Re: gEDA-user: LED in reverse

[Karel Kulhavy <clock@xxxxxxxxxxxxx>]

On Mon, Nov 20, 2006 at 10:17:52AM -0700, John Doty wrote:
> 
> On Nov 20, 2006, at 8:38 AM, Karel Kulhavy wrote:
> 
> >On Sun, Nov 19, 2006 at 09:20:53PM +0100, wk0 wrote:
> >>
> >>Some time ago i read the warning for RF transistors that reverse  
> >>biasing into
> >>breakdown of the E-B junction may significantly increase noise  
> >>figure.
> >
> >Does it increase the noise figure permanently or only temporarily?
> 
> Permanently.
> 
> >
> >What if I have a circuit with 2N3904 transistors with 5V break down  
> >and it has
> >12V power supply and on turn-on, a little current at 12V goes  
> >through the
> >junction the wrong way? Do I have to design my circuits to prevent  
> >that?
> 
> I wouldn't worry about it with a 2N3904. The RF transistors that have  
> this problem have relatively thin, lightly doped base regions making  
> them much more susceptible to damage. Indeed, from a noise figure  
> point of view the 2N3904 is *intentionally* damaged in manufacturing  
> by gold doping to improve saturated switching performance.

What happens when there are gold atoms? The electrons bouce against these
atoms and they produce noise in the process? Does these gold increase
only 1/f noise or also the broadband (white) noise?

My application is noise-critical between 1MHz and 10MHz. Would BC547C be better
than 2N3904?  I assume it's not a switching transistor.

CL<
> 
> John Doty              Noqsi Aerospace, Ltd.
> jpd@xxxxxxxxx
> 
> 
> 
> 
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