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A Self-Sustained CMOS Microwave Chemical Sensor Using a Frequency Synthesizer

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8 Author(s)
Ahmed A. Helmy ; Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA ; Hyung-Joon Jeon ; Yung-Chung Lo ; Andreas J. Larsson
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In this paper, a CMOS on-chip sensor is presented to detect dielectric constant of organic chemicals. The dielectric constant of these chemicals is measured using the oscillation frequency shift of an LC voltage-controlled oscillator (VCO) upon the change of the tank capacitance when exposed to the liquid. To make the system self-sustained, the VCO is embedded inside a frequency synthesizer to convert the frequency shift into voltage that can be digitized using an on-chip analog-to-digital converter. The dielectric constant is then estimated using a detection procedure including the calibration of the sensor. The dielectric constants of different organic liquids have been detected in the frequency range of 7-9 GHz with an accuracy of 3.7% compared with theoretical values for sample volumes of 10-20 μL. The sensor is also applicable for binary mixture detection and estimation of the fractional volume of the constituting materials with an accuracy of 1%-2%.

Published in:

IEEE Journal of Solid-State Circuits  (Volume:47 ,  Issue: 10 )