Understanding Smart Sensors - Nomads.usp

94 Understanding Smart Sensorsintegrated chip utilizing “core” microprocessor cells combined with analog,memory, and additional logic functions can address specific sensing requirementssuch as fluid-level sensing. Mixed-signal ASICs combine analog withdigital capability.FPGAs and field-programmable analog arrays (FPAA), analog versions ofFPGAs, are attractive as sensor interfaces because they can minimize developmenttime and can be reconfigured after they have been in service. Both theFPGA and FPAA use a front-end circuit design program [1]. A circuit design istransferred to the FPGA (or FPAA) by either downloading converted serial datadirectly to the on-chip static random access memory (RAM) in the FPGA or toserial erasable programmable ROM (EPROM). A digital core incorporated inthe FPGA design gives it the same kind of computing capability as an MCUwith the advantages of field programmability. FPGAs are especially useful whenrapid circuit prototyping and flexibility are required.The term system on a chip (SOC) is frequently used to describe a highlyintegrated circuit, ASIC, MCU, or DSP that incorporates considerably morehardware options than previously available versions. These chips frequentlyincorporate application-specific software that is closely linked to the hardwareon the chip. These chips include a large and increasing amount of the systemand reduce the total chip count. In only the simpler systems are they actuallythe whole system. That is especially true with the sensor portion of the system.The added complexity of adding the sensor to the SOC makes a sensor systemon a chip far more difficult—and much more expensive—than available alternatives.(Chapter 14 provides more detail on the sensor SOC.)5.1.2 Logic RequirementsThe shift of the logic requirements from a centralized computer to nodes indecentralized systems is creating the need for smart sensors. Sensor-drivenprocess control systems that eliminate human operators and increase the precisionof the process will play an important role in the manufacturing of thesemiconductors that control them. A new architecture and interface have beenproposed by researchers at the University of Michigan to address this application[2]. Figure 5.1 shows the block diagram of the key elements of that proposal.Amplification and A/D conversion were discussed in Chapter 4, and thecommunications interface is covered in Chapter 7. This chapter uses existingMCU and DSP products to demonstrate the remaining elements. Othersystem components that can be obtained with an MCU or a DSP are alsodiscussed.