低功耗解決方案地址傳感器的激勵要求

　　有源傳感器，需要激發產生可測量的輸出，工程師可以把多種選擇提供所需的電流或電壓水平。從簡單的基于運放的勵磁電路到高度集成的多功能集成電路，可供選擇的設備包括一系列設備，包括線性技術、微芯片技術和德克薩斯儀器等。

　　隨著人們對物聯網的興趣越來越大，傳感器子系統構成了許多預計將在薄膜電池和能量收集技術上運行多年的設計的核心。可靠的測量，但是，基于許多傳感器的電阻，如熱敏電阻、電阻溫度檢測器（RTD），應變計，和其他需要激發一個電流源或電壓源產生的電輸出。

　　An excitation current source output voltage of an RTD is directly proportional to the device‘s resistance. Although the use of high-excitation current would suggest larger voltage output， RTD resistance increases as its temperature rises from the higher current. Conversely， thermistor resistance drops as its temperature rises from similar self-heating effects. Beyond those types， other transducers such as Hall-Effect sensors， exhibit performance characteristics that vary significantly with applied excitation. As a result， active sensors typically require excitation maintained within strict limits to ensure reliable measurement with minimal nonlinearity.

　　Engineers can build simple excitation circuits using an available current-source IC， such as the Texas Instruments REF200， and a basic op amp， such as the TI OPA188 （Figure 1）。 With this approach， engineers can use two matched excitation sources produced by the current-source IC to adjust the op amp’s output voltage to zero at the low end of the desired sensor-measurement range.