Modeling and Analysis of the Noise Performance of the Capacitive Sensing Circuit with a Differential Transformer

Yafei Xie; Ji Fan; Chun Zhao; Shitao Yan; Chenyuan Hu; Liangcheng Tu

doi:10.3390/mi10050325

Modeling and Analysis of the Noise Performance of the Capacitive Sensing Circuit with a Differential Transformer

Micromachines (Basel). 2019 May 15;10(5):325. doi: 10.3390/mi10050325.

Authors

Yafei Xie¹, Ji Fan^{2

3}, Chun Zhao⁴, Shitao Yan⁵, Chenyuan Hu⁶, Liangcheng Tu^{7

8

9}

Affiliations

¹ MOE Key Laboratory of Fundamental Physical Quantities Measurement & Hubei Key Laboratory of Gravitation and Quantum Physics, PGMF and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China. xieyaphe@hust.edu.cn.
² MOE Key Laboratory of Fundamental Physical Quantities Measurement & Hubei Key Laboratory of Gravitation and Quantum Physics, PGMF and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China. fanji@hust.edu.cn.
³ Institute of Geophysics, Huazhong University of Science and Technology, Wuhan 430074, China. fanji@hust.edu.cn.
⁴ MOE Key Laboratory of Fundamental Physical Quantities Measurement & Hubei Key Laboratory of Gravitation and Quantum Physics, PGMF and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China. chun_zhao@hust.edu.cn.
⁵ MOE Key Laboratory of Fundamental Physical Quantities Measurement & Hubei Key Laboratory of Gravitation and Quantum Physics, PGMF and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China. yanshitao@hust.edu.cn.
⁶ MOE Key Laboratory of Fundamental Physical Quantities Measurement & Hubei Key Laboratory of Gravitation and Quantum Physics, PGMF and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China. chenyuanhu@hust.edu.cn.
⁷ MOE Key Laboratory of Fundamental Physical Quantities Measurement & Hubei Key Laboratory of Gravitation and Quantum Physics, PGMF and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China. tlc@hust.edu.cn.
⁸ Institute of Geophysics, Huazhong University of Science and Technology, Wuhan 430074, China. tlc@hust.edu.cn.
⁹ TianQin Research Center for Gravitational Physics and School of Physics and Astronomy, Sun Yat-sen University (Zhuhai Campus), Zhuhai 519082, China. tlc@hust.edu.cn.

Abstract

Capacitive sensing is a key technique to measure the test mass movement with a high resolution for space-borne gravitational wave detectors, such as Laser Interferometer Space Antenna (LISA) and TianQin. The capacitance resolution requirement of TianQin is higher than that of LISA, as the arm length of TianQin is about 15 times shorter. In this paper, the transfer function and capacitance measurement noise of the circuit are modeled and analyzed. Figure-of-merits, including the product of the inductance L and the quality factor Q of the transformer, are proposed to optimize the transformer and the capacitance measurement resolution of the circuit. The LQ product improvement and the resonant frequency augmentation are the key factors to enhance the capacitance measurement resolution. We fabricated a transformer with a high LQ product over a wide frequency band. The evaluation showed that the transformer can generate a capacitance resolution of 0.11 aF/Hz^1/2 at a resonant frequency of 200 kHz, and the amplitude of the injection wave would be 0.6 V. This result supports the potential application of the proposed transformer in space-borne gravitational wave detection and demonstrates that it could relieve the stringent requirements for other parameters in the TianQin mission.

Keywords: LQ product; capacitive sensing; differential transformer; low noise circuit; resonant frequency.

Abstract

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