This article presents a low-power eddy-current sensor interface for touch applications. It is based on a bang-bang digital phase-locked loop (DPLL) that converts the displacement of a metal target into digital information. The PLL consists of a digitally controlled oscillator (DCO) built around a sensing coil and a capacitive DAC, a comparator-based bang-bang phase/frequency detector (PFD), and a digital loop filter (DLF). The PLL locks the DCO to a reference frequency, making its digital input a direct representation of the sensing coil inductance. To compensate for the coil inductance tolerances, the DCO’s center frequency can be trimmed by a second capacitive DAC. This approach obviates the need for a reference coil. When combined with a 5-mm-diameter sensing coil located $500~\mu \text{m}$ from a metal target, the interface achieves a displacement resolution of 6.7 nm (rms) in a 3-kHz bandwidth. It consumes $200~\mu \text{W}$ from a 1.8-V power supply, which represents the best-reported tradeoff between power consumption, bandwidth, and resolution.

中文翻译：

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一个200-μW接口，用于高分辨率涡流位移传感器

本文介绍了一种用于触摸应用的低功耗涡流传感器接口。它基于爆炸式数字锁相环（DPLL），可将金属目标的位移转换为数字信息。PLL由围绕感应线圈和电容DAC构成的数控振荡器（DCO），基于比较器的爆炸相位/频率检测器（PFD）和数字环路滤波器（DLF）组成。PLL将DCO锁定到参考频率，使其数字输入直接表示感测线圈电感。为了补偿线圈电感公差，可以通过第二个电容式DAC调整DCO的中心频率。这种方法消除了对参考线圈的需要。与定位的5毫米直径感应线圈结合使用时 $ 500〜\ mu \ text {m} $ 在金属靶材上，该界面在3 kHz带宽内可实现6.7 nm（rms）的位移分辨率。它消耗 $ 200〜\ mu \ text {W} $ 采用1.8V电源供电，这代表了功耗，带宽和分辨率之间最佳的折衷方案。