Hello again
There is another thing I would like to understand about how the simulator works in this instance, but I'll keep it separated from the "buggy behaviour" I just wrote about.
From the Manuals, this is the relationship between NF calculation and other AC noise outputs:
(a little unfortunate typesetting here)
So the NF or its linear cousin F, rightfully, do not include the noise due to the load of the DUT, just that of the DUT itself and of the input source.
On the other hand, AC noise calculates the total noise at the output. Moreover, it does not give access to the NI component in the manual's screenshot, i.e. the output noise due to the load.
Since I absolutely want to be able to calculate "NF-like" quantities, but not always having voltage at the output, and I don't want to always depend on the NF calculation, I set out to find an "alternative" way to double-check the NF results.
To this end, I just then thought, in the first instance, to load my DUT with a noiseless resistor, so that the NI part above is automatically zero.
Given that I don't use the "noise separation" option, the noise summary shows (more or less) what I would expect: no trace of Rl:
Now, I have to say that "ext_file_noise" contributor still bothers me, but at least there's no other contributor beyond the input port and the transistor itself.
According to my understanding I should be able now to plot NF and to superimpose a curve to it, by just calculating textbook-like:
output_noise/(input_noise*gain²)
Because - following the manual - the gain is voltage and referred to the internal source of the port:
then the input noise of the source is simply 4*K*T*R (in voltage²) and the gain is just the gain coming out of the noise simulation.
However, when I do all this, I get a curve with a constant difference, and I don't know where this difference is coming from:
This difference is constant.
These are the definitions used for my version of NF:
Can anybody suggest what I might be missing here?
Thanks,
Michele