-----Original Message-----
From: time-nuts <time-nuts-boun...@lists.febo.com> On Behalf Of Richard (Rick)
Karlquist
Sent: Saturday, January 11, 2020 7:39 AM
To: Discussion of precise time and frequency measurement
<time-nuts@lists.febo.com>; Charles Clark <a...@earthlink.net>
Subject: Re: [time-nuts] Low Phase Noise Amplifiers
A VERY long time ago, it was discovered that simply degenerating a transistor
with an emitter resistor makes a worthwhile improvement in 1/f noise. I want
to say this was published in 1970 by Dick Baugh of HP but don't hold me to it.
Note that the resistor was NOT bypassed: it's purpose was RF feedback, and any
stabilization of bias current was incidental.
The resistor value was a few dozens of ohms. That is not enough to do anything
special in terms of stabilizing collector current.
In oscillators, a designer might want to use a high performance bias
stabilization scheme to minimize frequency drift (as opposed to noise).
Various publications out of NIST (Fred Walls, et al) recommend using a
transistor with high Ft vs the operating frequency to get low 1/f noise. This
becomes more important when working at 100 MHz vs 10 MHz.
As far as bias is concerned, the main emphasis seems to be on using a bias
scheme that doesn't ADD noise to the amplifier.
Rick N6RK
**************
Yes, while I am familiar with active bias and generally like the stabilization
I think you're correct that low noise bias will be key. Transistor ft, emitter
degeneration (inductive, I'm thinking), minimizing thermal noise from resistors
and impedance matching for low noise figure will all be important.
Lifespeed
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