The CS5516/CS5520 bridge-measurement A/D converters can be configured for precise measurement of resistance using a ratiometric resistance measurement technique. Figure 1 illustrates the CS5516 16-bit A/D converter used as a digitizer for a platinum RTD. The RTD is excited with a 250 mA current generated by the LM334 programmable current source. The 1N457 diode offers some first order temperature compensation to the current source, but the exact value and temperature coefficient of the current source isn’t important because the current is used in a ratiometric measurement configuration.