Recent years have witnessed an improvement in the energy efficiency of capacitive sensor interfaces by more than three orders of magnitude. This article reviews the architectural and circuit innovations that have contributed to this progress. The fundamental limit on the energy consumption of capacitive sensor interfaces is discussed, as well as the widely used figure-of-merit (FoM). Interfaces based on period modulation feature simple circuitry, but their power efficiency at higher resolution deteriorates. Those employing Δ Σ modulation achieve high resolution with improved efficiency but require operational transconductance amplifiers that do not easily scale with process and supply voltage. Interfaces using successive approximation techniques feature mostly digital circuitry achieving good power efficiency at medium resolution. To achieve higher resolution, they can also be employed as the front-end in a hybrid architecture, where a back-end based on Δ Σ modulation or a voltage-controlled oscillator (VCO) performs a fine measurement on the front-end's residue, resulting in high resolution and excellent energy efficiency simultaneously.@en

This article presents a fully dynamic scalable switched-capacitor delta-sigma modulator that achieves a 94.1-dB dynamic range (DR). Power-and- bandwidth scalability by only changing the clock frequency is achieved using a capacitively biased and swing-enhanced floating inverter operational transconductance amplifier (OTA). Fabricated in a 180-nm CMOS process, the prototype achieves an signal-to-noise-and-distortion ratio (SNDR) of >87 dB across 4× scaling from 100 to 400 kHz of the sampling frequency f_ S. At 200-kHz f_ S , it achieves an SNDR/DR of 89.3/94.1 dB while consuming 4 μ W , leading to a DR-based Schreier figure of merit (FoM) of 177.1 dB. @en

IoT sensing applications operating from batteries or harvested energy require microwatt data converters. To accurately measure small signals, they often need to achieve a high DR (>90dB) and better linearity than the transducers themselves (>14b) with a BW in the kHz range. IoT systems also often consist of multiple sensing modalities with different BW requirements and are often heavily duty-cycled to reduce power consumption. This paper presents a fully dynamic discrete-time delta-sigma modulator (DTDSM) that supports 4x bandwidth/power scaling without any programming overhead except for changing fs, using a capacitively biased swing-enhanced floating inverter amplifier (SEFIA). The prototype, fabricated in 180nm CMOS, consumes only 4μW at 800Hz BW and achieves >87dB SNDR over 2 octaves of fs, between 100 kHz and 400 kHz, and a DR of 94.1 dB while operating with an OSR of 125.@en

The quote by Lord Kelvin, “if you can’t measure it, you can’t improve it,” best captures the invaluable role of sensors in any system. It also implies that to improve the performance of a system one needs to employ advanced sensor solutions. The performance requirements vary from one application to another, but are always associated with accuracy, repeatability, reproducibility, range, power consumption, ease of installation, and maintenance. In the modern era of data science, machine learning, and artificial intelligence, there is an ever-increasing need for low-cost, high-performing sensors in high volumes@en