On 1/9/20 5:38 PM, Lifespeed wrote:
Hi Time Nuts,
I have a need for a low phase noise, noise floor and noise figure amplifier
at 400MHz. I have tried some off-the-shelf 50 ohm amplifiers, the best of
which degrades phase noise by a couple dB. I'm working with a signal with
-172dBc/Hz PN, so not much tolerance for degradation here. The input signal
level is only 3dBm, so noise figure still matters as well. I'm looking for
15dB gain, 16dBm P1. The residual phase noise would have to be better than
-180dBc/Hz, and I would probably operate the amplifier slightly compressed.
So you've tried something like the minicircuits CMA-5043? 18dB gain,
0.75 dB NF, P1dB 18dBm
They've got a whole raft of 0.5dB NF with 20+ dB gain, P1dB in the 17-19
dBm range - SAV-331, SAV-541, etc.
From the graphs, the NF is down around 0.3 dB below 500 MHz, if you
keep it reasonably cool (25C.. +85 the NF goes up)
If you need lower than that, I can ask around about discrete designs.
There's some group in Norway that is using FETs from Switzerland and
getting L band noise temps in the single digit Kelvin range. (without
cryocooling). I don't know if it would go down to UHF and hold that
performance
Any suggestions on topologies, transistors, white papers, etc? I'm
considering the NXP BFU590Q silicon bipolar transistor, which I have used in
a transformer feedback configuration at 100MHz with less than -180dBc/Hz PN.
But this topology doesn't appear practical for 400MHz due to the difficulty
maintaining a high collector impedance at that frequency with a transformer.
Nor do I need to control the gain, which is one of the features of the
transformer-feedback topology. I was thinking about common emitter with
inductive emitter degeneration. Not sure cascode is right for this UHF
application.
Lifespeed
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