Re: gEDA-user: LED in reverse

[Karel Kulhavy <clock@xxxxxxxxxxxxx>]

On Tue, Nov 21, 2006 at 11:02:51AM +0100, Wojciech Kazubski wrote:
> >
> > 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?
> Gold reduces lifetime of carriers and thus increase switching speed of the 
> device. If the junction is forward biased then it is filled with free 
> minority carriers (electrons or holes). If the junction is rebiased to 
> reverse bias, carries from deleption layer have to be removed. Without gold 
> doping they have to be removed trough external circuit and the diode conducts 
> for a moment (up to miliseconds for sislicon - see switching characteristis 
> of the diode). Gold makes minority carriers to recombine fast and less charge 
> is stored during forward bias. Such diode recovers quickly at turn off.
> In saturated transistor B-C get forward biased and charge is stored here.
> >
> > My application is noise-critical between 1MHz and 10MHz. Would BC547C be
> > better than 2N3904?  I assume it's not a switching transistor.
> >
> Rather use BC549 or BC550, they have tighter spec on noise.
> Or use BF240 if gain has to be higher.
> PNP transistors can have lower noise due to lower base resistance.

Does the gold increase only 1/f noise or also the broadband (white) noise?

CL<
> 
> Wojciech Kazubski
> 
> 
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