High-Resolution Battery-Less Miniaturized Power Grid Monitoring System Employing a Capacitive Sensing Current-Mode ΣΔ Modulator

This paper presents a battery-less power grid monitoring system that employs capacitive coupling to measure both the fundamental voltage component and its harmonic distortion components. The system integrates an electric field energy harvester—comprising a capacitive AC–DC rectifier and a buck–boost converter—that achieves over 80% peak efficiency at input power levels above 30 μW, and can be scaled if necessary. The harvested energy is stored in a 1F supercapacitor, enabling RF transmission with a power amplifier current of up to 100mA. Spectral analysis is performed using a low-power current-mode ΣΔ modulator achieving a 67 dB signal-to-noise-and-distortion ratio (SNDR), corresponding to 10.8 effective number of bits (ENOB), over a 200 Hz bandwidth. A passive second-order switched-capacitor (SC) filter is employed in the ΣΔ modulator loop, resulting in a total power consumption of only 12 μW. A distinguishing feature of the sensing architecture is its use of the displacement current through the coupling capacitor, which inherently amplifies the nth harmonic by n, enabling detection down to →70 dB. A prototype was fabricated in 180nm CMOS, occupying 0.2mm2 and 3.8mm2 for the energy harvester and the modulator, respectively.