[time-nuts] Spice simulation of PSRR and phase noise

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Oct 22 16:58:40 EDT 2017

Hoi Attila

Since close in phase noise can result from up conversion of supply noise etc via circuit non linearities, using an AC analysis won't work.

Only transient simulation or perhaps analytical modelling of the various non linearities will provide accurate estimates of upconverted PN. If you use transient simulation techniques increasing the level of the various noise sources above the actual levels encountered in real circuits and then correcting the resultant PN back to the level that would be encountered in the actual circuit (using the results of analytical modelling) may be a useful way to reduce simulation time or at least overcome some of the challenges associated with accurately determining low level PN from a simulation.

There are some in the LTSpice Yahoo group attempting this but they seem way out of touch with the amount of simulation data required. I've provided them with the appropriate formulae to extract PN from the the amplitude spectra. At the moment they appear bogged down with some somewhat trivial peripheral issues.


>     On 23 October 2017 at 01:53 Attila Kinali <attila at kinali.ch> wrote:
>     Hi,
>     I have been looking into spice simulations of circuits, in particular
>     trying to extract PSRR and phase noise information. Unfortunatelly,
>     the obvious way of putting AC sources at the right places does not
>     work, as the (ideal) input signals are not small and drive the circuit
>     into non-linearities. Hence I have to do transient simulations.
>     But extracting PSRR and phase noise information out of a transient
>     simulation is cumbersome at best and takes a lot of simulation time
>     (we are talking about hours to days for simple circuits).
>     I am looking for guidelines and hints how to speed things up.
>     Maybe even being able to use standard DC and AC analysis for the
>     circuit instead of transient. Unfortunately, my google-foo was not
>     strong enough to find approriate documentation.
>     Does someone have any hints what I should read or search for?
>     Thanks in advance
>     Attila Kinali
>     --
>     It is upon moral qualities that a society is ultimately founded. All
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