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Re: gEDA-user: High speed decoupling




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