title: A Digital Lock-In Amplifier for Use at Temperatures of up to 200 °C.
abstract: Weak voltage signals cannot be reliably measured using currently available logging tools when these tools are subject to high-temperature (up to 200 °C) environments for prolonged periods. In this paper, we present a digital lock-in amplifier (DLIA) capable of operating at temperatures of up to 200 °C. The DLIA contains a low-noise instrument amplifier and signal acquisition and the corresponding signal processing electronics. The high-temperature stability of the DLIA is achieved by designing system-in-package (SiP) and multi-chip module (MCM) components with low thermal resistances. An effective look-up-table (LUT) method was developed for the lock-in amplifier algorithm, to decrease the complexity of the calculations and generate less heat than the traditional way. The performance of the design was tested by determining the linearity, gain,Qvalue, and frequency characteristic of the DLIA between 25 and 200 °C. The maximal nonlinear error in the linearity of the DLIA working at 200 °C was about 1.736% when the equivalent input was a sine wave signal with an amplitude of between 94.8 and 1896.0 nV and a frequency of 800 kHz. The tests showed that the DLIA proposed could work effectively in high-temperature environments up to 200 °C.
authors.affiliation: School of Automation, Huazhong University of Science and Technology, Wuhan 430074, China. chengjj@hust.edu.cn.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Cheng
authors.affiliation: School of Automation, Huazhong University of Science and Technology, Wuhan 430074, China. xyjdyx643@hust.edu.cn.
authors.forename: Yingjun
authors.initials: Y
authors.lastname: Xu
authors.affiliation: School of Chemical Engineering and Environment, Beijing Institute of Technology, Beijing 100000, China. wulei@bit.edu.cn.
authors.forename: Lei
authors.initials: L
authors.lastname: Wu
authors.affiliation: Well-Tech R&D Institutes, China Oilfield Service Limited, Beijing 101149, China. wanggw4@cosl.com.cn.
authors.forename: Guangwei
authors.initials: G
authors.lastname: Wang
keywords: LUT method; MCM; SiP; digital lock-in amplifier; high temperature; thermal resistance