Re: gEDA-user: High speed decoupling

[John Doty <jpd@xxxxxxxxxxxxx>]

On Mar 13, 2006, at 2:06 AM, Karel Kulhavy wrote:

> On Sun, Mar 12, 2006 at 06:14:54PM -0700, John Doty wrote:
> > On Mar 12, 2006, at 3:59 AM, David Hart wrote:
> >
> > > I was particularly impressed in this webinar, and the subject of
> > > thermal
> > > noise generated by resistors in an analog circuit. I'd forgotten  
> > > that
> > > resistors with higher values contribute more thermal noise.
> >
> > Depends on whether noise voltage or current is the dominant effect in
> > that part of the circuit. Bipolar transistor current mirrors are
> > noisy, but adding large emitter resistors makes them quieter...
>
> What if you block the BE junction with a capacitor instead? Does it
> decrease the noise too?

Not sure what you mean here. Capacitor blocking the base maybe?  
Usually that increases output noise at low frequencies: noise current  
from the base produces a voltage across the cap that the transistor  
then amplifies.

John Doty              Noqsi Aerospace, Ltd.
jpd@xxxxxxxxxxxxx