# Ultralow Noise Tester: 9V Battery vs 7805 vs LTZ1000

Started by April 13, 2022
```Marco Reps has an interesting article on low noise amplifiers:

Ultralow Noise Tester: 9V Battery vs. 7805 vs. LTZ1000

- uses ADA4523: \$3.030 Mouser, Digikey, 4.2 nV/sqrt(Hz), RRIO, 100pA Ib

Cross-correlation would  improve  noise floor. Hard to  get  down to
Gerhard's level, but maybe doable.

1. Here is a brief explanation of how cross-correlation works:
"Understanding Phase Noise - the Cross Correlation Method"

2. 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"

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.

3. 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.

4. 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.

https://holzworth.com/Portals/0/HA7062C_Web_Datasheet.pdf

5. 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

https://www.mrmonett.com/pdfs/2015-IFCS-Rohde-Oscillator-noise.pdf

--
MRM
```
```On Thursday, April 14, 2022 at 3:02:14 AM UTC+10, Mike Monett wrote:

<snip>

https://www.analog.com/en/parametricsearch/11010#/p4007=300n|2u

https://www.analog.com/media/en/technical-documentation/data-sheets/ltc6655-6655ln.pdf

It's quieter than even the LTZ1000. And quite a lot cheaper. I suspect that the LTZ1000 parts are only being made for the legacy market, where it's cheaper to pay through the nose for a drop-in replacement than it would be to change the board to accommodate something newer and marginally better.

--
Bill Sloman, Sydney
```