CardioLeads: An Eleven-Leads ECG Monitoring System with an Ultralow-Power CMOS SoC

This paper presents the CardioLeads, a compact wireless eleven-leads ECG monitoring device based on a 0.13-μm CMOS custom system-on-chip (SoC) designed for ultralow-power applications. The CardioLeads is designed to record the heart’s electrical activity from 11 different angles while being wearable under clothes. This approach contrasts with conventional medical ECG recording devices that are bulky and wired with external equipment. The proposed system achieves reduced bulk and improved wearability through a highly integrated SoC architecture and optimized rigid-flex PCB implementation, enabling compact multi-lead acquisition without conventional bulky front-end modules or cable assemblies. The CardioLeads SoC features eight fully differential recording channels, capable of extracting 11 ECG leads, a fully differential 10-bit capacitive successive approximation register (SAR) analog-to-digital converter (ADC), a digital controller with a custom master SPI interface, low-dropout regulators (LDOs), and level shifters to facilitate integration. The ECG recording channels are implemented using a custom fully differential, current-mirror-based bioamplifier that provides tunable gain and inherent band-pass filtering, while eliminating residual DC components and avoiding the use of pseudoresistors. The bioamplifier achieves an input-referred noise of 2.15 μVrmsover a 0.3-500 Hz bandwidth, a total harmonic distortion (THD) of 0.234%, and consumes 4.24 μA. The ADC achieves an effective number of bits (ENOB) of 9.18 while consuming 11 μA. Overall, the SoC draws as low as 347 μW from a 1.2-V supply. CardioLeads consumes as low as 8 mW (4.5 mA at 1.8-V), and has an autonomy of up to 60 hours with a 300 mAh battery.We report successful 11-lead ECG recordings, comparison with a commercial ECG monitor, as well as PQRST wave identification with participants.