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 <dk...@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. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
