A low-power readout circuit for nanowire based hydrogen sensor

This paper presents a fully integrated lock-in amplifier intended for nanowire gas sensing. The nanowire will change its conductivity according to the concentration of an absorbing gas. To ensure an accurate nanowire impedance measurement, a lock-in technique is implemented to attenuate the low frequency noise and offset by synchronous demodulation or phase-sensitive detection (PSD). The dual-channel lock-in amplifier also provides both resistive and capacitive information of the nanowire in separate channels. Measurement results of test resistors and capacitors show a 2% resolution in the resistance range 10-40k@W and a 3% resolution in the capacitance range 0.5-1.8nF. Moreover, a 28.7-32.1k@W impedance variation was measured through the lock-in amplifier for a single palladium nanowire that was exposed to a decreasing hydrogen concentration (10% H"2 in N"2 to air). The chip has been implemented with UMC 0.18@mm CMOS technology and occupies an area of 2mm^2. The power consumption of the readout circuit is 2mW from a 1.8V supply.

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