This paper presents a new micropower analog lock-in amplifier (LIA) suitable for battery-operated applications thanks to its reduced size and power consumption as well as its operation with single-supply voltage. The proposed LIA was designed in a 0.18 µm CMOS process with a single supply voltage of 1.8 V. Experimental results show a variable DC gain ranging from 24.7 to 42 dB, power consumption of 417 µW and integration area of 0.013 mm². The LIA performance was demonstrated by measuring carbon monoxide concentrations as low as 1 ppm in dry N₂. The experimental results show that the response to CO of the sensing system can be considerably improved by means of the proposed LIA.

The signal from a resistive sensor must be converted into a digital signal to be compatible with a computer through an interface circuit. Resistance-to-Period converter, used as interface, is preferred if the resistance variations are very large. This paper presents the structure of an interface circuit for resistive sensors that is highly robust to component and power supply variations. Robustness is achieved by using the ratiometric approach, thus complex circuits or highly accurate voltage references are not necessary. To validate the proposed approach, a prototype was implemented using discrete components. Measurements were carried out considering a variation of ±35% in the single supply voltage and a range from 1 k $\mathsf{\Omega }$ to 1 M $\mathsf{\Omega }$ .

This paper presents a new low-power, low-voltage Resistance-to-Period Converter (RPC) for signal conditioning of resistive sensors whose equivalent resistance varies in more than one decade. Designed in a low cost 0.18 μm CMOS process, the proposed RPC attains a good compromise between linearity and power consumption, which makes it suitable for portable applications. Simulation results show that the linearity error is less than 1.6% for an input resistance range from 10kΩ to 100kΩ with power consumption lower than 46 μW at 1.2 V supply.

This paper presents a novel structure of Resistance- to-Period (R-T) Converter highly robust to supply and temperature variations. Robustness is achieved by using the ratiometric approach so that complex circuits or high accuracy voltage references are not necessary. To prove the proposed architecture of R-T converter, a prototype was implemented in a 0.18 $\mathsf{\mu }$ m CMOS process with a single supply voltage of 1.8 V and without any stable reference voltage. Experimental results show a maximum ±1.5% output signal variation for ±10% supply voltage variation and in a 3–95 ${}^{°}$ C temperature range.