Re: gEDA-user: Spice noise analysis

["Harold D. Skank" <skank54@xxxxxxxxx>]

Thank you for your advice.  I did get your procedure to work, though I'm
somewhat in doubt as to how to interpret the results.  Basically the
onoise_spectrum had about the shape I expected, but the flat central
region was about 130 femptoVolts whereas the data sheet listed something
like 2 to 3 nanovolts noise (at the input).  What about this?

	Harold Skank

On Thu, 2005-08-04 at 22:31 -0400, John Doty wrote:
> In ngspice/tclspice use something like:
> 
> noise v(vout) v3 dec 1 100k 10meg 1
> 
> v(out) is the point for output noise assesment
> v3 is the source relative to which input noise is calculated
> dec means do it by decades
> 1 means one point per decade
> 100k means start at 100 kHz
> 10meg means end at 10 MHz
> 1 means record source contibutions at each point
> 
> Then do "print all": that'll tell you the values, in
> V^2/Hz. inoise_spectrum is the total input referred noise, onoise_spectrum
> is the total output referred noise, and the other onoise* are the noise
> contributions broken down by elementary component and physical noise
> source. To get the total from a subcircuit, you need to add up all its
> component noise contributions, or (probably easier here) subtract
> contributions from components you aren't assessing. It may also be useful
> to set resistor temps to zero for resistors whose noise you don't want to
> assess.
> 
> To just plot input or output noise, leave out the last argument, and throw
> in more points:
> 
> noise v(vout) v3 dec 10 100k 10meg
> 
> Then you'll only get inoise_spectrum and onoise_spectrum.
> 
> Beware that this is linear analysis around your DC operating point.
> Dynamic noise sources associated with changing operating points are not
> evaluated. You can get some of these by careful use of initial conditions
> to evalate noise at particular operating points (say, if your Shottkys
> turn on at some particular phase of input signal and make shot noise), but
> you'll have to then assess the system effect of such modulated noise by
> other means. SPICE can't handle things like clock jitter and capacitor
> switching ("kTC") noise at all, so in general SPICE noise analysis is only
> part of a total noise assessment.
> 
> John Doty          "You can't confuse me, that's my job."
> MIT-related mail:                       jpd@xxxxxxxxxxxxx
> Other mail:                             jpd@xxxxxxxxxxxxx
> 
> On Thu, 4 Aug 2005, Harold D. Skank wrote:
> 
> > People,
> > 
> > Attached below is the SPICE file for an Analog Devices amplifier with a
> > pair of crossed Shottky diodes in front for amplifier protection.  I
> > need to run an noise analysis to assess the noise contribution from the
> > Analog Devices amplifier.  How do I do this?
> > 
> > 	Harold Skank
> > 
>