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.step in LTspice XVII for OS X - plots show constant Vout

Maybe I'm doing something wrong, but I can't get the plots to show the change in Vout when R2 in the schematic is stepped. I can see the value of R2 being stepped in the plots, but Vout stays constant. Vout should change from 100 uV down to 1 uV as R2 is increased from min to max resistance. The CD Op point works OK (2nd and 3rd pics below). The 4th and 5th pics below show the .step issue. Does the .step function in the Mac version of LTSpice work? This is a pretty simple circuit. 

    1108.Pyrometer Preamp LTC1050.asc

Added actual schematic file Pyrometer Preamp LTC1050.asc
[edited by: pgoodwin at 3:46 PM (GMT 0) on 25 Jul 2020]
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  • you might also want to look at the LTC6244 datasheet for some really neat TIA circuits based on JFETs and op amps. This might improve your system level design. We have JFET models in LTspice - or you can import a third party model

  • thanks for the info. My particular application has a need for both very low Vos and low opamp bias currents. The ambient temperature of the ambient where this would reside is close to 80C. The particular photodiode being used was chosen for a particular wavelength bandwidth. Unfortunately the photodiode leakage resistance (R2 in my schematic) can drop down to 13K or so at that high temp. So the output gain vs Vos goes from 1.0 to 75. Delta Vout vs Ibias at the (-) input is Rfdbk * delta Ibias over temp. The other constrain on this system is that there's not much supply current available - the 6244 would be a challenge just for that purpose. JFET and CMOS input opamps are definitely the way to go.