Sougata Kumar Kar

Tunable Square-Wave Generator for Integrated Sensor Applications

An Operational Transconductance Amplifier (OTA) based square-wave and clock generator with independent control over amplitude and frequency has been presented in this paper. Two out of phase square-waves along with rail to rail clocks are generated which are suitable for integrated sensor applications. Both amplitude and frequency of the waveform generator can be controlled independently by tuning the bias currents of the OTAs. These bias currents are controlled by two highly linear tuning OTAs. The complete circuit is implemented fully on-chip in UMC 0.18 μm CMOS process technology making it possible for integration with micro-sensing devices. The measured results show wide sweep capability of amplitude from 280 mVpp to 1 Vpp and frequency from 120 kHz to 900 kHz approximately with good linearity. This generator is suitable for integrated capacitive and resistive sensors and other instrumentation applications.

Effect of voltage induced electrostatic forces on MEMS capacitive accelerometer

In this paper the effect of electrostatic forces due to applied excitation voltage on MEMS capacitive accelerometer has been presented. A set of parallel plates often termed as combs or fingers along with a proof mass and a set of spring constitute the basic structure of a capacitive accelerometer. Some of the fingers are fixed while others are movable. The proof mass moves so that the movable fingers attached with it with applied acceleration. This movement changes the gap between the fixed and movable fingers and capacitance between the fixed and movable fingers changes which is measured through proper electronic circuitry for electrical output. A few numbers of fingers are also included in the structure for self test purpose, called as actuation fingers. This type of structure is often tested electro-statically by applying external voltage signal to the actuation fingers. This external voltage on the actuation fingers generates electrostatic force which causes the proof mass along with the movable fingers attached with it to move. In this paper the effect of applied voltage and the electrostatic force caused by it has been analyzed. The nature of the displacement of the proof mass has also been described. In the electrostatic analysis semi double frequency component is observed when the structure is actuated with an external electrical voltage.

Systematic Development of Integrated Capacitance Measurement System With Sensitivity Tuning

Modern sensor systems integrate microelectromechanical system (MEMS)-based sensors with signal conditioning circuits. MEMS sensors are fabricated through micromachining technology, which is relatively new compared with the integrated circuit technology, used since last few decades to fabricate circuits. As a result, these microsensors experience significant variation after fabrication. Besides, packaging of the sensors and integration with the circuit are also nontrivial as the sensors are of micrometer dimensions and they may have movable structures. In this paper, we have developed an integrated capacitance measurement system with a fully on-chip signal conditioning circuit. A systematic method of integration and testing with a silicon-on-insulator (SOI) MEMS capacitive accelerometer sensor is also presented. The signal conditioning circuit incorporates an array of on-chip capacitors to nullify the sensor capacitance mismatch and a tunable square-wave generator to tune the sensitivity of the system to cope up with the variations after fabrication of the devices. The complete circuit is designed and fabricated in United Microelectronics Corporation 0.18-

A Differential Output Interfacing ASIC for Integrated Capacitive Sensors

\mu \text{m}

Design methodology of closed loop MEMS capacitive accelerometers based on ΣΔ modulation technique

CMOS process technology. This circuit is integrated with an SOI MEMS sensor structure and various test methods are discussed. The integrated system is then mounted on a vibrating shaker along with a reference accelerometer and the measurement results are provided.

Design, integration and performance analysis of ΣΔ ADC for capacitive sensor interfacing

In this paper, we have proposed an input interfacing scheme with differential output for integrated capacitive sensor applications. In the proposed scheme, the front-end interfacing is based on switched capacitor charge amplifier configuration using a fully differential operational transconductance amplifier and one differential capacitive sensor arrangement which provides differential output with minimum number of circuit components. In the back end, a sigma–delta (

SOI MEMS based over-sampling accelerometer design with ΔΣ output

\Sigma \Delta

A highly linear CMOS transconductance amplifier in 180 nm process technology

) modulator is integrated for modulated digital output. The signal conditioning circuit also includes gain programmability by selecting proper feedback capacitor and mismatch cancellation between the sensing capacitors through on-chip capacitors array. The complete application specific integrated circuit (ASIC) is designed and fabricated in United Microelectronics Corporation (UMC)

Testing of MEMS capacitive accelerometer structure through electro-static actuation

0.18-\mu \text{m}

Linearity improvement of source degenerated transconductance amplifiers

CMOS process technology. The fabricated ASIC is then integrated with a silicon-on-insulator microelectromechnical systems capacitive accelerometer to test and characterize the performance of the proposed scheme. The measured result shows that the sensitivity of the proposed circuit can be varied from 200 to 900 mV/g by changing the feedback capacitor. The integrated system is also tested with electrostatic actuation as well as with a vibrating shaker and the measurement results are presented.