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).


利用ADS1216,ADS1217,和ADS1218進(jìn)行溫度測量
作者：Saeid Jannesari and Jim Todsen

綜 述
ADS1216,ADS1217,和ADS1218是一種單片集成高精度測溫系統(tǒng)。內(nèi)置的模擬特性一個(gè)重要的特點(diǎn)就是多路復(fù)用器(MUX)內(nèi)部集成了一個(gè)感溫二極管。這個(gè)二極管與A/D轉(zhuǎn)換器相連使之提供了一種便捷的測溫方式。這篇應(yīng)用報(bào)告主要討論的就是這只二極管在使用過程中需要注意的事項(xiàng)和技術(shù)。最后一節(jié)介紹一些測量數(shù)據(jù)以便于闡述其期望值。

利用二極管測溫
要想更好地理解二極管是如何測溫的，我們需要復(fù)習(xí)幾個(gè)重要的公式。欲了解詳細(xì)的二極管的工作過程請參考由Gerold W.Neudeck.編寫的《The PN Junction Diode》。流過二極管的電流可以近似地表示為：
式（1）
其中，IS是一個(gè)常量，其大小取決于二極管的區(qū)域以及與其相近的其它器件的溫度；VDIODE
是二極管兩端的電壓，n也是一個(gè)常量通常接近于1，VT代表熱電勢由以下公式給出：
式（2）
其中，K表示玻意爾常數(shù)，T表示絕對溫度（K）,q表示電荷電量。如圖1所示為