3 Conclusion

Three-wire configurations are a common and effective way to remove the errors introduced by lead resistance to RTD measurements. However, three-wire systems require a pair of well-matched current sources to effectively remove errors. A simple method to create these matched current sources is to use a monolithic pair of N-JFETs such as the JFE2325. The JFE2325 includes two, well-matched, JFET devices on the same die inside of an extremely small 0.8mm × 1mm package. Because the two JFETs share the same silicon area, their parameters match each other far better than discrete single JFETs. Furthermore, adding a source resistor to the JFETs introduces negative feedback which reduces variation in the output current due to changes in the JFET parameters. This approach delivers two current sources with exceptional matching at a very low cost, small solution size, and able to operate over a wide range of power supply voltages.