Understanding Smart Sensors - Nomads.usp

104 Understanding Smart SensorsJ1850VPWCANJ1850PWMInter-integratedcircuitCOPCANPORTMRSCISPIA/D converterD/A converterDTNF decoderVFD displayWatch-dogtimerSwitched capacitorfiltersCHASSISCPUROMROMROM68HC05C468HC05C4RAMAuto rangingLED driverAuto zeroingLCD driverDTMFencoderLDMOSdriversSeriesregulatorShuntregulatorLow-poweroscillatorFigure 5.5 Custom MCU and various building blocks.meet a specific customer requirement. The last case, “design to order,” is usedfor only a small portion of the total design. The preferred approach utilizeshand-packed, highly optimized, and field-tested circuits to achieve short designcycle time, first-time success, and low end-product cost.The CSIC approach minimizes—in some cases eliminates—nonrecurringengineering costs, and it allows a custom chip to be designed that can cost lessthan $1 for some units. In many cases, one of the existing designs is acceptableto provide a “semicustom” solution without requiring a new design. Thenumber of available MCU options and a methodology that allows quick customizationof MCUs have been in place for several years to address the specificrequirements of various applications.5.4 DSP ControlDSPs have hardware arithmetic capability that allows the real-time execution offeedback filter algorithms. In contrast, MCUs use lookup tables to approximatefilter algorithms with inherent limitations of flexibility and accuracy. A typicalDSP can execute instructions in less than 100 ns. That capability allows a peakexecution rate of 20 MIPS (millions of instructions per second), which is 10 to20 times the performance of conventional MCUs. DSPs are often rated in millionof operations per second (MOPS). The MOPS rating is several times the