Journal of Sensor Science and Technology (센서학회지)

The Korean Sensors Society (한국센서학회)
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A Microcontroller-Based Lock-In Amplifier for Capacitive Sensors

용량형 센서를 위한 마이크로컨트롤러에 기반을 둔 록인 증폭기

  • Kim, Cheong-Worl (Department of Information Technology & Electronics Education, Andong National University)
  • 김청월 (안동대학교 정보전자공학교육과)
  • Received : 2013.08.13
  • Accepted : 2013.11.28
  • Published : 2014.01.29
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Abstract

A lock-in amplifier was proposed for capacitive sensor applications. This amplifier was based on a general-purpose microcontroller and had only a charge amplifier as analog circuits. All the other functions of lock-in amplifier except for the charge amplifier were implemented with firmware and the internal resources of the microcontroller. A rectangular signal, generated by the microcontroller, was used in a sensor-driving signal instead of a conventional sinusoidal signal. This makes it possible that the phase comparison circuit in the lockin amplifier is made with analog-to-digital converter, a timer and an interrupt controller. Using the oversampling method and the rectangular driving signal, we can make it easy to implement the peak detection function with software and sample the peak-to-peak signal at charge amplifier output. A charge amplifier was proposed to cancel out the base capacitance existing in capacitive sensors structurally. The experimental results show that the lock-in amplifier operating in the supply voltage of 3.0 V cancels out the base capacitance and has good linearity.

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References

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