[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 Dana Whitlow
Sent: Saturday, January 11, 2020 8:28 AM
To: Discussion of precise time and frequency measurement
<time-nuts at lists.febo.com>
Subject: Re: [time-nuts] Low Phase Noise Amplifiers

FWIW, at the Arecibo Observatory all our cryogenic LNAs had bias stabilized
with active stabilizers based on opamps.  Since the opamps do not work at
~15K, bias connections to the drain and gate of the RF FETs were brought out
separately from the RF connections, and the opamp circuitry was at room
ambient temp.
This approach would nicely stabilize both drain DC voltage and drain current
over the whole temperature range from room ambient to 15K, which was handy
for testing and monitoring LNA behavior during cool-down, which takes
several hours (or more).

Dana
**************
Opamp stabilization is nice.  Do you have any idea of the residual phase
noise or broadband noise floor you were getting with this bias, or was that
not a figure of merit for the cryo LNAs?  Even though an opamp circuit can
be designed for low noise, probably large passive filtering components would
be required to tamp down the broadband noise.

Lifespeed