Understanding Smart Sensors - Nomads.usp

Using MCUs/DSPs to Increase Sensor IQ 107AddressgenerationunitOn-chipperipheralshost, SSI, SCIparallel I/OInternal databus switchand bitmanipulationunitProgramROM3.75K × 24YDBXDBPDBGDBX MemoryRAM256×24ROM256×24Y MemoryRAM256×24ROM256×24ExternaladdressbusswitchBuscontrollerExternaldata busswitchAddressPort A7DataClockgeneratorProgramaddressgeneratorProgramdecodegeneratorProgram controllerPrograminterruptcontrollerData ALU24×24÷ 56 56-bit MACtwo 56-bit accumulatorsFigure 5.6 24-bit DSP architecture.table or performing a calculation determines the response time of the sensorinput to the MCU/DSP portion of the system. That can be the limiting factorto initiating a change to the output in an MCU/DSP-controlled system.A control-sensor combination can implement an electronically programmabletrim as an alternative to laser trimming. However, all trimming and calibrationprocesses for a sensor require some form of data conversion by theMCU or DSP. The time it takes to perform those conversions by mathematicalcalculations or get data from a lookup table must be within the control system’sability to respond to the sensed input. In the application, real-time trimmingcan be implemented to allow adaptive control at the sensor level. That willimprove the accuracy of a sensor that has drifted after some time in operation.5.5 Techniques and Systems ConsiderationsIncreased precision can be obtained for sensors by characterizing devices overtemperature and pressure (or acceleration, force, and so forth) and storing correctionalgorithms in MCU memory. The MCU can convert the measurementto display different units (e.g., psi, kPa, mmHg, or inches of water for pressuremeasurements). Other techniques use the MCU’s capability to improve