Re: [time-nuts] Using the LT3042
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 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.
Re: [time-nuts] Using the LT3042
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.
Re: [time-nuts] Using the LT3042
FWIW for the 10MHz distribution amplifier I have been using LT1963 (40 uVrms in 10Hz to 100kHz) which is about 40x worse than the LT3042 spec of 0.8 uVrms in 10Hz to 100kHz. With decent op-amps I think the distribution-amp performance is limited by the op-amp noise and thermal noise in the resistors - I wouldn't expect the residual phase/amplitude noise to improve at all with a better LDO like the LT3042 - but ofcourse I haven't tried this :) The LT3042 spot noise spec of 2nV/sqrt(Hz) corresponds to Johnson noise of a 250 Ohm resistor at room-temperature (if my spreadsheet-calc is right..) - so I guess if one has circuits that are already optimized/limited by supply voltage noise at that level then moving to the LT3042 makes sense. AW On Wed, Jul 10, 2019 at 12:02 PM Perry Sandeen via time-nuts < time-nuts@lists.febo.com> wrote: > Yo Bubba Dudes!, > The LT3042 seems to be a wonderful part. But having learned a long time > ago the it wasn't wise to gold plate a Yugo, so when are there diminishing > returns? > For example I have several HP 10811 oscillators. one is in a HP5335a > counter that I'd like to make as stable as reasonably possible. Another > HP10811 needs a power supply. Also several Lucent XO OCXO's. > So where is it practical to hack for better results and when do you use > some not -as -wonderful regulator chips that come in a much easier to use > dip package for a power supply upgrade? > Regards, > Perrier > > > > > > ___ > 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.
Re: [time-nuts] Using the LT3042
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. Bruce > On 10 July 2019 at 18:18 Perry Sandeen via time-nuts > wrote: > > > Yo Bubba Dudes!, > The LT3042 seems to be a wonderful part. But having learned a long time ago > the it wasn't wise to gold plate a Yugo, so when are there diminishing > returns? > For example I have several HP 10811 oscillators. one is in a HP5335a counter > that I'd like to make as stable as reasonably possible. Another HP10811 needs > a power supply. Also several Lucent XO OCXO's. > So where is it practical to hack for better results and when do you use some > not -as -wonderful regulator chips that come in a much easier to use dip > package for a power supply upgrade? > Regards, > Perrier > > > > > > ___ > 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.
[time-nuts] Using the LT3042
Yo Bubba Dudes!, The LT3042 seems to be a wonderful part. But having learned a long time ago the it wasn't wise to gold plate a Yugo, so when are there diminishing returns? For example I have several HP 10811 oscillators. one is in a HP5335a counter that I'd like to make as stable as reasonably possible. Another HP10811 needs a power supply. Also several Lucent XO OCXO's. So where is it practical to hack for better results and when do you use some not -as -wonderful regulator chips that come in a much easier to use dip package for a power supply upgrade? Regards, Perrier ___ 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.
