Large signal SNR with transient noise analysis

Hello everyone,

i'm trying to calculate SNR for an amplification circuit with photodiode input. I can't simulate small signal noise, because the photodiode's modell isn't even capable of AC simulation. So i thought of at least calculating the large signal SNR by simulating transient response to a sinus input with activated transient noise.


Up to the simulation everything works fine and i obtain the noisy output curves i wanted. But what output expression has to be set, to calculate the SNR? I tried a few things:

- Fourier Transformation on the output voltage and "spectrumMeas" applied on this. But it only seems to work for data converters (states the "help" description), not amplifiers.

- Doing two transient simulations - one noisy and the other not - with the intention to subtract the resulting waveforms (result is the "noise function") and divide the noisy output curve by the "noise function". But i didn't found a way to subtract the two plots, because they have one different parameter - i have them both in one test environment by applying a variable to "Fmax" in transient noise. I also tried to create a combinatorial expression by putting the simulation without noise in a second test environment and do something like (VT("/VoltageWithNoise") - calcVal("VoltageWithoutNoise" "TestWithoutNoise")), resulting in an evaluation error.


Does anybody know how to get the large signal SNR of an amplification circuit with transient noise analysis or can help me with my attempts? I use IC6.1.6.500.07 and ADEXL.

Regards,

Johannes.