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In this paper, we propose a novel interface concept for eddy current displacement sensors. A measurement method and a new front-end circuit are also proposed. The front-end circuit demonstrates excellent thermal stability, high resolution, and low-power consumption. The proposed idea is analytically investigated. The demodulation principle, as well as the interface implementation, is also addressed. This interface is being introduced for measuring submicrometer displacements in medium- to high-resolution applications. The interface system consumes less than 12 mW and has an extremely low thermal drift. The interface circuit will be implemented as a system-in-a-package (SIP). The full-scale range of displacement is 1 mm with 50-kHz signal bandwidth and 11-bit resolution (less than 500 nm). The signal conditioning circuit utilizes a standard 0.35-μm complementary metal-oxide semiconductor (CMOS) technology. Simulation resuIts, which were achieved on the basis of experimental results of testing a prototype coil, also confirm the high performance of the interface system, as expected from analytical results. Compared with previous reports, this low-power interface system demonstrates a much lower temperature drift. [ABSTRACT FROM AUTHOR]

In eddy-current displacement sensing, existing techniques mostly involve a high-frequency sinusoidal carrier wave and deal with the demodulation of this signal. In this paper, we give a new design idea. We use switching circuits, in which the sensing coil is included as an inductor and driven by a switching voltage, and some baseband sensor output is readily available. Thus, no explicit demodulation is needed, and the electronics are simplified. We give three designs of such switching circuits. The first is based on coil inductance, the second is also based on coil inductance but is different from the first in many ways, and the third is based on eddy-current power loss. These circuits are tested on hardware electronics. The results seem to indicate that the presented techniques would permit performances comparable to those achieved by existing techniques. [ABSTRACT FROM AUTHOR]