Yes, the short hand I like to use is 4 nV*sqrt(R/1000). 2 nV/rthz off a bandgap is pretty darn impressive, that includes a delta vbe gained up ~10x.
On Wed, Dec 7, 2016 at 7:03 PM Bob Camp <[email protected]> wrote: > Hi > > > > Just for reference, KTB in 1 Hz at 50 ohms is roughly 0.9 nV at room > > temperature. The previously mentioned 2 nV is equivalent to about 250 ohms. > > > > Bob > > > > > On Dec 7, 2016, at 6:58 PM, Scott Stobbe <[email protected]> > wrote: > > > > > > You can buy opamps off the shelf with an input referred noise less than a > > > 50 ohm resistor to build up a preamp (of course you can build up > something > > > even lower with discretes, but then it's a time commitment over a basic > > > opamp preamp) > > > > > > Even if your regulator is low noise if it's running with low phase margin > > > you can get noise peaking. > > > > > > On Wed, Dec 7, 2016 at 3:06 PM Van Horn, David < > > > [email protected]> wrote: > > > > > >> > > >> > > >> I replaced the original caps, and I added caps, I substituted good > > >> Jonhansen RF caps, and Tanceram caps. > > >> > > >> No help at all. > > >> > > >> > > >> > > >> The layout and routing is as good as I could do, and the only > improvement > > >> I could see possible would be to move one cap closer to the reg. > > >> > > >> The difference would be less than the tolerance of part placement on the > > >> existing pads. > > >> > > >> > > >> > > >> Fortunately this isn't a critical piece of equipment, but I want it > > >> working RIGHT before I put it back in service. > > >> > > >> It's a custom receiver for 457 kHz. > > >> > > >> > > >> > > >> > > >> > > >> -----Original Message----- > > >> > > >> From: time-nuts [mailto:[email protected]] On Behalf Of > Graham / > > >> KE9H > > >> > > >> Sent: Wednesday, December 7, 2016 10:41 AM > > >> > > >> To: Discussion of precise time and frequency measurement > > >> > > >> Subject: Re: [time-nuts] Totally unrelated, but.. > > >> > > >> > > >> > > >> Remember that the internal Voltage reference in the original three > > >> terminal regulator designs is a Zener. > > >> > > >> (Zeners are also useful as RF white noise sources.) The regulator is > > >> generally an amplifier with DC feedback. > > >> > > >> If you look at the application notes on the early regulators, they > require > > >> capacitors to ground on both the input and outputs. > > >> > > >> If these capacitors are missing, or too low in value, or not good > > >> capacitors at RF frequencies, then the Zener noise is amplified by the > > >> regulator amplifier and pushed out the output port. > > >> > > >> I would experiment by putting a good ceramic 0.1uF cap to ground, right > at > > >> the regulator output port. > > >> > > >> > > >> > > >> > > >> > > >> --- Graham > > >> > > >> > > >> > > >> == > > >> > > >> > > >> > > >> > > >> > > >> On Wed, Dec 7, 2016 at 10:43 AM, Bob Camp <[email protected]> wrote: > > >> > > >> > > >> > > >>> Hi > > >> > > >>> > > >> > > >>> You probably have proven one of the most basic design truths: Parts > > >> > > >>> will > > >> > > >>> *always* oscillate just > > >> > > >>> outside the bandwidth of your test gear” :). A few other possible > issues: > > >> > > >>> > > >> > > >>> 1) Something else is oscillating and it is simply interacting with the > > >> > > >>> regulator in an odd way. > > >> > > >>> 2) The oscillation / noise is at a very low level and it’s below your > > >> > > >>> test gear’s noise floor > > >> > > >>> 3) Testing stops the oscillation > > >> > > >>> > > >> > > >>> Bob > > >> > > >>> > > >> > > >>>> On Dec 6, 2016, at 4:24 PM, Van Horn, David <david.vanhorn@ > > >> > > >>> backcountryaccess.com> wrote: > > >> > > >>>> > > >> > > >>>> Lots of discussion on here about low noise regulation so someone may > > >> > > >>> know what to look for. > > >> > > >>>> > > >> > > >>>> I have a receiver which is getting a lot of interference from > > >> somewhere. > > >> > > >>>> Antenna disconnected, interference