A 3.9 mW 25-Electrode Reconfigured Sensor for Wearable Cardiac Monitoring System

TLDR

The authors designed a low‑power, highly sensitive Thoracic Impedance Variance and ECG monitoring system‑on‑chip that is integrated into a poultice‑like plaster sensor for wearable cardiac monitoring. The SoC employs a high‑Q balanced sinusoidal current source, low‑noise reconfigurable readout, cm‑scale 13.56 MHz inductive coupling for remote control, 5 % duty‑cycled body‑channel communication, and occupies 5 mm × 5 mm in 0.18 µm CMOS, all mounted on a 15 cm × 15 cm fabric board with a flexible battery. It achieves 0.1 Ω TIV detection with 3.17 V/Ω sensitivity and >40 dB SNR, dissipates 3.9 mW peak power in receiver mode and 2.4 mW in detection mode, and enables TIV/ECG sensing at 16 heart sites using 25 adhesive electrodes.

Abstract

A low power highly sensitive Thoracic Impedance Variance (TIV) and Electrocardiogram (ECG) monitoring SoC is designed and implemented into a poultice-like plaster sensor for wearable cardiac monitoring. 0.1 Ω TIV detection is possible with a sensitivity of 3.17 V/Ω and SNR > 40 dB. This is achieved with the help of a high quality (Q-factor > 30) balanced sinusoidal current source and low noise reconfigurable readout electronics. A cm-range 13.56 MHz fabric inductor coupling is adopted to start/stop the SoC remotely. Moreover, a 5% duty-cycled Body Channel Communication (BCC) is exploited for 0.2 nJ/b 1 Mbps energy efficient external data communication. The proposed SoC occupies 5 mm × 5 mm including pads in a standard 0.18 μm 1P6M CMOS technology. It dissipates a peak power of 3.9 mW when operating in body channel receiver mode, and consumes 2.4 mW when operating in TIV and ECG detection mode. The SoC is integrated on a 15 cm × 15 cm fabric circuit board together with a flexible battery to form a compact wearable sensor. With 25 adhesive screen-printed fabric electrodes, detection of TIV and ECG at 16 different sites of the heart is possible, allowing optimal detection sites to be configured to accommodate different user dependencies.