A Perspective on Direct Binary Capacitance Detectors for Decision-Driven Biochemical and Lab-on-Chip Applications: A CMOS Cross-Coupled-Based Capacitance Detector.

Capacitive sensors implemented in complementary metal-oxide-semiconductor (CMOS) technology are widely used in lab-on-chip (LoC), biomedical, and microfluidic systems. While most capacitive sensor interfaces are designed for high-resolution capacitance quantification, many practical applications require only binary decisions, event detection, or state discrimination. In such scenarios, conventional readout architectures introduce unnecessary circuit complexity, power consumption, latency, and data-processing overhead. This paper presents a CMOS cross-coupled-based capacitance detector (CBCD) that directly converts the imbalance between a sensing capacitance and a reference capacitance into a digital output. By exploiting regenerative positive feedback in a dynamic latch architecture, the proposed detector integrates sensing, comparison, and digitization within a single stage, eliminating the need for analog amplification, analog-to-digital conversion, frequency-based readout, and external thresholding circuitry. Circuit-level simulations show the ability to detect extremely small capacitance differences, demonstrate robust operation across a wide range of input capacitances, and achieve negligible power consumption. Process-corner, noise, and Monte Carlo analyses further verify reliable operation in the presence of device mismatch and process variations. Owing to its compact structure, digital-native output, and energy-efficient operation, the proposed CBCD is well suited for decision-driven sensing applications, including droplet presence detection, bubble monitoring, threshold-based diagnostics, event detection, and time-of-evaporation (ToE) measurements. The proposed architecture provides a scalable and low-complexity front-end solution for next-generation CMOS-integrated sensing platforms.