A Low-Cost Sensor and A/D Interface

摘要

Who needs a separate voltage reference? Simply maintain the proper interface between your sensor's output and the ADC's reference input, and you can reduce costs while improving performance. Most sensors are inherently analog and must have their signals digitized by an A/D converter (ADC) before they can be used in today's electronic systems. Although this means adding two components to your design for one job, you can exploit the ratiometric characteristics of many sensors and ADCs to improve accuracy while simultaneously reducing overall component count, lowering cost, and reducing board space. The automotive industry has taken advantage of these techniques for years: By specifying both sensors and ADCs that are ratiometric to the supply voltage, automotive designers eliminate the need for accurate voltage references. Less common is the use of similar techniques with current-driven sensors and single-element resistive sensors such as RTDs. A shared trait of these circuits is that the sensitivity of the ADC varies with temperature or supply voltage, but the combination of the ADC and sensor input is quite stable. To fully appreciate the benefits of using the supply voltage as your reference, you need to understand some sensor and ADC basics.