A Low-Power On-Chip ECG Monitoring System Based on MWCNT/PDMS Dry Electrodes

• Published in: IEEE sensors journal 2020-11, Vol.20 (21), p.12799-12806
• Main Authors: Tasneem, Nishat T., Pullano, Salvatore A., Critello, Costantino Davide, Fiorillo, Antonino S., Mahbub, Ifana
• Format: Article
• Language: English
• Subjects: CMOS; Cutoff frequency; ECG signal recording; Electrocardiography; Electrodes; Feedback; Flexible and wearable dry electrodes; Integrated circuits; Kapton substrate; Metal oxide semiconductors; Monitoring; Multi wall carbon nanotubes; MWCNT/PDMS; Noise levels; Operational amplifiers; Polydimethylsiloxane; Power management; Sensors; Signal to noise ratio; Substrates; Transconductance; Transistors; two-stage differential amplifier; Wearable technology
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2020.3001209

Wearable technologies have established novel strategies for continuous electrocardiogram (ECG) monitoring, exploiting recent developments in sensors and integrated circuit technology. Advances in dry electrodes fabrication improved the growth of wearable devices. Herein, we present an on-chip integrated ECG signal acquisition system along with dry electrodes for wearable and long-term monitoring. Custom electrodes are fabricated using multi-walled carbon nanotube (MWCNT) and Polydimethylsiloxane (PDMS) composite on a flexible substrate. A 1.5~\mu \text{W} fully-differential operational transconductance amplifier (OTA) with a capacitive-resistive feedback network is designed in 130 nm CMOS process achieving a mid-band gain of 43.09 dB and an input-referred noise of 2.81~\mu \text{V}_{\textit {rms}} in the range from 0.175 Hz to 1.636 kHz. Reconfigurability of the lower cut-off frequency is achieved by controlling the bias voltage of the triple-well nMOS transistors acting as the feedback pseudoresistor. Electrodes with different surface area and MWCNT concentrations were investigated in a real-time ECG measurement scenario. The recorded signals achieve a high signal-to-noise ratio which spans from 35.7 dB to 38.6 dB with the increasing MWCNT concentration. Experimental results demonstrate that the proposed system allows for high performance and low-power ECG signal recording for the long-term and wearable applications.