DC-Coupled Fully Differential Difference Amplifier-Based Analog Front-End Design for Wearable ECG Sensors

Cardiovascular diseases (CVDs) are a significant cause of human death and impose a considerable economic burden on society. Early detection and prevention of CVDs can be achieved through home monitoring systems, utilizing wearable sensors to continuously record Electrocardiogram (ECG) signals from the human heart over extended periods of time. However, the design of a wearable biomedical sensor presents challenges, including motion artifact due to body movements and the need for low power consumption. In this research article, we propose an Analog Front End (AFE) that is DC coupled and consists of an FDDA-based Instrumentation Amplifier (IA) and a Programmable Gain Amplifier (PGA) with an AC coupled input stage. Our proposed AFE possesses the required characteristics for effective CVD detection, including high input impedance, low noise, high Common Mode Rejection Ratio (CMRR), and ultralow power. To address the challenge of motion artifact, we increase the AFE input impedance, while keeping the circuit as simple as possible for low power consumption. The proposed AFE is implemented in $0.18 \mu \mathrm{m}$ CMOS process with a supply voltage of 1.8V provides an excellent gain of 76dB, CMRR of around 127dB with less output noise voltage and high input impedance. Our AFE, when incorporated into a complete biomedical sensor, is capable of accurately detecting ECG signals in the range of 1-2 millivolt peak to peak, enabling the determination of heart rate or beats per minute.