A remote junction temperature sensor (RJS) such as the TMP411 is useful because the device itself does not have to be close to the temperature measurement point of interest. This is important as oftentimes this may be an embedded processor. The RJS interfaces with either a diode or a transistor whose base-emitter voltage is proportional to the junction temperature in question.
To ensure an optimal connection from the remote sensor (i.e. diode or transistor), it is very important to make sure that spike noise from the processor does not couple in to the VBE/VD measurement, otherwise it will create a large temperature measurement error at the output. This can be done by adding some series RC filtering or ferrite beads; however, a best approach always includes a twisted, shielded pair with the shield grounded as close to the TMP411 as possible. The added series resistance will not affect the accuracy of the measurement as RJS devices have a series resistance correction mode that makes them immune to series R up to 3k ohms. Note that simply placing a large capacitor across the inputs (i.e. 1000pF) with no series resistance can actually be a worse approach as the capacitor will act as a sample-and-hold element which will cause a voltage error that will affect the temperature measurement.
Lastly, since RJS devices such as the TMP411 use a 4 current measurement scheme to calculate temperature, this makes the measurement immune to Seebeck (thermocouple) induction at the connection of the RJS to the diode on a processor PCB. If a small amount of mimatched voltage is induced at these solder connections, this will appear as an offset that will subtract out of the temperature calculation peformed by the internal ADC in the TMP411.
--Matt
