학술논문
A Reconfigurable Multichannel Capacitive Sensor Array Interface
Document Type
Periodical
Author
Source
IEEE Transactions on Instrumentation and Measurement IEEE Trans. Instrum. Meas. Instrumentation and Measurement, IEEE Transactions on. 60(9):3214-3221 Sep, 2011
Subject
Language
ISSN
0018-9456
1557-9662
1557-9662
Abstract
The design of a reconfigurable capacitive sensor array interface comprised of a subsystem able to read an array of capacitive-type sensors and an embedded processor is described. Each sensor is connected to a ring oscillator, which translates capacitive changes into a variable-frequency pulse train. An in-depth analysis of the oscillator behavior including all parasitic elements has been performed, and the use of a Schmitt trigger at the inverter chain is proposed to assure oscillation for capacitance values ranging from 1 to 1500 pF. The oscillation frequency is estimated by using a 16-b counter and the appropriate user-defined counting interval ranging from a few microseconds to several seconds in order to achieve maximum accuracy within the entire capacitance range. The 2-B word thus produced can be sent to a host computer through a serial or parallel interface for further processing. To demonstrate the concept, a 16-channel interface has been described in a hardware description language and implemented on a complex programmable logic device. Measurement of two different capacitive pressure sensors developed in-house reveals frequency sensitivity values of $-$ 252.1 and $-$ 9.54 Hz/fF, which are in good agreement with the expected values derived by the analytic relations.