From Battery Enabled to Natural Harvesting: Enzymatic BioFuel Cell Assisted Integrated Analog Front-End in 130nm CMOS for Long-Term Monitoring

Biofuel cell as a natural energy source is a promising biocompatible technology which harvests the blood glucose into usable energy and replaces the toxic lithium-based battery solutions. However, the promise of this perennial non-toxic power is tempered by its unstable operation and low-voltage outputs leading to very limited operational lifetimes. This paper demonstrates a glucose-powered analog front-end with superior noise performance, which is enabled by standalone enzymatic biofuel cells operating for more than 30 min on active power without replenishment. Two biofuel cells are stacked to realize 0.5V output using commercially available glucose oxidase and the enzyme stability is improved via multipoint crosslinks by glutaraldehyde. To mitigate the effects of noisy and temperature-sensitive pseudo-resistors, a switched-resistor biasing scheme is applied to the input amplifier with the measured input-referred noise of 0.31 μV RMS only. The proposed hybrid power scheme uses 1.6 μW from the battery with 1.9 μW provided by the biofuel cells. The entire analog front-end including a cascaded dual-supply amplifier with switched-capacitor SAR ADC and single-opamp relaxation oscillator occupies 1.12 mm 2 . Measured of only 1.1 dB and 19.2 nV/√Hz, respectively, with noise (power) results show on-chip gain and noise variations across temperature efficient factor of 1.46 (1.63).