Rout S, Serdijn W (2018) High-pass ΣΔ converter design using a state-space approach and its application to cardiac signal acquisition. IEEE Trans Biomed Circ Syst 12:483–494. https://doi.org/10.1109/TBCAS.2018.2817926
Sharma A et al (2017) A sub-60-multimodal smart biosensing SoC with >80-dB SNR, 35-photoplethysmography signal chain. IEEE J Solid State Circuits 52(4):1021–1033. https://doi.org/10.1109/JSSC.2016.2642205
Tang SC, Huang PW, Hung CS et al (2017) Identification of atrial fibrillation by quantitative analyses of fingertip photoplethysmogram. Sci Rep 7:45644. https://doi.org/10.1038/srep45644
Vercaemer D, Raman J, Rombouts P (2017) Passive loop filter assistance for CTSDMs. IEEE Trans Circ Syst II Express Briefs 64:1157–1161. https://doi.org/10.1109/TCSII.2016.2633002
Wang G, Atef M, Lian Y (2018) Towards a continuous non-invasive cuffless blood pressure monitoring system using PPG: systems and circuits review. IEEE Circ Syst Mag 18:6–26. https://doi.org/10.1109/MCAS.2018.2849261
Zheng Y, Yan BP, Zhang Y, Poon CCY (2014) An Armband wearable device for overnight and cuff-less blood pressure measurement. IEEE Trans Biomed Eng 61(7):2179–2186. https://doi.org/10.1109/TBME.2014.2318779
Acknowledgements
This study is supported by Ministry of Science and Technology, Taiwan grant No. MOST 108-2823-8-009-002-, 108-2623-E-009-004-D, and 109-2622-8-009-018-TE1. This work was financially supported by the "Center for Intelligent Drug Systems and Smart Bio-devices (IDS2B)" from The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan. It was also supported in part by Hsinchu Science Park Bureau, MOST Grant No. 108A31B.
Author information
Authors and Affiliations
Corresponding author
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Eka Fitrah Pribadi and Rajeev Kumar Pandey contributed equally to this work as first author.
Rights and permissions
About this article
Cite this article
Pribadi, E.F., Pandey, R.K. & Chao, P.CP. Design and implementation of a new light to digital converter for the PPG sensor. Microsyst Technol 27, 2461–2472 (2021). https://doi.org/10.1007/s00542-020-05154-4
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00542-020-05154-4