A Closed-Loop Capacitance to Pulse-Width Converter for Single Element Capacitive Sensors

A novel closed-loop capacitance-to-pulse width converter (CPC) suitable for single element capacitive sensors that use sinusoidal excitation is presented in this paper. Its operation is realized using a new configuration based on a simple, yet effective, auto-balancing scheme. The hardware prototype of the proposed CPC is relatively less complex to implement than those presented so far in the literature. It provides a quasi-digital output at a high update rate. Additionally, the output is insensitive to parasitic capacitances of the sensor. The output possesses high linearity, with respect to change in the sensor capacitance, ranging +/-5 pF, with a nominal capacitance as high as 200 pF. It exhibits a maximum non-linearity error of 0.061% FS. The output of the prototype has a resolution of 13.31 bits. Also, its response time for a step-change in the sensor capacitance is about 13 ms. This sophisticated and inexpensive closed-loop CPC is a perfect fit as an interfacing circuit for single element capacitive sensors.

[1]  Xiujun Li,et al.  A novel interface circuit for grounded capacitive sensors with feedforward-based active shielding , 2008 .

[2]  Candid Reig,et al.  A Capacitance-to-Time Converter-Based Electronic Interface for Differential Capacitive Sensors , 2019 .

[3]  Boby George,et al.  A novel capacitance-to-digital converter for capacitive sensors with AC excitation , 2013 .

[4]  Manel Gasulla,et al.  Analysis of power supply interference effects on quasi-digital sensors , 2005 .

[5]  H. Zangl,et al.  A Novel Seat Occupancy Detection System based on Capacitive Sensing , 2008, 2008 IEEE Instrumentation and Measurement Technology Conference.

[6]  Tarikul Islam,et al.  A time domain bridge-based impedance measurement technique for wide-range lossy capacitive sensors , 2015 .

[7]  Vincenzo Stornelli,et al.  Autobalancing Analog Front End for Full-Range Differential Capacitive Sensing , 2018, IEEE Transactions on Instrumentation and Measurement.

[8]  Hiranmay Saha,et al.  A hygrometer comprising a porous silicon humidity sensor with phase-detection electronics , 2003 .

[9]  Trond Ytterdal,et al.  Low power OTA-less I-V-converter with single-ended to differential conversion for capacitive sensor interfaces , 2013, 2013 European Conference on Circuit Theory and Design (ECCTD).

[10]  Yifan Wang,et al.  Three dimensional touchless tracking of objects using integrated capacitive sensors , 2012, IEEE Transactions on Consumer Electronics.

[11]  Larry K. Baxter,et al.  Capacitive Sensors: Design and Applications , 1996 .

[12]  Boby George,et al.  An Improved Closed-Loop Switched Capacitor Capacitance-to-Frequency Converter and Its Evaluation , 2018, IEEE Transactions on Instrumentation and Measurement.

[13]  Nan-Chyuan Tsai,et al.  Air-Gap Detection Circuit Using Equivalent Capacitive Changes for Inductive Micromotor , 2015, IEEE Sensors Journal.

[14]  Yuan Meng,et al.  A Technique for Improving the Linear Operating Range for a Relative Phase Delay Capacitive Sensor Interface Circuit , 2016, IEEE Transactions on Instrumentation and Measurement.

[15]  Boby George,et al.  A simple analog front-end circuit for grounded capacitive sensors with offset capacitance , 2013, 2013 IEEE International Instrumentation and Measurement Technology Conference (I2MTC).

[16]  Z. Ignjatovic,et al.  An interface circuit for measuring capacitance changes based upon capacitance-to-duty cycle (CDC) converter , 2005, IEEE Sensors Journal.

[17]  Sheroz Khan,et al.  Experimental evaluation of agricultural biomass flow sensing behaviour using capacitive technique , 2013 .

[18]  Satish Chandra Bera,et al.  A Flow Measurement Technique Using a Noncontact Capacitance-Type Orifice Transducer for a Conducting Liquid , 2012, IEEE Transactions on Instrumentation and Measurement.

[19]  Weileun Fang,et al.  Poly-Si Based Two-Axis Differential Capacitive-Sensing Accelerometer , 2012, IEEE Sensors Journal.

[20]  Boby George,et al.  A Wide-Range Capacitive Sensor for Linear and Angular Displacement Measurement , 2017, IEEE Transactions on Industrial Electronics.

[21]  Kwang-Hyun Baek,et al.  Single Chip Dual Plate Capacitive Proximity Sensor With High Noise Immunity , 2014, IEEE Sensors Journal.

[22]  Heinz Woern,et al.  A tactile proximity sensor , 2010, 2010 IEEE Sensors.