XTR105: typically achieving a 40:1 improvement in linearity

Hi Amy,

the datasheet of XTR105 and this appnote contains useful information:

2251.slyt442.pdf

Kai

Hi Amy,

Thanks Kai for presenting the application note!

Here is another ppt slides. If you need additional help, please let us know. 

5504.OPA188 2-wire analog linearization 09162022.TSC

https://www.ti.com/lit/ug/tidu433/tidu433.pdf?ts=1663340022589&ref_url=https%253A%252F%252Fwww.google.com%252F

If this is about the RTD measurement, please also see the link below. 

https://static5.arrow.com/pdfs/2013/11/24/3/19/23/744/txn_/manual/slau520.pdf

Best, 

Raymond

Hi Amy,

it should be noted that the method of positive feedback is used for the linearization here. You can nicely see this in the schematic shown by Raymond: The positive feddback is provided by R5 which is connected from the output of OPAmp to the +input (!) of OPAmp. I emphasize this here, because it's seldom explained in the appnotes that a positive feedback is used for the linearization.

Positive feedback is highly unusual because in the most linear OPAmp circuits only a negative feedback is used. Negative feedback stabilizes and linearizes a circuit. But positive feedback has the tendency of destabilizing an OPAmp circuit. Happily only a very small dose of positive feedback is necessary here to carry out the linearization and this does not result in stability issues in the very most cases. Nevertheless, the designer should have an eye on eventual stability issues.

There's another OPAmp circuit which uses positive feedback and which is known to have serious stability issues, the "Howland current pump". Howland current pumps have to be very carefully compensated to assure stable performance, especially if the load is complex.

Kai