Low-voltage low-power integrated analog lock-in amplifier for gas sensor applications

We propose a low-voltage (±1 V) low-power (3 mW) lock-in amplifier, fabricated in a standard CMOS technology (AMS 0.35 μm) with analog features and utilized for low-frequency gas sensor applications. The proposed lock-in architecture, which works at a fixed input signal frequency (77 Hz) with a very low input noise (only 34 nV/(sqrt(Hz)) @ 77 Hz), can be utilized to detect very small quantities of reagent gas, especially if combined with other techniques, as the sensor thermal modulation. The integrated solution has been fabricated on a single chip, requiring a reduced silicon area (about 5 mm2). Experimental measurements have confirmed the capability of the proposed lock-in system to reveal very small signals, in particular, testing the whole system for gas detection, a resolution improvement by a factor valued about 50 allows to detect gas concentrations lower than 1 ppm.