External temperature sensor assisted a new low power photoplethysmography readout system for accurate measurement of the bio-signs

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 (S p O 2) 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.

An Adaptive Analog Front End for a Flexible PPG Sensor Patch with Self-Determined Motion Related DC Drift Removal

“…The process flow of the digital control and quality assessment unit is shown in Fig. 3, which comprised a moving average filtering, peak-through detection, periodicity check, amplitude check, power spectrum (PS) check, OLED array control and PGA gain control [18]. To implement this, a 4:1 analog multiplexer is designed in the AFE and the 2-bit select signal is used to turn ON the OLED one-by-one for 3 seconds.…”

“…The algorithm for the heart rate estimation is shown in 3 (b). The raw PPG signal will be filtered by the convolution filter [18], then the peak-peak interval/pulse repetition time (PRT) is measured to estimate the HR in the time domain. Also, the frequency (FHR) of the first harmonics of the single sided spectrum (Fig 3(c…”