Re: [Ngspice-users] About noise analysis

[Kevin Z. <kev...@gm...>]

Hi Akshay,

On 3/10/22 12:18 PM, Akshay Kulkarni wrote:
> This is Akshay Kulkarni and I am currently working on PLL with ngspice.
> 
> I was getting the phase noise at the output of PLL and I was not really 
> sure if the noise analysis that is present in the ngspice can perform that.
> 
> My question is -> Does noise analysis in ngspice give out phase noise?

No, it does not.

'noise' analysis in ngspice is small-signal AC noise analysis. Imagine 
that ngspice computes equivalent noise sources for each component than 
contributes noise (e.g. resistors, transistors) and computes how much 
noise goes to the output, then sums them all up. This noise analysis is 
applicable to amplifiers.

To simulate phase noise, you would need a simulator that supports it 
(spectre from Cadence, for example). In such simulators, you compute a 
periodic operating point using shooting Newton ('pss') or harmonic 
balance ('hb'), then compute the periodic noise ('pnoise').

Regards,
Kevin