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Understanding Smart Sensors - Nomads.usp

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Mechatronics and Sensing Systems 267The displays communicate information from the machine to the operator.Currently, active matrix LCDs are the dominant technology, but flat panel displaysand an emerging technology called field emission displays are potentialreplacements in several areas. Field emission displays produce light using coloredphosphors. They do not need complicated, power-consuming backlightsand filters, and almost all light is visible to the user. In addition, no power isconsumed by pixels in the off state. A field emission display consists of an arrayof microtips that are micromachined into a substrate. Metal, silicon, and diamondare being investigated for the microtips. One approach that uses MEMStechnology and silicon as the backplane has been analyzed for its potential to becost competitive versus other approaches [18]. The display is an array of fieldemitters on 0.9-mm centers used to provide a phase grating. The phase gratingis operated by electrically controlling the mechanical positions of the gratingelements to modulate the diffraction of light. The evaluation showed thisMEMS approach to be promising because it uses a simpler process and half theMEMS-masking steps of digital micromirrors (see Section 9.3.5). Successfulimplementation of this or any other CMOS-based imaging approach beinginvestigated for displays will provide additional possibilities for a sensor-tooperatorinterface.11.5.3 System Voltage Transients, Electrostatic Discharge, andElectromagnetic InterferenceSurviving voltage transients, ESD, and EMI are common application requirements,especially in the automotive environment. The ability to withstand aload dump is the prime factor in defining the voltage capability of semiconductordevices used in automotive applications. The load-dump transient is ahigh-voltage (>100V in an unsuppressed system), high-energy transient generatedby disconnecting the battery from the alternator when the engine rpm ishigh and the alternator is generating a high-level output. Techniques of handlingload dump include: (1) squelching the energy from an excessively highvoltage input (>60V) by turning on an active clamp until the energy decays(few hundreds of milliseconds) and (2) designing the output devices to withstandhigh voltage without turning on. The latter approach is done with anincrease in the resistance of each output device and therefore causes morepower dissipation under normal operating conditions. That technique must beused for high-voltage (>100V) pulses to avoid excessive power dissipation duringthe load dump. A third alternative uses the circuitry in the smart-powerdevice to turn the output on for a period of time (about 80 ms) when an overvoltageoccurs. The input is time filtered before sampling to determine if thegate drain clamp should be turned on again [2].

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