Circuits for wearable vital sign monitors have very stringent requirements on power dissipation due to limited energy storage capacity and the need for a long lifetime.  Extending the time between battery recharge or replacement requires low-power electronics.  We report a micro-watt mixed-signal front-end (MSFE) for ECG monitoring ^[1] that uses aggressive voltage scaling to maximize power-efficiency and ensure compatibility with low-voltage DSPs ^[2] .  The MSFE shown in Figure 1 rejects 50/60Hz power-line interference (PLI) at the input of the system by using a mixed-signal feedback loop, enabling low-voltage operation by reducing dynamic range requirements.  Analog circuits are optimized for ultra-low-voltage, and a SAR ADC with a dual-DAC architecture eliminates the need for a power-hungry ADC buffer. Oversampling and ΔΣ-modulation leveraging integrated digital processing are used to achieve ultra-low-power operation without sacrificing noise performance and dynamic range.  Figure 2 shows ECG measurements on a male subject with the MSFE using gel electrodes and unshielded wiring.  The PLI is clearly canceled when the PLI filter is enabled. The MSFE was prototyped in a 0.18µm CMOS process and consumes 2.9µW from 0.6V.

1. M. Yip, J. L. Bohorquez, and A. P. Chandrakasan, “A 0.6V 2.9µW mixed-signal front-end for ECG monitoring,” IEEE Symposium on VLSI Circuits, pp. 66-67, Honolulu, HI, Jun. 2012.
2. J. Kwong and A. P. Chandrakasan, “An energy-efficient biomedical signal processing platform,” IEEE J. Solid-State Circuits, vol. 46, no. 7, pp. 1742-1753, Jul. 2011.