Understanding Smart Sensors - Nomads.usp

68 Understanding Smart Sensorsin a 0.5-psi sensor with 7 mV/V/psi [22]. The larger area does not compromiseruggedness, but it does increase the cost of the sensor.3.7.3 Combined Solution: Micromachining and MicroelectronicsA more recent solution to increasing the sensitivity uses the combined capabilityof a low-pressure sensor and a microcontroller. Figure 3.9 shows the blockdiagram [23]. The microcontroller provides a signal to pulse the sensor with ahigher supply voltage. The microcontroller also provides signal averaging fornoise reduction and samples the supply voltage to reject sensor output variationsdue to power supply variations. An important factor for sensors makingvery low pressure measurements is stress isolation for the package. A piston-fitpackage for the unit used in this circuit allows 40 mV/Pa with a 15V source.3.8 SummaryThis chapter showed the distinct advantages that semiconductor sensors haveover mechanical predecessors. However, these sensors require additional effortto obtain their full benefits in systems. Semiconductor sensors draw fromLowpressuresensorSignalconditioningLow voltageinhibit8-bitMCUVppDoutDinSCLKSwitchingcircuitryCS5V±5%regulatorPowersupplyrejectioncircuitryFigure 3.9 Low-pressure sensor combined with MCU to achieve higher pressuresensitivity.