Hi,
I have a test case, where I have simulated a simple circuit containing 50ohm port driving 50ohm load followed by VCVS driving an RC-circuit.
If I set the noise_fmax parameter to a higher frequency than my Fs/2, the noise levels increase in the spectrum and SNR decreases. I assume that this is because of noise aliasing due to higher noise_fmax than fits to the spectrum. Furthermore, since the output is bandwidth limited, the noise does not increase so much. As a result, if I calculate noose figure NF=SNR_INPUT-SNR_OUTPUT, at some point, if I increase noise_fmax enough, I get negative NF.
So the question is, should the noise_fmax parameter always be set to Fs/2, when sampling the output? I use stobeonly-option to output only values defined by strobeperiod.
Thanks,
Jere