A mass flow controller, based on an integrated flow
sensor and a thermally actuated solid state regulator, is presented.
The sensor is a miniaturized differential calorimeter obtained by
postprocessing a silicon chip fabricated by a standard microelectronic
process. The regulator consists in a microchannel etched
into the surface of a silicon substrate and sealed with a glass plate,
joined to the silicon die using anodic bonding. Flow regulation
is achieved by varying the channel temperature by means of a
chromium resistor. The two devices are connected in closed-loop
through a low noise—low offset electronic circuit. Experimental
data, demonstrating the effectiveness of the flow controller, are
presented. Limitations of the proposed approach and possible
improvements are discussed
This work describes a novel approach for interfacing capacitive sensors in the sub-pF range. The system generates a PWM signal with a linear relationship between the pulse duration and the sensor capacitance. The circuit exhibits intrinsic low sensitivity to temperature and process variations and is therefore an interesting solution when extremely wide operating temperature ranges are required. A detailed analysis of the noise characteristics, aimed to give indications about the circuit optimisation, is presented. The interface has been designed using the 0.35 µm BCD6 process of STMicroelectronics and tested by means of electrical simulations.
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