External temperature sensor assisted a new low power photoplethysmography readout system for accurate measurement of the
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TECHNICAL PAPER
External temperature sensor assisted a new low power photoplethysmography readout system for accurate measurement of the bio-signs Rajeev Kumar Pandey1 • Paul C.-P. Chao2 Received: 1 November 2020 / Accepted: 7 November 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This study presents an external temperature sensor assisted a new low power, time-interleave, wide dynamic range, and low DC drift photoplethysmography (PPG) signal acquisition system to obtain the accurate measurement of various bio signs in real-time. The designed chip incorporates a 2-bit control programmable transimpedance amplifier (TIA), a high order filter, a 3:8 programmable gain amplifier (PGA) and 2 9 2 organic light-emitting diode (OLED) driver. Temperature sensor is used herein to compensate the adverse effect of low-skin-temperature on the PPG signal quality. The analog front-end circuit is implemented in the integrated chip with chip area of 2008 lm 9 1377 lm and fabricated via TSMC T18 process. With the standard 1.8 V, the experimental result shows that the measured current sensing range is 20 nA–100 uA. The measured dynamic range of the designed readout circuit is 80 dB. The estimated signal to noise ratio is 60 dB@1 uA, and the measured input referred noise is 60.2 pA/Hz. The total power consumption of the designed chip is 31.32 lW (readout) ? 1.62 mW (OLED driver@100% duty cycle). The non-invasive PPG sensor is applied to the wrist artery of the 40 healthy subjects for sensing the pulsation of the blood vessel. The experimental results show that for every 1 °C decrease in mean ambient temperature tends to 0.06 beats/min, 0.125 mmHg and 0.063 mmHg increase in hear rate (HR), systolic (SBP) and diastolic (DBP), respectively. Similarly, for every 1 °C increase in mean ambient temperature tends to 0.13 beats/min, 0.601 mmHg and 0.121 mmHg increase in HR, SBP and DBP, respectively. The measured accuracy and standard error for the HR estimation are 96%, and - 0.022 ± 2.589 beats/minute, respectively. The oxygen stauration (SpO2) measurement results shows that the mean absolute percentage error is less than 5%. The resultant errors for the SBP and DBP measurement are - 0.318 ± 5.19 mmHg and - 0.5 ± 1.91 mmHg, respectively.
1 Introduction With the rise of coronavirus disease (COVID-19) pandemic, vital bio signs like blood oxygen saturation (SpO2), body temperature, heart rate (HR) and blood pressure (BP) becomes one of the major concerns. According to the
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00542-020-05106-y) contains supplementary material, which is available to authorized users. & Paul C.-P. Chao [email protected] 1
EECS International Graduate Program, National Chiao Tung University, Hsinchu 300, Taiwan
2
Department of Electrical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan
WHO report, about 17.9 million peoples die every year due to cardiovascular disease, that
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