28.4 A 143dB-Dynamic-Range 119dB-CMRR Capacitance-to-Digital Converter for High-Resolution Floating-Target Displacement Sensing

Displacement sensors are widely used in high-precision nanomechatronic systems [1]–[4]. Compared to eddy-current displacement sensors [1], capacitive displacement sensors are potentially more energy efficient [2]–[4]. However, they are more susceptible to electric-field interferences on an electrically floating target, especially at high frequencies. This paper presents a capacitive displacement sensor, in which sensing capacitance is converted to phase shift via a lowpass RC front-end and then digitized by a high-resolution Phase-Domain-Delta-Sigma modulator $(\text{PD}\Delta\Sigma\mathrm{M})$. With inherent high/low-pass noise filtering provided by the front-end/readout circuits, both low-frequency and high-frequency interferences are rejected, which can be reflected from the sensor's CMRR of 119dB near DC and 97dB around 100MHz. Also, the prototype sensor achieves a >143dB (35.2aF-to-500pF) dynamic range (DR) without sub-ranging and less than $24.7\text{ppm}/^{\circ} \mathrm{C}$ temperature drift.