A microsystem composed of a micromachined resistiveflow sensor and a signal conditioning CMOS IC is proposedfor biomedical applications. The device can be adapted to noninvasively monitor urinary dysfunctions in male patients. The flow sensor, thermally simulated with ANSYS, is based on the hot-film principle: A thin film of gold laid on a suspended micromachined siliconmembrane is heated while the fluid under test flows through the duct mounted above the membrane. The flow rate is sensed by measuring the temperature difference between two of the four polysilicon temperature sensors realized on the membrane.Simulations of the flow sensor with flow rates within 0.1–18 ml/s evidence a maximum temperature difference of 20 ◦C between the temperature sensors. Characterization of the fabricated flow sensor shows temperature coefficient of resistance (TCR) values of −1930 ppm/◦C for the polysilicon resistors, i.e., a resistance variation of about 4% at high flow rates. The CMOS readout designed for the flow sensor is a resistive bridge-to-duty cycle converter based on a relaxation oscillator. The digital output of the circuit is duty-cycle modulated by the change in resistance of the flow sensor’s elements. Experimental tests on the CMOS interface, conducted with a setup of 1% precision resistors, report a maximum nonlinearity below 0.9% and a resolution of 7 bits over the full range of 4% resistance variation. The CMOS integrated readout circuit, provided with a digital output, allows simple signal interfacing towards any standard PC for periodical data transfer and storage.
A Low Cost Micro-System for Non-Invasive Uroflowmetry
Massari, Nicola;Gottardi, Massimo;Simoni, Andrea;Margesin, Benno;Faes, Alessandro;Decarli, Massimiliano;Guarnieri, Vittorio
2006-01-01
Abstract
A microsystem composed of a micromachined resistiveflow sensor and a signal conditioning CMOS IC is proposedfor biomedical applications. The device can be adapted to noninvasively monitor urinary dysfunctions in male patients. The flow sensor, thermally simulated with ANSYS, is based on the hot-film principle: A thin film of gold laid on a suspended micromachined siliconmembrane is heated while the fluid under test flows through the duct mounted above the membrane. The flow rate is sensed by measuring the temperature difference between two of the four polysilicon temperature sensors realized on the membrane.Simulations of the flow sensor with flow rates within 0.1–18 ml/s evidence a maximum temperature difference of 20 ◦C between the temperature sensors. Characterization of the fabricated flow sensor shows temperature coefficient of resistance (TCR) values of −1930 ppm/◦C for the polysilicon resistors, i.e., a resistance variation of about 4% at high flow rates. The CMOS readout designed for the flow sensor is a resistive bridge-to-duty cycle converter based on a relaxation oscillator. The digital output of the circuit is duty-cycle modulated by the change in resistance of the flow sensor’s elements. Experimental tests on the CMOS interface, conducted with a setup of 1% precision resistors, report a maximum nonlinearity below 0.9% and a resolution of 7 bits over the full range of 4% resistance variation. The CMOS integrated readout circuit, provided with a digital output, allows simple signal interfacing towards any standard PC for periodical data transfer and storage.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
