I thought this discussion was closed when @bordodynov posted a screen where “Fast (less accurate) Math” is deselect as a solution.
Just to ensure everyone know exact reason why this option gives two different results, here is an explanation
In Qspice HELP > Simulator, it mentioned two simulator executables which are QSPICE64.exe and QSPICE80.exe
In Preference, you can decide simulation to run with 64 or 80.
- Select “Fast (less accurate) Math” : use QSPICE64.exe
- Deselect “Fast (less accurate) Math” : use QSPICE80.exe
Mike Engelhardt explained the different between QSPICE64 and QSPICE80 in this post : QSPICE80.exe uses 80 bit math in critical sections
Running qspice from command line? - QSPICE - Qorvo Tech Forum
It seems that this circuit with large number and require 80 bit math to handle it.
So, nothing goes wrong in here, as higher bit math normally rarely needed and in default Qspice use Qspice64.exe.
