A Self-Sustained CMOS Microwave Chemical Sensor Using a Frequency Synthesizer Ahmed A. Helmy , Student Member , IEEE , Hyung-Joon Jeon, Y ung-Chung Lo, Andreas J. Larsson , Student Member , IEEE , Raghavendra Kulkarni, Jusung Kim

Abstract

In this paper, a CMOS on-chip sensor is p resented to detect dielectric constant of or ganic chemicals. The dielectric constant of these chemicals is measured using the oscillation fre- quency 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 fre- quency synthesizer to convert the freq uency shift into voltage that can be digitized using an on-chip analog-to-digital converter. The dielectric constant is then estima ted using a detection procedure including the calibration of the sen sor. 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 L. The sensor is also appli- cable for binary mixture detection and estimation of the fractional volume of the constituting materials with an accuracy of 1%–2%.