Ultra-High Input Impedance, Low Noise Integrated Amplifier for Noncontact Biopotential Sensing

Noncontact electrocardiogram/electroencephalogram/electromyogram electrodes, which operate primarily through capacitive coupling, have been extensively studied for unobtrusive physiological monitoring. Previous implementations using discrete off-the-shelf amplifiers have been encumbered by the need for manually tuned input capacitance neutralization networks and complex dc-biasing schemes. We have designed and fabricated a custom integrated noncontact sensor front-end amplifier that fully bootstraps internal and external parasitic impedances. DC stability without the need for external large valued resistances is ensured by an ac bootstrapped, low-leakage, on-chip biasing network. The amplifier achieves, without neutralization, input impedance of 60 fF $\Vert$ 50 T $\Omega$ , input referred noise of 0.05 fA/ $\sqrt {\rm Hz}$ and 200 nV/ $\sqrt {\rm Hz}$ at 1 Hz, and power consumption of 1.5 $\mu$ A per channel at 3.3 V supply voltage. Stable frequency response is demonstrated below 0.05 Hz with electrode coupling capacitances as low as 0.5 pF.