Understanding Smart Sensors - Nomads.usp

Getting Sensor Information Into the MCU 834.3.1 Integrated Passive ElementsA sensor with precisely trimmed offset, full-scale span, and temperature compensationcan simplify the calibration procedure of the sensor and signal conditioningcircuitry. Figure 4.10 shows a pressure sensor with integrated resistorstrimmed to meet specifications that are possible in the semiconductor processflow. The low-TCR resistors are laser-trimmed with a 5-mm-diameter pulsedlaser beam [21]. Factors that affect the trim accuracy include the variability ofthe resistance of the deposited thin-film metal resistors, the annealing cycle forstress relief, and the sheet resistance. Process control allows the trimmed productto be extremely repeatable and provides high volume and high yield. Thatsmall amount of integration simplifies subsequent amplification circuitry, asthe circuits in Figure 4.1 and Figure 4.2 demonstrated. It also allows the sensorto be applied to a number of applications and with varied supply voltages.Figure 4.10 Photomicrograph of micromachined piezoresistive pressure sensor with integratedresistor network for zero offset, span, and temperature compensation.