[time-nuts] Using the LT3042

[Bruce Griffiths]

Those measurements don't go low enough in frequency to capture the very low frequency noise of the LT3042 which uses a noisy current source to produce a voltage drop in a resistor as the reference. At low enough frequencies the LT3042 is very noisy.  Low pass reference filters with milliHz or lower cutoff frequencies are usually impractical. 

Bruce
> On 10 July 2019 at 22:58 Gerhard Hoffmann <dk4xp at arcor.de> wrote:
> 
> 
> 
> Am 10.07.19 um 11:27 schrieb Bruce Griffiths:
> > Like virtually all low dropout regulator ICs the LT3042 is quite noisy at frequencies below its reference low pass filter high frequency cutoff. Some zener based references are considerably quieter in this region.
> 
> We had that already last year.
> 
> I have delivered measured curves that show that it's not true.
> 
> The trick of the LT3042 is that it's reference is not very noisy,
> 
> and there is NO VOLTAGE GAIN after the reference. Zener-based
> 
> reference diodes are _much_ worse, and the LT3042 can hold
> 
> the candle even to 2V7-Zeners and most LEDs.
> 
> You can filter the LT3042 reference quite heavily, and there is
> 
> a startup circuit so you do not have to wait too long for the output voltage
> 
> to become stable.
> 
> 
> common Regulators:
> 
> < 
> https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/ 
>      >
> 
> 
> Zeners: (Look at that awful super-precision ovenized LM399!)
> 
> < 
> https://www.flickr.com/photos/137684711@N07/24411798996/in/album-72157662535945536/ 
>      >
> 
> 
> LEDs:
> 
> < 
> https://www.flickr.com/photos/137684711@N07/24354944411/in/album-72157662535945536/ 
>      >
> 
> 
> King of the LEDs is hp/Avago/Broadcom HLMP6600, if it is still alive.
> 
> 
> I plan to repeat these measurements in the close future with a new 
> FET-based amplifier that
> 
> is not challenged by that stronger-than-1/f low frequency noise and that 
> can use cross correlation
> 
> additionally because of its missing noise current.
> 
> 
> regards, Gerhard.
> 
> 
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