still high. > > >> > > >>>> After much poking around, we found that replacing a voltage > > >> > > >>>> regulator > > >> > > >>> with a slightly different part cures the problem. > > >> > > >>>> Running that section on external battery is also fine, so it appears > > >> > > >>>> the > > >> > > >>> original regulator causes some problem. > > >> > > >>>> We tried various batteries over a range of voltages within the chip > > >> > > >>> spec, and couldn't make it have a problem. > > >> > > >>>> > > >> > > >>>> I looked at the reg input and output with scope and spectrum > > >> > > >>>> analyzer, > > >> > > >>> and I don't see anything that indicates excessive noise or oscillation. > > >> > > >>>> The PCB layout is as tight as you could ask for. Fat tracks, lots of > > >> > > >>> ground, I couldn't lay it out any better. > > >> > > >>>> Replacing the input and output caps didn't change anything. > > >> > > >>>> Replacing the input and output caps with parts that should be > > >> > > >>>> "better", > > >> > > >>> like Johanson Tancerams or tantalums has no effect. > > >> > > >>>> > > >> > > >>>> Just for laughs, we tried a number of different regulator chips, all > > >> > > >>>> new > > >> > > >>> from the reel. > > >> > > >>>> The parts with the quietest and with the most noisy specs caused > > >> > > >>> problems. > > >> > > >>>> One part, with a noise spec more or less in the middle of the spread > > >> > > >>>> is > > >> > > >>> the one that works. > > >> > > >>>> > > >> > > >>>> So what is it that a monolithic regulator (linear) can do which is > > >> > > >>>> not > > >> > > >>> observable on a scope or SA, which would cause a receiver to think > > >> > > >>> it's getting a signal or significant noise in band? > > >> > > >>>> Everything else in the system is shut down, I am sure the regulator > > >> > > >>>> chip > > >> > > >>> is the culprit, but so far I don't see how it's causing the problem. > > >> > > >>>> I could just use the quiet chip and move on, but experience tells me > > >> > > >>> that I'd just have problems again down the road. That's voodoo, not > > >> > > >>> science. > > >> > > >>>> > > >> > > >>>> > > >> > > >>>> Ideas? > > >> > > >>>> > > >> > > >>>> > > >> > > >>>> > > >> > > >>>> -- > > >> > > >>>> David VanHorn > > >> > > >>>> Lead Hardware Engineer > > >> > > >>>> > > >> > > >>>> Backcountry Access, Inc. > > >> > > >>>> 2820 Wilderness Pl, Unit H > > >> > > >>>> Boulder, CO 80301 USA > > >> > > >>>> phone: 303-417-1345 x110 > > >> > > >>>> email: [email protected]<mailto:david.vanhorn@ > > >> > > >>> backcountryaccess.com> > > >> > > >>>> > > >> > > >>>> _______________________________________________ > > >> > > >>>> time-nuts mailing list -- [email protected] To unsubscribe, go to > > >> > > >>>> https://www.febo.com/cgi-bin/ > > >> > > >>> mailman/listinfo/time-nuts > > >> > > >>>> and follow the instructions there. > > >> > > >>> > > >> > > >>> _______________________________________________ > > >> > > >>> time-nuts mailing list -- [email protected] To unsubscribe, go to > > >> > > >>> https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow > > >> > > >>> the instructions there. > > >> > > >>> > > >> > > >> _______________________________________________ > > >> > > >> time-nuts mailing list -- [email protected] To unsubscribe, go to > > >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > >> > > >> and follow the instructions there. > > >> > > >> _______________________________________________ > > >> > > >> time-nuts mailing list -- [email protected] > > >> > > >> To unsubscribe, go to > > >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > >> > > >> and follow the instructions there. > > >> > > >> > > > _______________________________________________ > > > time-nuts mailing list -- [email protected] > > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > and follow the instructions there. > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
