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Subject: Re: Determining bjt noise parameters for Spice models?
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Date: Mon, 16 Dec 2002 16:59:31 -0500
NNTP-Posting-Date: Mon, 16 Dec 2002 16:32:39 EST
"A.Iakovlev" wrote in message news:3DFE3F2C.6BF365DD@worldonline.fr...
> "John S. Dyson" wrote:
> > It is probably best to consider both the en and in type effects, and not
> > prejudicially pronounce 'rbb and 1/f' as being the key.
> > Rather, I tend to prefer these ideas for midband:
> > en^2 = 4 * k * T * rbb(eff) + 2 * q * Ic * re^2
> > in^2 = 2 * q * Ib
> Of what order should the Spice RE be expected? It is also very often missing from the models...
> If comparable to RB, it would contribute comparable thermal noise (voltage term) as well...
Oh, sorry -- I didn't make it clear: the re that I was using above is mostly
made up from the 0.025/Ic (at room temperature.) This isn't a physical (or
parasitic) resistor, but is of the dynamic sort. There is some physical resistance,
but that shouldn't be much of an issue at currents that are used for low noise.
> > When using rbb as a criteria for selecting a low noise device,
> And low RE?
You certainly want a low physical RE (as a parasitic or contact resistance),
but the re value is predominantly the dynamic resistance.