No abstract

No abstract

This paper presents a comprehensive study of the design aspects of eddy-current displacement sensor (ECS) systems. In accordance with the sensor analysis presented in this paper, design strategies to compensate for important sensor imperfections are recommended. To this end, the challenges that are associated with ECS interfaces are identified, with focus on advanced industrial applications. This paper also provides a technical overview of the design advances of ECS interfaces proposed in the last decade and evaluates their pros and cons. Recently reported interface solutions for demanding industrial applications with respect to high resolution, stability, bandwidth, and low power consumption, at a sufficiently high excitation frequency, are addressed in more detail.

This paper describes an energy-efficient bridge readout IC (ROIC), which consists of a capacitively coupled instrumentation amplifier (CCIA) that drives a continuous-time delta-sigma modulator (CTM). By exploiting the CCIA's ability to block dc common-mode voltages, the bridge's bias voltage may exceed the ROIC's supply voltage, allowing these voltages to be independently optimized. Since bridge output is typically much smaller than bridge offset, a digital to analog converter (DAC) is used to compensate this offset before amplification and thus increase the CCIA's useful dynamic range. Bridge loading is reduced by using a dual-path positive feedback scheme to boost the CCIA's input impedance. Furthermore, the CCIA's output is gated to avoid digitizing its output spikes, which would otherwise limit the ROIC's linearity and stability. The ROIC achieves an input-referred noise density of 3.7 nV/ √ Hz, a noise efficiency factor (NEF) of 5, and a power efficiency factor (PEF) of 44, which both represent the state of the art. A pressure sensing system, built with the ROIC and a differential pressure sensor (AC4010), achieves 10.1-mPa (1σ ) resolution in a 0.5-ms conversion time. The ROIC dissipates about 30% of the system's power dissipation and contributes about 6% of its noise power. To reduce the sensor's offset drift, a temperature compensation scheme based on an external reference resistor is used. After a two-point calibration, this scheme reduces bridge offset drift by 80× over a 50°C range.

No abstract