利用ADS1216,ADS1217,和ADS1218进行温度测量---外文文献译文和原文.docVIP

附录1 英文论文 Measuring Temperature with the ADS1216, ADS1217, or ADS1218 By Saeid Jannesari and Jim Todsen OVERVIEW The ADS1216, ADS1217, and the ADS1218 are integrated systems for single-chip high-resolution measurements. Included among the analog features is a diode inside the input MUX. Coupled with the high-resolution Analog-to-Digital Converter (ADC), the diode provides a convenient means of measuring temperature. This application discusses some of the considerations and techniques in using this diode. The last section presents some measurement data to help illustrate the performance that can be expected. MEASURING TEMPERATURE WITH A DIODE To understand how to use the diode to measure temperature, it helps to briefly review some of the key equations. For a good, detailed description of the diode’s operation, see The PN Junction Diode by Gerold W. Neudeck. The current through a diode (IDIODE) can be approximated by: ① where IS is a constant that depends on the area of the diode and its temperature among other things;VDIODE is the forward voltage across the diode, n is a constant usually close to 1, and VT is the thermal voltage given by: ② where K is Boltzman’s constant, T is the absolute temperature (K) and q is the charge of an electron. Figure 1 shows the typical plot of IDIODE versus VDIODE (the ADS1216’s diode was used in this and all other plots). Now consider Equation 1’s temperature-dependent terms. Equation 2 gives VT’s dependence; it’s proportional to the absolute temperature. The other temperature-dependent term, IS, roughly doubles every 5℃. Together, these two terms produce a net change in the voltage across the diode of approximately –2mV/℃ for a diode biased with a constant current. This relationship can be used to measure temperature by simply measuring the voltage across the diode, just bias the diode with a constant current and measure the diode’s voltage. Figure 2 shows the diod