Understanding Smart Sensors - Nomads.usp

12 Understanding Smart Sensorsuser to treat the sensor as a “black box” and easily design a complex controlsystem.The integrated sensor takes advantage of integrated temperature sensingto more closely track the temperature of the sensing element and compensatesfor the effects of temperature over the temperature range. By reducing thenumber of internal connections, the reliability of integrated sensors is inherentlybetter than a separate sensor and control circuit, even when the separatecomponents are manufactured using a thin-film ceramic substrate. For a fourterminalsensor element, a reduction from 23 to only 9 connections is possibleusing an integrated solution. Because the sensor provides the first informationto a control system, the reliability of that information is critical to the entiresystem’s reliability.Figure 1.8 is useful in analyzing the results of integrating the first twostages illustrated in Figure 1.7 to obtain the sensor portion of a level III system.Figure 1.8 is an enlarged view of a fully integrated piezoresistive pressure sensorwith the amplification and signal conditioning circuitry, including lasertrimmedresistors, located around the silicon diaphragm etched in the middleof the chip. The single piezoresistive element is one arm of the X that is near theFigure 1.8 Photomicrograph of pressure sensor die with packaged sensor over themicromachined diaphragm. (Courtesy of Motorola, Inc.)