Re: noise question

Gerhard Hoffmann <dk4xp@arcor.de> wrote:

Am 16.07.24 um 05:29 schrieb Phil Hobbs:

Gerhard Hoffmann <dk4xp@arcor.de> wrote:

Am 15.07.24 um 20:04 schrieb john larkin:

On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
 

On 7/15/24 18:09, john larkin wrote:

On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
 

On 7/15/24 16:30, john larkin wrote:

 
<sniiip>
 

If you want nonlinear noise, you need Keysight's Advanced Design System
or such. Be prepared to a 5 or 6 digit price tag, depending on options.
The keyword is harmonic balance simulator.
 
 

 
 
Nah.  The LTspice noise() and white() functions give you time-domain noise,
with uniform or Gaussian amplitude statistics, and are good enough for many
things.
 
If you want separate voltage and current noise contributions, you can use a
voltage controlled current source.
 
To keep the complexity down, you need to do a little analysis to figure out
what the dominant noise sources are going to be, so that you can just model
those.

 
That assumes that oscillators are mostly linear, but they aren't.

No, it doesn’t. It’s the normal .tran simulation, not .noise or .ac.

Switching on a really linear oscillator would imply an explosion
soon after power on.So there must be a large scale non-linearity
to limit the growth.

Try it sometime. It works fine, as long as you scale and offset the
argument reasonably thoughtfully, to get the right bandwidth and enough
independent runs for good statistics.

Using white() or random() as part of a bv or bi expression will let you
model the changes in the noise with bias.

 
There are even proposals that say that there is an optimum point
in the cycle to inject all the feedback for best phase noise.
 
<
https://people.engr.tamu.edu/spalermo/ecen620/general_pn_theory_hajimiri_jssc_1998.pdf
    >
(and books on it)
 
Our ex-regular Kevin Aylward, WardenOf The King's Ale
<  https://www.kevinaylward.co.uk/    > has written fiercely
against that but people like Rubiola and U.L.Rohde seem to buy it.
 
interesting:   <  https://rubiola.org/   >
 
 

Sure, oscillator theory is fun.  Try looking into the math of injection
locking, if you like that sort of thing—it’s full of bifurcations and
strange attractors and limit cycles and stuff.

Most of the time I try to be relentlessly practical, but often fail. ;)

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics