Hi Peter,

personally, when using ELDO, I tend to use the AC noise simulation and get the total noise through calculations. I find the noisetran result difficult to exploit.

In an SC circuit, I believe (at least) part of the noise contributions at frequencies above the filter cut-off may be folded back due to the sampling process. For this reason, I would set fmax to something (one decade?) above the amplifier cut-off frequency.

Paul

PS: there's a whole chapter on transient noise simulation in the Eldo user's manual.

Do you have access to SpectreRF? That would be a much better bet for simulating the noise in an SC filter. Transient noise analyses (and spectre can do this as well, since MMSIM60) suffer from the problems you've described if you want to make any kind of quantative measurement - you need to set the maximum frequency to something sensible (which results in rather short timesteps) and you need to simulate for a long time to get the averaging and to include flicker noise properly. So it's best for qualitative measurements (in my opinion) (i.e. did the change I made in my circuit improve things or make things worse) - and it's best to use something else (like pnoise, or tdnoise) if you can (i.e. if the circuit is periodic in nature, and the noise can be treated as small signal).

Regards,

Andrew.