-----Original Message----- From: time-nuts <time-nuts-boun...@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@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 _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
