title: Fully integrated low-noise readout circuit with automatic offset cancellation loop for capacitive microsensors.
abstract: Capacitive sensing schemes are widely used for various microsensors; however, such microsensors suffer from severe parasitic capacitance problems. This paper presents a fully integrated low-noise readout circuit with automatic offset cancellation loop (AOCL) for capacitive microsensors. The output offsets of the capacitive sensing chain due to the parasitic capacitances and process variations are automatically removed using AOCL. The AOCL generates electrically equivalent offset capacitance and enables charge-domain fine calibration using a 10-bit R-2R digital-to-analog converter, charge-transfer switches, and a charge-storing capacitor. The AOCL cancels the unwanted offset by binary-search algorithm based on 10-bit successive approximation register (SAR) logic. The chip is implemented using 0.18 μm complementary metal-oxide-semiconductor (CMOS) process with an active area of 1.76 mm². The power consumption is 220 μW with 3.3 V supply. The input parasitic capacitances within the range of -250 fF to 250 fF can be cancelled out automatically, and the required calibration time is lower than 10 ms.
authors.affiliation: Department of Electronics, Chungnam National University, Daejeon 305-764, Korea. zealshr@cnu.ac.kr.
authors.forename: Haryong
authors.initials: H
authors.lastname: Song
authors.affiliation: Department of Electronics, Chungnam National University, Daejeon 305-764, Korea. pyjj90@cnu.ac.kr.
authors.forename: Yunjong
authors.initials: Y
authors.lastname: Park
authors.affiliation: Department of Electronics, Chungnam National University, Daejeon 305-764, Korea. hanafos24@cnu.ac.kr.
authors.forename: Hyungseup
authors.initials: H
authors.lastname: Kim
authors.affiliation: ASRI/ISRC, Department of Electrical Engineering and Computer Science, Seoul National University, Seoul 151-744, Korea. dicho@snu.ac.kr.
authors.forename: Dong-Il Dan
authors.initials: DI
authors.lastname: Cho
authors.affiliation: Department of Electronics, Chungnam National University, Daejeon 305-764, Korea. hhko@cnu.ac.kr.
authors.forename: Hyoungho
authors.initials: H
authors.lastname: Ko
keywords: automatic offset cancellation loop (AOCL); capacitive microsensor; capacitive sensing circuit; correlated double sampling (CDS)