A 4-μW Analog Front End Achieving 2.4 NEF for Long-Term ECG Monitoring

An ultra-low-power low-noise analog front end (AFE) is presented in this work, aiming for long-term ECG with clear P-waves for clinical diagnose. The chopper amplifier with passive noise filter and PWM based offset cancellation results in an input-reference noise of 0.39 μVrms, which shows 3.7X noise improvements among the state-of-the-art designs. With the digital offset cancellation by the pulse-width modulation wave, the AFE achieves a low input-referred dc offset of 0.4 μV among 9 tested chips and a low drift under 30 μV. A dynamic scale ADC with low-power comparator strategy prevents the instability and signal-loss, achieving an SFDR of 71.6 dB. The proposed AFE achieves a noise-efficient-factor (NEF) of 2.4 with a power consumption of 4 μW. The fabricated chip is demonstrated in a miniature prototype for long-term ECG monitoring application, presenting a clear ECG waveform with visible P-wave. The simultaneously ECG recording with a medical grade 12-lead ECG Holter shows the effective acquisition of the prototype, proofing the better noise performance.