A 470 nA performance-enhanced instrumental amplifier for bio-signal acquisition

This paper proposes a novel approach for enhancing performance of instrumental amplifier(IA) for bio-signal recording application. Differential difference amplifier based structure performs high input impedance, and the subthreshold operation with capacitive-coupled chopping topology achieves a great noise efficiency. A DC servo loop is implemented without using pseudo-resistors to perform high-pass transfer function and suppress electrode offset. The circuit is designed in standard 0.18-μm CMOS technology and simulated over process corners at extreme temperatures. The results show the key specifications of IA are insensitive to process variations even under extreme temperatures. For typical case, the circuit achieves the input impedance up to 470 MΩs. The input referred noise is 4.7 μV(0.5 Hz to 2.5 kHz) while consuming a current of 470 nA from 1.2 V supply. Also, the circuit handles an electrode-offset of ±120 mV.

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