A Hybrid Voltage-Time Dual-Slope Capacitance-to-Digital Converter With Noise Shaping for Extracellular Vesicle Sensing Systems

This paper presents a low-noise sensing system for early cancer detections, specifically targeting the biological protein microRNA within extracellular vesicles (EVs). The proposed sensing system integrates a CMOS MEMS transducer with a front-end readout circuit and utilizes a hybrid ADC for data conversion. The front-end readout circuit is designed to be less sensitive to parasitic capacitance, effectively suppressing interface noise. Additionally, the hybrid voltage-to-time ADC does not require an extra voltage-to-time converter (VTC) between the coarse and fine converters, thereby maintaining conversion linearity. Experimental results demonstrate a capacitance resolution of 10.3 fF and a microRNA-195 concentration detection range from 10 fM to 10 pM. The proposed EV sensing system achieves first-order noise shaping and reduces the required measurement time, with a FOM of $1.39 \mathrm{~nJ} /$ conversion-step.