Marco Reps has an interesting article on low noise amplifiers:
Ultralow Noise Tester: 9V Battery vs. 7805 vs. LTZ1000
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- uses ADA4523: $3.030 Mouser, Digikey, 4.2 nV/sqrt(Hz), RRIO, 100pA Ib
- Datasheet
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Cross-correlation would improve noise floor. Hard to get down to Gerhard's level, but maybe doable.- Here is a brief explanation of how cross-correlation works: "Understanding Phase Noise - the Cross Correlation Method"
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- The benefit of cross-correlation depends on how long you are willing to wait. From
"TSP #162 Tutorial on Theory, Characterization & Measurement Techniques of Phase Noise"
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each 5db of improvement requires an order of magnitude increase in the number of correlations.dB 5 10 15 20 25 30 35 40 N 10 100 1000 1E4 1E5 1E6 1e7 1e8
So going from -180dBc/Hz to 220dBc/Hz would require 1e8 correlations.
- Nobody would wait that long. But how many correlations do you need?
A commonly accepted figure is your measurement noise floor has to be at least 10 dB below the noise you are trying to measure. We could pad that by 5 db, which would require
15 / 5 = 3
1e3 = 1000 correlations. That is not too bad.
- It is interesting to note the Holsworth HA7062C Phase Noise Analyzer goes to a maximum of 1024 cross-correlations. 100 correlations (-10dB) takes 7 min, 9s at 10 MHz.
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- Finally, "Frequency Signal Source's PN (Phase Noise) Measurements Challenges and Uncertainty", by Ulrich L. Rohde, has some very important information on cross-correlation errors. This file is at
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