Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
Subject: Re: Aylward, Engelhardt: Noise in a transient sim?
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Date: Fri, 18 Oct 2002 16:38:20 +0100
NNTP-Posting-Date: Fri, 18 Oct 2002 16:38:21 BST
"Mike" wrote in message
> "Kevin Aylward" wrote in message
> > I have not gotten round to actually making one yet, but it can be
> > by making a simple circuit model. One way is to construct a little
> > chaotic generator. The buzz words being Fractals, Mandelbrot etc.
> A random noise generator is one thing, but I'm talking about a noise
> simulation that would include device noise. So, for example, a
> FET amplifier would include the Gaussian noise contributions of the
> and FET as well as the flicker noise from the FET.
> Since the FET noise is a function of the bias point, modeling it with
> discrete voltage and current sources is difficult unless the bias
> stays fixed. Increase the circuit complexity to several hundred FETs,
> the discrete approach is fairly intractable, even without considering
> points. Even for some simple circuits like a ring oscillator, the
> transistors are moving through a range of bias points during each
> the noise produced by each device is thus time varying.
I think I see what your getting at. You mean effectively having the real
noise of a device that is usually only given in the frequency domain, be
given in the time domain. This would seem to be a bit tricky, and
probably more involved then what one really requires. i.e. I can't be
bothered with all that effort:-)
The deal is though, you can get a pretty good estimate by worst casing
and erroring on the high side. I have simulated, e.g. VCO's and simple
put various signals on the power supply to see the effect. Its often the
case that it is extraneous noise that is the issue with high performance
designs, such that the normal circuit noise is not that relevant. If you
have digital switching in analogue circuits, it difficult to predict
just what noise is going to be anyway.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.