Understanding Smart Sensors - Nomads.usp

Smart Sensor Basics 13edge of the right side of the diaphragm. The package used for that sensor(shown in the middle of the diaphragm with the actual chip inside) has six terminals.Only three terminals are required for the application; the other threeare used to access measurement points on the chip during the trim process andare not necessary for the sensor to function properly.A major advantage of integrated sensing and signal conditioning is theaddition of calibration through on-chip techniques, such as laser trimming ofthin-film resistors on the sensor die, and the subsequent ability to obtain partfor-partreplaceability at the component level. The amount of signal conditioningcan vary. For example, the addition of thin-film resistors and laser trimmingto the sensing element is all that is necessary to produce a calibrated andtemperature-compensated sensor for disposable blood pressure applications. Forlower volume applications, the requirement for unique transfer function or interfacecircuitry may not be cost effective. In those cases, the basic sensor with externalcircuitry is still the best choice. Eventually, the unique lower volumeapplications could also benefit from the advantages of integration.Sensing and integrated sensing (sensing plus signal conditioning) aresomewhat analogous to other mixed-signal processes that exist in semiconductors,especially in power and smart-power technology, that is, the output side ofthe control system. Today’s smart-power technologies integrate bipolar andCMOS circuitry with multiple power metal oxide semiconductor field effecttransistor (MOSFET) output devices. The process is more complex than a discretepower MOSFET, but the performance achieved by the combination oftechnologies provides a specific function, component reduction for increasedreliability, and space reduction for lower cost assemblies and more than justifiesthe higher processing cost. After a number of years of process and designimprovements, smart-power devices have established broad market acceptance,especially for custom designs. Similarly, smarter sensors that have their own signalconditioning circuitry onboard are in the early phases of market acceptanceand are approximately at the same stage of development as smart power was fiveto seven years ago. However, smart sensors may not have to be custom devicesto satisfy a large number of applications.New packages must be developed for smart sensors to accommodate theadditional connections for power, ground, output, diagnostics, and other featuresthat the combination of technologies can provide. Sensors have few, ifany, commonly accepted packages. Instead, each supplier provides a uniquepinout and form factor. The problem is exacerbated by the addition of morefeatures to sensors, either through integration or by the addition of circuitry.Prior to the era of sensor integration, products that combine technologyat the package level, rather than at the silicon level, have been the industrynorm. A hybrid or module solution has the advantage of using proven available