[time-nuts] TNS-BUF update

[Bruce Griffiths]

Without the benefit of agressive low pass filtering the noise of an LT3042 at 10Hz is at least an order of magnitude worse than that of an unfiltered LED for the same output voltage.
The noise of Nitride passivated LEDs degrades significantly with aging and there is a strong correlation between LED noise and its quality / aging degradation.  

http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p10.pdf

Bruce
> On 20 August 2018 at 03:42 Gerhard Hoffmann <dk4xp at arcor.de> wrote:
> 
> 
> 
> 
> Am 19.08.2018 um 14:43 schrieb Bruce Griffiths:
> > Yes, I looked at the plots and I see exactly what I described.
> > 2nV/rtHz at frequencies somewhat above the reference current source output RC filter, rising to a high value at frequencies below the current source output filter pole.
> > This is an inherent property of the architecture.
> 
> I really don't know how you come to that conclusion. Even the HLMP-6000 
> needs more than
> 100 Hz to be better than the 3042 in its standard data sheet circuit, 
> without extra filtering
> provided, and the LED delivers only half the DC voltage, another 6 dB.
> 
> 'Ordinary' LEDs from Toshiba or Osram(ex Siemens) are 20 to 30 db worse, 
> and they are
> quality parts, not unknown junk box parts.
> Their 1/f corner is - OMG!!!11! -  the plot goes only to 1 MHz!
> 
> Postulating superior LED  performance at 1Hz from that is quite venturesome.
> LEDs are good in comparison to el cheapo bandgaps and high voltage "Zeners",
> but they cannot do magic.
> 
> 
> And please don't say, it's the light. The measurements are made in a box 
> in a box in a box
> to handle the pV noise densities. My preamps are now at 70 pV/rtHz and 
> there is a
> chopper in statu nascendi at 100 pV sub- 0.1 Hz. Yes, I see the noise 
> of  the 0.6 Ohm switches.
> 
> But I need a better FFT analyzer now. A working SPI driver @ 
> 1Mtransfers/sec for the
> BeagleBoneBlack would do.
> 
> cheers, Gerhard
> 
> 
> ps. I'm also interested in that time travel movie.
> 
> 
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