Michele Dei

A Low-Power 2-D Wind Sensor Based on Integrated Flow Meters

A 2-D wind sensor, based on microelectromechanical systems (MEMS) flow sensors, is presented. The device consists of a cylinder with a channel network connecting the internal flow sensors with the lateral surface. The pressure distribution developed by the wind on the cylinders surface is thus converted into two air flows from which, due to the special channel configuration, wind speed and direction can be unequivocally determined. Since the MEMS devices are located in the channels, their fragile sensing structures are protected from direct exposure to the wind. Performance estimation based on literature data of pressure distributions indicates that the approach is applicable to a wide wind velocity range. The feasibility of the idea is supported by measurements performed on a prototype.

A Low-Power Interface for Capacitive Sensors With PWM Output and Intrinsic Low Pass Characteristic

A compact, low power interface for capacitive sensors, is described. The output signal is a pulse width modulated (PWM) signal, where the pulse duration is linearly proportional to the sensor differential capacitance. The original conversion approach consists in stimulating the sensor capacitor with a triangular-like voltage waveform in order to obtain a square-like current waveform, which is subsequently demodulated and integrated over a clock period. The charge obtained in this way is then converted into the output pulse duration by an approach that includes an intrinsic tunable low pass function. The main non idealities are thoroughly investigated in order to provide useful design indications and evaluate the actual potentialities of the proposed circuit. The theoretical predictions are compared with experimental results obtained with a prototype, designed and fabricated using 0.32 μm CMOS devices from the BCD6s process of STMicroelectroncs. The prototype occupies a total area of 1025× 515 mm2 and is marked by a power consuption of 84 μW. The input capacitance range is 0-256 fF, with a resolution of 0.8 fF and a temperature sensitivity of 300 ppm/°C.

Smart Flow Sensor With On-Chip CMOS Interface Performing Offset and Pressure Effect Compensation

A single-chip smart flow sensor based on a thermal principle is presented. The device is fabricated through a commercial complementary metal-oxide-semiconductor (CMOS) process combined with a postprocessing procedure. A configurable electronic interface performing signal reading and nonideality compensation is integrated with the sensing structures on the same chip. The interface implements recently proposed approaches to offset and pressure effect compensation. Detailed experimental results are presented demonstrating correct operation of the proposed microsystem.

An Offset Compensation Method With Low Residual Drift for Integrated Thermal Flow Sensors

A new offset compensation approach for integrated thermal flow meters is described. The method is based on micromachined differential flow sensing structures with the heater split into two identical and symmetrical sections. The power unbalance between the two heaters is used to compensate the intrinsic sensor offset. The effectiveness of the approach is proven by means of experiments performed on micro flow meters fabricated by postprocessing chips produced with a commercial microelectronic process. The tests were devoted to demonstrate the robustness of the offset compensation with respect to variation of both the gas temperature and type.

A Method to Compensate the Pressure Sensitivity of Integrated Thermal Flow Sensors

Microelectromechanical systems (MEMS)-based thermal flow sensors are considerably more sensitive to pressure than traditional macroscopic devices. This fact, due to the micrometric dimensions of MEMS sensors, limits the accuracy of the latter when large pressure variations cannot be avoided. In this work, we propose an original pressure compensation method that exploits the same signals produced by the flow sensor to detect the pressure variations and to control the heater power according to a closed loop approach. A first-order model is used to explain the operating principle and optimize the parameters of the feedback loop. A readout interface based on the proposed approach, has been built and applied to MEMS thermal flow sensors. Experimental results are presented to demonstrate the effectiveness of the method.

Design of CMOS chopper amplifiers for thermal sensor interfacing

An analytical approach to the design of compact CMOS chopper amplifiers for integrated thermoelectric sensors is presented. The impact of the high resistance and low signal bandwidth of thermopile sources on the design is illustrated. The proposed approach, regarding the precision vs noise tradeoff, is applied to the design of a practical prototype, using a commercial process. Accurate electrical simulations are provided to confirm the effectiveness of the proposed design methodology.

A four quadrant analog multiplier based on a novel CMOS linear current divider

An analog, Gilbert-like CMOS multiplier, based on a novel linear current divider, is described. The divider uses a cascade of two differential pairs to produce a linear dependence between the tail current and the two output currents. A numerical algorithm has been implemented to find the optimum sizing of the active devices in order to compensate for the deviation from the ideal MOSFET square law. The results of low frequency measurements performed on a prototype, designed with CMOS devices from the STMicroelectronic process BCD6s, are shown.

A four quadrant CMOS analog multiplier based on the non ideal MOSFET I–V characteristics

This paper concerns an analog CMOS multiplier based on a novel approach to compensate for non idealities of the MOSFET square law approximation. A numerical algorithm has been implemented to find the optimum sizing of the active devices, starting from the process characteristics. The effectiveness of the proposed configuration has been demonstrated by means of electrical simulations performed on a prototype cell, designed using 0.32 mum - 3.3 V CMOS devices from the STMicroelectronic process BCD6s.

Single chip sensing of multiple gas flows

The fabrication and experimental characterization of a thermal flow meter, capable of detecting and measuring two independent gas flows with a single chip, is described. The device is based on a 4times4 mm2 silicon chip, where a series of differential micro-anemometers have been integrated together with standard electronic components by means of post-processing techniques. The innovative aspect of the sensor is the use of a plastic adapter, thermally bonded to the chip, to convey the gas flow only to the areas where the sensors are located. The use of this inexpensive packaging procedure to include different sensing structures in distinct flow channels is demonstrated.

A New Principle for Environment Resistant Integrated Anemometers

Development of compact, inexpensive and low power sensors is the key step towards the application of wireless sensor networks in real scenarios. In this work we propose a new approach for monitoring wind direction and speed using integrated flow meters, included into a protecting cylinder. An original channel geometry drilled through the cylinder produces a flow that depends on the wind direction according to a cosine law, facilitating wind direction estimation. The effectiveness of the approach is proven by means of measurements performed on a prototype.