This paper presents the implementation of a wearable wireless sensor network aimed at monitoring harmful gases in industrial environments. The proposed solution is based on a customized wearable sensor node using a low-power low-rate wireless personal area network (LR-WPAN) communications protocol, which as a first approach measures CO₂ concentration, and employs different low power strategies for appropriate energy handling which is essential to achieving long battery life. These wearables nodes are connected to a deployed static network and a web-based application allows data storage, remote control and monitoring of the complete network. Therefore, a complete and versatile remote web application with a locally implemented decision-making system is accomplished, which allows early detection of hazardous situations for exposed workers.

This brief presents an ultralow-power class-AB operational amplifier (OpAmp) designed in a low-cost 0.18- μm CMOS technology. The proposed circuit uses transistors biased in the subthreshold region for low-voltage low-power operation. For a 0.8-V single supply, this OpAmp has 51-dB open-loop gain, 57-kHz unity-gain frequency, 60° phase margin, and 65-dB common-mode rejection ratio for 8-pF loads with a power consumption of only 1.2 μW. Experimental results illustrate performances such as a 0.14-V/μs slew rate and a 750-mV linear output swing, demonstrating its correct functionality.

Dual-phase lock-in amplifiers (LIAs) are designed to extract information (amplitude and phase) from signals buried in high noise levels. In spite of their popularity, their use has been traditionally limited to input sinusoidal waves with symmetric power supplies. This paper presents an algorithm that enables single-supply analog LIAs to properly process input square waves. Formed by linear equations, its computational implementation is much simpler than that of the traditional sinusoidal algorithm. Moreover, applied to battery-operated microcontrolled systems where square signals can be generated by the embedded microcontroller, it presents intrinsic advantages such as simplicity, versatility, and reduction in power and size. Experimental results validate the proposed algorithm, confirming its enormous possibilities in sensing applications.

Presented is a 3 V single supply analogue lock-in amplifier designed for processing output sensor signals in highly noisy environments. The proposed amplifier uses square input signals instead of the usual sinusoidal signals, consequently allowing a straight interface with microcontroller-based sensing systems working with both resistive and capacitive transducers. Experimental results for noisy signals with DC voltage variation confirm the capability of the proposed solution to effectively recover information from signal-to-noise ratios down to −24 dB with errors below 6% and with an average power consumption of only 5 mW in full operation.

This work presents a low-rate wireless personal area network-based sensor network for early detection and monitoring of forest fires. The system has been designed to perform different parameter measurements at different tree heights, depending on the forest relief. Thereby, it is possible to know how fire affects the soil mantle, stems and treetops, as well as to detect underground fires. Measures of power consumption confirm the feasibility of the implementation of this sensor network. Using a duty cycle of 0.33% and with the selected low-voltage-low-power compliant sensors, the network operating life is greater than one year.

This paper presents a new first-order temperature compensated CMOS current reference. To achieve a compact architecture able to operate under low voltage with low power consumption, it is based on a self-biasing beta multiplier current generator. Compensation against temperature is achieved by using instead of an ordinary resistor two triode transistors in parallel, acting as a negative and a positive temperature coefficient resistor, that generate a proportional to absolute temperature and a complementary to absolute temperature current which can be directly added to attain a temperature compensated current. Programmability is included to adjust the temperature coefficient and the reference current magnitude over process variations. Results for a 0.18 μm CMOS implementation show that the proposed 500 nA reference operate with supplies down to 1.2 V accomplishing over a (-40 to +120°C) range temperature drifts below 120 ppm/°C.