A 3.51µW 0.31µVrms Biofuel Cell Enabled Integrated Analog CMOS Front-End in 130 nm CMOS

Abstract

Biofuel cell as an efficient energy converter is a promising biocompatible technology which harvests the blood glucose into usable electrical energy and replaces the toxic lithium-based battery solutions. However, the promise of this perennial non-toxic power system 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 a standalone enzymatic biofuel cell 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 protein crosslinks by glutaraldehyde. An integrated piezo-resistive analog front-end is demonstrated including cascaded dual-supply amplifier with a successive approximation register (SAR-ADC) and single-opamp relaxation oscillator occupying 1.12mm2• A switched-resistor biasing scheme using on-chip duty-cycled clock is proposed achieving measured input-referred noise of only $0.31\mu \mathrm{V}_{\mathrm{RMS}}$. The proposed hybrid power scheme uses $1.61\mu \mathrm{W}$ from the battery with 1.9 µW provided by the biofuel cell. Measured results show on-chip gain and noise variations across temperature of only 1.1 dB and $19.2\ nV/\sqrt{Hz}$ respectively with noise (power) efficient factor of of 1.46 (1.63).