gEDA-user: TwoStageAmp example

[John Doty]

On Apr 4, 2007, at 10:33 PM, al davis wrote:

> On Tuesday 03 April 2007 22:46, John Doty wrote:
>> Yep. Of course what a low level digital video designer wants
>> is   *noise* analysis at a particular point in time. And a
>> simulator that could incorporate physical noise directly into
>> a transient analysis would really get my attention.
>
> Since you are doing digital, I guess your main concern is
> channel noise, not things like resistor noise.  Would a simple
> noise source fit your needs?

Well, of course the video comes in as analog!

>
> How about a NOISE variant of a voltage source?  (along with PWL,
> SIN, and so on)  It seems to me that a random number generator
> with some filtering would do the job.  Those source functions
> are plugins in gnucap, so it should be easy  to make another
> one for noise.  They work for other components too, not just
> sources.

It really needs to be built into the device models. Much of the point  
of a SPICE NOISE analysis is to be sure you haven't left out an  
important noise source in your pencil and paper noise analysis.

Of course, explicit noisy sources could be handy too, for noisy  
inputs, power supplies, etc.

SPICE NOISE analysis is like AC with a lot of sources. But it would  
also be useful to be able to do a noisy transient analysis. I think  
the tricky part there would be getting things to converge while still  
modeling important effects like switched-capacitor kTC noise.

>
> In almost spice syntax ..
> V123 (1 0) noise bandwidth=20k amplitude=5
>
> In verilog syntax ...
> noise_source #(.bandwidth(20k), .amplitude(5)) V123 (1, 0);
>
>
> How would you display the results?  I am thinking of the "eye
> diagram", which would require triggered retrace, like an
> oscilloscope.  I am not aware of any of our wave viewers that
> have this feature.

In the tricky cases it's not a simple matter of display. The  
simulator output needs a fair amount of post processing. Tools like  
AWK, C, and Mathematica come in handy, here.

>
>
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John Doty              Noqsi Aerospace, Ltd.
jpd at noqsi.com