C-multiplier again
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From: John Larkin on 26 May 2010 23:31 On Thu, 27 May 2010 03:12:25 GMT, Mike <spam(a)me.not> wrote: >dagmargoodboat(a)yahoo.com wrote: >>> � Here's Walt's article: >>> >>> �http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdf >> >> That's it! Thanks. I found in on my computer in a weird scan format, >> and was starting to ASCII it for the group... >> >> Don't you love that bootstrap for the electrolytics? That's slick. >> >> One thing I bet Walt didn't have--50mV of switcher ripple. >> >> -- >> Cheers, >> James Arthur > >Yes, I thought it was pretty neat. As far as switcher ripple, the article >was written in 1993. The PC had been out for about a decade, and the >switching noise was probably a lot worse than it is now. > >Mike > R3, with nearly a nV/rthz added noise, is unfortunate. John
From: Mike on 27 May 2010 02:09 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > On Thu, 27 May 2010 03:12:25 GMT, Mike <spam(a)me.not> wrote: >>>> � Here's Walt's article: >>>> >>>> �http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pd > R3, with nearly a nV/rthz added noise, is unfortunate. > John 49.9 ohms? 0.906nVrms? Is that the one you mean? It's not clear why it's even in the circuit. I think we can simply use R1, R2 and C1, C2, and forget the rest. Mike
From: Jan Panteltje on 27 May 2010 06:02 On a sunny day (Wed, 26 May 2010 19:23:49 -0700) it happened John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in <iilrv5l0t83k7mkmv4hdbr0105hd5o0974(a)4ax.com>: >I could have used an LED, which would be cool - >they light up! - but I didn't want any stray light inside our box. Stick it outside then :-) http://panteltje.com/panteltje/mvp/mpv-0.2-pcb.jpg Here used as power indicator, and 1.5V reference (old LED).
From: dagmargoodboat on 27 May 2010 08:06 On May 26, 11:31 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Thu, 27 May 2010 03:12:25 GMT, Mike <s...(a)me.not> wrote: > >dagmargoodb...(a)yahoo.com wrote: > >>> Here's Walt's article: > > >>> http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdf > > >> That's it! Thanks. I found in on my computer in a weird scan format, > >> and was starting to ASCII it for the group... > > >> Don't you love that bootstrap for the electrolytics? That's slick. > > >> One thing I bet Walt didn't have--50mV of switcher ripple. > > >> -- > >> Cheers, > >> James Arthur > > >Yes, I thought it was pretty neat. As far as switcher ripple, the article > >was written in 1993. The PC had been out for about a decade, and the > >switching noise was probably a lot worse than it is now. > > >Mike > > R3, with nearly a nV/rthz added noise, is unfortunate. > > John Necessary, to protect the AD797 input. James
From: MooseFET on 27 May 2010 09:14
On May 26, 7:23 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Wed, 26 May 2010 18:06:20 -0700 (PDT), MooseFET > > > > <kensm...(a)rahul.net> wrote: > >On May 26, 7:02 am, John Larkin > ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> On Wed, 26 May 2010 06:56:18 -0700 (PDT), dagmargoodb...(a)yahoo.com > >> wrote: > > >> >On May 26, 8:26 am, Winfield Hill <Winfield_mem...(a)newsguy.com> > >> >wrote: > >> >> John Larkin wrote... > > >> ><snip> > > >> >> > How about an opamp powered from Vout, with a resistor from the opamp > >> >> > output to ground? Let the opamp supply current fight the output > >> >> > ripple. That's thermally stable, simple, high gain, and tunable. > > >> >> > (except I need regulation, too) > > >> >> +15V >--+--------+--/\/\--+-----> Vout 14.8v > >> >> | | 4.7R | > >> >> | R3 | > >> >> | 2.7M | > >> >> } | _| > >> >> | C1 +------| \ > >> >> '---||---+ | >--+---, > >> >> 10uF | ,--|__/ | | > >> >> | | | | | > >> >> R7 '--- |----' R4 > >> >> TBD 27k | 4.7R > >> >> | | | > >> >> --+--------+--------+---- > > >> >> I see your idea, not bad. It's a nice simplification of this, > >> >> incorporating the current-sinking transistor into the opamp. > > >> >> +15V >--+--------+--------+----/\/\--+-----> Vout 14.8v > >> >> | | | 4.7R | > >> >> | R3 | | > >> >> | 2.7M | | > >> >> } | _| | > >> >> | C1 +------| \ |/ > >> >> '---||---+ | >------| > >> >> 10uF | ,--|__/ |\V > >> >> | | | | > >> >> R7 '--- |----------+ > >> >> TBD | | > >> >> 27k | R4 > >> >> | | 4.7R > >> >> | | | > >> >> --+--------+----------+---- > > >> >> This scheme is DC regulating as well. The class-A current > >> >> is set by R3 and R7, so the dc voltage drop is fixed. > > >> >Both give line regulation, true. John's problem seems to be that he > >> >needs(?) load regulation too. > > >> If there's no voltage reference, there's no regulation. > > >> >The multi-pole BJT C-mult looks great for feather-weight and constant > >> >loads. If the ultra-clean part of the load is separable, I'd do that. > > >> >If John really needs low-dropout, 15mA, tight load regulation, and low > >> >noise, my best shot so far is to bootstrap the op-amp's supplies on > >> >the Gerber'd "filtered-reference feeding a R-R op-amp" thing he linked > >> >to, to circumvent the op amp's CMRR / PSRR feeding thru. > > >> >Or, I guess, feed the op amp with a steady voltage, e.g., to make an > >> >ultra-clean supply, start with an ultra-clean supply... > > >> >Or cascade a couple such op-amp stages, each feeding the next, each > >> >stage improving PSRR by whatever it can muster. 50-60dB? (I don't > >> >really trust op amps to have low noise and amazing PSRRs and CMRRs > >> >over frequency, but then I've not looked at all the latest and > >> >greatest.) > > >> All I want is a SOT-23 LDO regulator with 1 nv/rthz noise, 140 dB PSRR > >> to 1 MHz, and not made by Maxim. > > >I have an interesting idea. How about a blue LED as the reference. > >It > >is a forward biased diode so it may be low noise. > > >> John > > That sounds familiar. Its dynamic impedance (hence Johnson noise) is > low. I recently did the math to compare shot noise (which a diode has) > to the Johnson noise. If I did it right, the shot noise current dumped > into the dynamic impedance is somewhat less than the Johnson noise, so > the sum isn't a lot higher than the Johnson noise alone. > > I just used two diodes in series to make a low-noise -1.5 volt > shunt-type supply. I could have used an LED, which would be cool - > they light up! - but I didn't want any stray light inside our box. I have used the lighting of the LED to make my "I'm maxed out" indicator out of the very same part that did the limiting. In a low noise application, you don't want light hitting the LED that does the limiting (at least with a red one) because the LED is photovoltaic. > > John |