When I use Pnoise analysis with noise type "timedomain" for a simple circuit (attached), I find the time domain value of output noise current through Vpulse is different with theoretical value sqrt(4KTG).

If doing Pnoise analysis with noise type "source", the PSD of output noise current is theoretical value  4KTG.

What does the noise value given by time domain Pnoise analysis represent?

-JC

Frank

Thanks for reply

I don't think there is aliasing or folding effect in the above circuit , because the thermal noise generated by the conductance is not modulated, neither the signal path from noise to output (Vpulse) is modulated.

Maybe I don't show clearly in the above circuit, which consists of a periodic pulse voltage source without noise and a resistor with the option "isnoisy=yes".

I have read that Ken's paper roughly but I haven't got the answer yet. I will read again carefully.

-JC

Frank:

Thanks a lot! You are totally right. By simluation I found SpectreRF includes this frequency aliasing effect itself.

So I think due to this behavior of PNOISE timedomain analysis I should be very carefull to choose a proper probe to observe noise otherwise the noise obsvered may be not the real one!

-JC