Direct Interface Circuits for Resistive, Capacitive, and Inductive Sensors

This paper presents a comprehensive review of Direct Interface Circuits (DICs), which provide a compact, cost-effective, and energy-efficient alternative for interfacing with sensors that exhibit electrical variations such as resistance, capacitance, and inductance. A distinctive characteristic of DICs is their ability to connect sensors directly to digital processors, including microcontrollers (MCUs) or Field-Programmable Gate Arrays (FPGAs), through RC, RL, or capacitive charge transfer configurations, without the need for additional signal conditioning components. The review outlines the fundamental operating principles and key elements of DICs, including time-to-digital conversion, digital processing, and techniques for assessing measurement accuracy, resolution, response time, and the effects of uncertainty and interference. By synthesizing findings from recent literature, this study provides an in-depth understanding of current advancements in DICs and offers a critical analysis of their state-of-the-art implementations. Finally, strategic recommendations are proposed to guide future research directions and application areas.