High Input Impedance Front-End Amplifier for Noncontact Bio-Potential Recording

In this paper, a high input impedance front-end amplifier is proposed for non-contact bio-potential recording systems. The proposed structure uses a positive feedback network to deliver a neutralization current back to the input node of the circuit to neutralize the current drawn by the parasitic capacitances at the input node of the employed Opamp. Since the neutralization current delivered by the positive feedback is equal to the current of the negative feedback loop drawn by the parasitic capacitances of the negative input node, it maximizes the input impedance and maintains the stability of the circuit. Moreover, the proposed technique demands neither an auxiliary Op-amp nor a manually-controlled potentiometer/capacitor array, leading to a reduction in noise, silicon area, and power dissipation of the front-end amplifier. Post-layout simulation results of the proposed front-end amplifier in a 0.18-μm CMOS technology show that, at the input frequency of 1kHz, the proposed front-end amplifier achieves an input impedance and the input noise of 55 GΩ and 26 nV Hz, respectively, at the cost of 14.2μW power consumption.