A novel general purpose current mode oscillating circuit for the read-out of capacitive sensors

In this paper we present a novel general purpose current mode (CM) solution for the interfacing of capacitive sensors. The designed circuit, which utilizes only two second generation current conveyors (CCIIs) as active blocks, allows to detect, through a capacitance-to-time conversion (C-T), capacitive values as well as their variations (also lower than 1pF) both in a small and a wide range. Its main operation is based on a current differentiation, instead of voltage integration, typical of interfaces developed in the voltage-mode approach. The proposed circuit, which does not need any initial calibration, has been designed as integrated solution at transistor level in a standard CMOS 0.35µm technology. Waiting for the chip fabrication, preliminary experimental results have been performed through a discrete-component board and sample capacitors and resistors. Both simulation and experimental results have shown low percentage errors and a good agreement with theoretical expectations for more than five frequency decades. The system sensitivity has been set to about 1.8µs/pF.

[1]  Vincenzo Stornelli,et al.  An integrated improved CCII topology for resistive sensor application , 2006 .

[2]  Chua-Chin Wang,et al.  An Implantable Long-term Bladder Urine Pressure Measurement System with a 1-atm Canceling Instrumentation Amplifier , 2007, 2007 IEEE International Symposium on Circuits and Systems.

[3]  Janusz Bryzek,et al.  Advances in State-of-the-Art in Smart Sensor Signal Conditioning , 1997 .

[4]  G. Ferri,et al.  Low voltage integrated astable multivibrator based on a single CCII , 2007, 2007 Ph.D Research in Microelectronics and Electronics Conference.

[5]  Giuseppe Fern,et al.  Low voltage low power CMOS front-ends for capacitive sensors , 1997 .

[6]  G.K. Fedder,et al.  A low-noise low-offset capacitive sensing amplifier for a 50-/spl mu/g//spl radic/Hz monolithic CMOS MEMS accelerometer , 2004, IEEE Journal of Solid-State Circuits.

[7]  Franco Maloberti,et al.  Smart sensor interfaces , 1996, 1996 IEEE International Symposium on Circuits and Systems. Circuits and Systems Connecting the World. ISCAS 96.

[8]  Josep Samitier,et al.  Mechanical sensors integrated in a commercial CMOS technology , 1997 .

[9]  K. Smith,et al.  A second-generation current conveyor and its applications , 1970, IEEE Transactions on Circuit Theory.

[10]  Gaetano Palumbo,et al.  1.5-V CMOS CCII+ with high current-driving capability , 2003 .

[11]  Christofer Toumazou,et al.  Micropower front-end interface for differential-capacitive sensor systems , 2008 .

[12]  Ted Smith,et al.  Low-Power Sensor Interfaces , 1997 .

[13]  Giuseppe Ferri,et al.  Low-Voltage Low-Power CMOS Current Conveyors , 2003 .

[14]  G. Ferri.  Low voltage low power CMOS front-ends for capacitive sensors , 1997, 1997 2nd IEEE-CAS Region 8 Workshop on Analog and Mixed IC Design.

[15]  M. Knite,et al.  Polyisoprene-carbon black nanocomposites as tensile strain and pressure sensor materials , 2004 .

[16]  Johan H. Huijsing,et al.  Integrated smart sensors , 1992 .

[17]  Kenneth C. Smith,et al.  The current conveyor—A new circuit building block , 1968 .

[18]  W. Ko,et al.  An optically powered wireless telemetry module for high-temperature MEMS sensing and communication , 2004, Journal of Microelectromechanical Systems.

[19]  G. Fedder,et al.  A Low-Noise Low-Offset Capacitive Sensing Amplifier for a 50-g = Hz Monolithic CMOS MEMS Accelerometer , 2004 .

[20]  Hassan Elwan,et al.  Low-voltage low-power CMOS current conveyors , 1997 .

[21]  Robert Puers,et al.  Capacitive sensors: When and how to use them☆ , 1993 .

[22]  Vincenzo Stornelli,et al.  CCII-BASED OSCILLATOR FOR SENSOR INTERFACE , 2008 .

[23]  Willy Sansen,et al.  A capacitive pressure sensor with low impedance output and active suppression of parasitic effects , 1990 .

[24]  Gordon W. Roberts,et al.  The current conveyor: history, progress and new results , 1990 .

[25]  Jean-Paul Bardyn,et al.  A very low-noise CMOS preamplifier for capacitive sensors , 1993 .

[26]  Timothy G. Constandinou,et al.  A micropower front-end interface for differential-capacitive sensor systems , 2008, 2008 IEEE International Symposium on Circuits and Systems.

[27]  Jean-Paul Bardyn,et al.  A High Temperature Micropower Capacitive Pressure Sensor Interface Circuit , 1997 .