Re: [time-nuts] Low Phase Noise Amplifiers
Lifespeed, The cryogenic amplifiers were used in very broadband situations (often hundreds of MHz BW) with "signals" that were basically noise. Most radio astronomy lies in the art of measuring very small *changes *in noise level, such as between pointing at an object of interest or pointing away from it at a known quiet spot in the nearby sky. So we are talking about radiometry, where the "Radiometer Equation" rules. In this game, the best results are had by using the widest possible RF/IF BW, then running the noise into a square law detector, then passing the output of the detector through a very low BW filter. I mention the above because I suspect it means that phase noise in the predetection part of the path has little of no effect (unless, of course, there is a strong signal lurking not far outside the IF passband). To my knowledge, we've never tried to measure phase noise of any of the cryogenic amplifiers. Our LNAs mostly have noise temperatures in the range of 2K to 3K, which is roughly 0.03 to 0.04 dB NF. Dana On Sun, Jan 12, 2020 at 3:33 PM wrote: > -Original Message- > From: time-nuts On Behalf Of Dana > Whitlow > Sent: Saturday, January 11, 2020 8:28 AM > To: Discussion of precise time and frequency measurement > > 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. > ___ 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.
Re: [time-nuts] Low Phase Noise Amplifiers
-Original Message- From: time-nuts On Behalf Of Dana Whitlow Sent: Saturday, January 11, 2020 8:28 AM To: Discussion of precise time and frequency measurement 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.
Re: [time-nuts] Low Phase Noise Amplifiers
-Original Message- From: time-nuts On Behalf Of Richard (Rick) Karlquist Sent: Saturday, January 11, 2020 7:39 AM To: Discussion of precise time and frequency measurement ; Charles Clark 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 ___ 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.
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 On Sat, Jan 11, 2020 at 9:40 AM Richard (Rick) Karlquist < rich...@karlquist.com> wrote: > 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 > > On 1/11/2020 6:36 AM, Charles Clark wrote: > > I wonder if adding active bias feedback around the RF transistor to > > reduce the low frequency current variations would help. This is the > > classic PNP bias scheme which can be applied to BJT's or FET's. I have > > used it to successfully improve the phase noise on oscillators. Details > > from T.T. Ha, or Gonzales books on Amplifiers. > > > > Chuck, AF8Z > > > > > > ___ > > 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. > > > > ___ > 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. > ___ 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.
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 On 1/11/2020 6:36 AM, Charles Clark wrote: I wonder if adding active bias feedback around the RF transistor to reduce the low frequency current variations would help. This is the classic PNP bias scheme which can be applied to BJT's or FET's. I have used it to successfully improve the phase noise on oscillators. Details from T.T. Ha, or Gonzales books on Amplifiers. Chuck, AF8Z ___ 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. ___ 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.
Re: [time-nuts] Low Phase Noise Amplifiers
Am 11.01.20 um 15:36 schrieb Charles Clark: I wonder if adding active bias feedback around the RF transistor to reduce the low frequency current variations would help. This is the classic PNP bias scheme which can be applied to BJT's or FET's. I have used it to successfully improve the phase noise on oscillators. Details from T.T. Ha, or Gonzales books on Amplifiers. ... and available as cheap SOT343 chip from Infineon: BCR400W < https://www.infineon.com/dgdl/Infineon-BCR400W-DS-v01_01-en.pdf?fileId=db3a30431400ef68011407e93d8601a1 > I vaguely remember that its use in an oscillator has been patented. =8-() cheers, Gerhard ___ 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.
[time-nuts] Low Phase Noise Amplifiers
I wonder if adding active bias feedback around the RF transistor to reduce the low frequency current variations would help. This is the classic PNP bias scheme which can be applied to BJT's or FET's. I have used it to successfully improve the phase noise on oscillators. Details from T.T. Ha, or Gonzales books on Amplifiers. Chuck, AF8Z ___ 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.
