Re: gEDA-user: ngspice shot noise

[Dan McMahill <dan@xxxxxxxxxxxx>]

Karel Kulhavy wrote:
> On Wed, Sep 28, 2005 at 08:17:24AM -0400, Dan McMahill wrote:
>
> > Karel Kulhavy wrote:
> >
> > > Hello
> > >
> > > Does ngspice noise model also work for operation of BJT with extremely
> > > small collector current?
> > >
> > > I got an idea to make low-noise amplifier by taking some 25GHz
> > > transistor and powering it with so small collector current that its
> > > transition frequency would drop down to 300MHz and then using it in
> > > Ronja preamplifier instead of 2N3904. As second or even first stage
> > > of the preamp.
> >
> > Why use an RF transistor?  The only reason I'd see for this is if 
> > thermal noise due to base resistance were your limiting factor.
>
>
> Because only RF transistor has transition frequency of 25GHz.

Fight, but you said you were going to use this where a 2N3904 would have 
enough speed so why do you need a 25 GHz Ft?  Also you said you were 
going to run at a current level low enough to drop the Ft down to 300 MHz.

-Dan