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Sensors 2015, 15(10), 26009-26017; doi:10.3390/s151026009

Fully Integrated Low-Noise Readout Circuit with Automatic Offset Cancellation Loop for Capacitive Microsensors

1
Department of Electronics, Chungnam National University, Daejeon 305-764, Korea
2
ASRI/ISRC, Department of Electrical Engineering and Computer Science, Seoul National University, Seoul 151-744, Korea
*
Author to whom correspondence should be addressed.
Academic Editor: Vittorio M. N. Passaro
Received: 25 August 2015 / Revised: 7 October 2015 / Accepted: 9 October 2015 / Published: 14 October 2015
(This article belongs to the Section Physical Sensors)
View Full-Text   |   Download PDF [1859 KB, uploaded 14 October 2015]   |  

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. View Full-Text
Keywords: capacitive sensing circuit; automatic offset cancellation loop (AOCL); correlated double sampling (CDS); capacitive microsensor capacitive sensing circuit; automatic offset cancellation loop (AOCL); correlated double sampling (CDS); capacitive microsensor
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Song, H.; Park, Y.; Kim, H.; Cho, D.-I.D.; Ko, H. Fully Integrated Low-Noise Readout Circuit with Automatic Offset Cancellation Loop for Capacitive Microsensors. Sensors 2015, 15, 26009-26017.

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