[time-nuts] Low Phase Noise Amplifiers

[lifespeed at claybuccellato.com]

-----Original Message-----
From: time-nuts <time-nuts-bounces at 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 at lists.febo.com>; Charles Clark <af8z at 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