On May 26, 8:27=A0pm, Mike <s...@me.not> wrote:> dagmargoodb...@yahoo.com wrote: > > I was thinking about that. =A0Maxwell Technology makes unit with > > milliohm ESRs, but I wasn't sure there wasn't some funky > > noise problem, like electrolyte convection or who knows what. > > > Oh, and they're a few cubic inches--not surface mountable. > > > But as for leakage, I've seen a *really* clever dodge around that. > > Walt Jung, I think, in a low-noise reference IIRC. > > > =A0 Here's Walt's article: > > =A0http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdfThat'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
C-multiplier again
Started by ●May 22, 2010
Reply by ●May 26, 20102010-05-26
Reply by ●May 27, 20102010-05-27
On May 26, 8:28=A0pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> dagmargoodb...@yahoo.com wrote: > > On May 24, 3:57 pm, David Eather <eat...@tpg.com.au> wrote: > >> On 24/05/2010 12:11 PM, dagmargoodb...@yahoo.com wrote: > > >>> On May 23, 6:56 pm, David Eather<eat...@tpg.com.au> =A0wrote:> >>> If by 46dB you mean power, i.e. 20log(Vin/Vout) =3D 46, yes, that's > >>> easily possible--that implies 0.5% gain accuracy. > >>> > >>> If you mean 46dBv, i.e. 10log(Vin/Vout) =3D 46, i.e. Vout / Vin =3D 2=5ppm,> >>> no, that ain't happening, not unless you use op amps and some mighty > >>> fine resistors. > >> > >> Um, I thought power was 10*log(what ever / what ever else) and voltage > >> was 20*log(what ever / what ever else) e.g. a reduction in ripple of 4=6> >> db =3D a factor of 200, no? > > > My description was crap--it was a question of notation. =A0I'm not sure > > of the dB convention as applied to these circuit--some R.F. work a > > ways back ruined me. > > > In R.F., 'dB' in our shop meant a ratio of powers unless otherwise > > specified. =A0So, if you said '40dB' I'd assume you meant a ratio of > > 10,000 in power, or, equivalently--power being V^2/R--that you meant a > > factor of merely 100, voltage. > > > I vaguely recall, but I don't remember clearly, that we used to used > > the symbol 'dBv' to designate when a ratio of voltages was being > > reported. =A0To convert that to power comparison, we'd have to multiply > > those dB by 2. > > > Anyway, the other posts have cleared it all up. =A0Thanks. > > > Decibels are always a power ratio. =A0That formula with a 20 in it is a > convenience for when you're measuring everything at the same impedance > level, or when impedance isn't particularly relevant, e.g. at an op amp > output.Thanks, that's clear, but it does seem sort of a lame way to spec op- amps, where impedance is ill-defined, nearly infinite, or otherwise mysterious. Voltage is what we all care about. John's right about dBV being absolute, as dBmV were also--that's what was haunting the dim cobwebs of ye olde noggin. We made and mixed measurements in dB, dBm, dBV, dBmV, etc., all to quantify the same things (i.e. to measure gain, noise, and power). Converting mixed measurements was annoying. -- Cheers, James Arthur
Reply by ●May 27, 20102010-05-27
dagmargoodboat@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 ArthurYes, 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
Reply by ●May 27, 20102010-05-27
On a sunny day (Wed, 26 May 2010 19:23:49 -0700) it happened John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in <iilrv5l0t83k7mkmv4hdbr0105hd5o0974@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).
Reply by ●May 27, 20102010-05-27
On May 26, 7:23=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Wed, 26 May 2010 18:06:20 -0700 (PDT), MooseFET > > > > <kensm...@rahul.net> wrote: > >On May 26, 7:02=A0am, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Wed, 26 May 2010 06:56:18 -0700 (PDT), dagmargoodb...@yahoo.com > >> wrote: > > >> >On May 26, 8:26=A0am, Winfield Hill =A0<Winfield_mem...@newsguy.com> > >> >wrote: > >> >> John Larkin wrote... > > >> ><snip> > > >> >> > How about an opamp powered from Vout, with a resistor from the op=amp> >> >> > 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) > > >> >> =A0+15V >--+--------+--/\/\--+-----> Vout 14.8v > >> >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A04.7R =A0| > >> >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 R3 =A0 =A0 =A0 =A0| > >> >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A02.7M =A0 =A0 =A0 | > >> >> =A0 =A0 =A0 =A0 =A0} =A0 =A0 =A0 =A0| =A0 =A0 =A0 _| > >> >> =A0 =A0 =A0 =A0 =A0| =A0 C1 =A0 +------| =A0\ =A0 =A0 =A0 > >> >> =A0 =A0 =A0 =A0 =A0'---||---+ =A0 =A0 =A0| =A0 >--+---, > >> >> =A0 =A0 =A0 =A0 =A0 =A0 10uF =A0| =A0 ,--|__/ =A0 | =A0 | > >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 | =A0 =A0| =A0 =A0| =A0 | > >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0R7 =A0 '--- |----' =A0R4 > >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0TBD 27k =A0 =A0 | =A0 =A0 =A0 4.7R > >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 ==A0|> >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 --+--------+--------+---- > > >> >> =A0I see your idea, not bad. =A0It's a nice simplification of this, > >> >> =A0incorporating the current-sinking transistor into the opamp. > > >> >> =A0+15V >--+--------+--------+----/\/\--+-----> Vout 14.8v > >> >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A04.7R ==A0|> >> >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 R3 =A0 =A0 =A0 =A0| =A0 =A0 =A0 ==A0 =A0|> >> >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A02.7M =A0 =A0 =A0 | =A0 =A0 =A0 =A0 ==A0|> >> >> =A0 =A0 =A0 =A0 =A0} =A0 =A0 =A0 =A0| =A0 =A0 =A0 _| =A0 =A0 =A0 ==A0 =A0|> >> >> =A0 =A0 =A0 =A0 =A0| =A0 C1 =A0 +------| =A0\ =A0 =A0 =A0 |/ > >> >> =A0 =A0 =A0 =A0 =A0'---||---+ =A0 =A0 =A0| =A0 >------| > >> >> =A0 =A0 =A0 =A0 =A0 =A0 10uF =A0| =A0 ,--|__/ =A0 =A0 =A0 |\V > >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 | =A0 =A0| =A0 =A0 =A0 ==A0 =A0|> >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0R7 =A0 '--- |----------+ > >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 TBD =A0 =A0 =A0 =A0| =A0 =A0 =A0 ==A0 =A0|> >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A027k =A0 =A0 =A0 | =A0 =A0 =A0 ==A0 R4> >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 ==A0 4.7R> >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 ==A0 =A0|> >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 --+--------+----------+---- > > >> >> =A0This scheme is DC regulating as well. =A0The class-A current > >> >> =A0is set by R3 and R7, so the dc voltage drop is fixed. > > >> >Both give line regulation, true. =A0John's problem seems to be that h=e> >> >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. =A0If the ultra-clean part of the load is separable, I'd do th=at.> > >> >If John really needs low-dropout, 15mA, tight load regulation, and lo=w> >> >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 linke=d> >> >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? =A0(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. =A0How 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
Reply by ●May 27, 20102010-05-27
On May 27, 3:02=A0am, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote:> On a sunny day (Wed, 26 May 2010 19:23:49 -0700) it happened John Larkin > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote in > <iilrv5l0t83k7mkmv4hdbr0105hd5o0...@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 :-) > =A0http://panteltje.com/panteltje/mvp/mpv-0.2-pcb.jpg > > Here used as power indicator, and 1.5V reference (old LED).You don't want light hitting your "low noise reference diode" I suggested a blue LED under the assumption that the higher forward voltage would make the "SNR" better by making the "signal" bigger. Since then, I have had a reason to rethink that. I think that the impedance of the so called "super bright" RED is lower than that of the BLUE. BTW: There is no such thing as a superbright LED. LEDs come in 3 brightness classes: (1) Are you sure this is on (2) Way to dim (3) I guess this will do I use LEDs in full sunlight.
Reply by ●May 27, 20102010-05-27
On May 26, 6:27=A0pm, Mike <s...@me.not> wrote: [....]> =A0http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdfI have a slightly improved version: !\U1 Ref ------[R]--+------------! >-----+- Low noise version ! !/ ! ! ! C1[C] ---[R]---+---[R]-+ ! ! ! ! ! ! /-!-- [R] ---+--< ! ! \+!----------+ U2 ! [C]C2 ! GND The time constant at C2 can be huge because the leakage of C2 doesn't cause your reference to be low. The gain of U2 makes C1 look larger than it is. The circuit is second order so it does have a noise peak at the corner but that can be at a very low frequency. The resistors on U2 are low value ones because they add directly to the noise.
Reply by ●May 27, 20102010-05-27
On a sunny day (Thu, 27 May 2010 06:19:51 -0700 (PDT)) it happened MooseFET <kensmith@rahul.net> wrote in <1c06ced9-19ad-466f-9d89-788a725e939f@u3g2000prl.googlegroups.com>:>> �http://panteltje.com/panteltje/mvp/mpv-0.2-pcb.jpg >> >> Here used as power indicator, and 1.5V reference (old LED). > >You don't want light hitting your "low noise reference diode"That is true.>I suggested a blue LED under the assumption that the higher >forward voltage would make the "SNR" better by making the >"signal" bigger. Since then, I have had a reason to rethink >that. I think that the impedance of the so called "super >bright" RED is lower than that of the BLUE.I have never measured that, next time I will have a look with the LEDs I have.>BTW: There is no such thing as a superbright LED. LEDs come >in 3 brightness classes: >(1) Are you sure this is on >(2) Way to dim >(3) I guess this will doI think there is a fourth class, AAAAUAUWW --- Way too bright. Those are the one I have, even at 10 mA, green, and blue, no way can you look into one.>I use LEDs in full sunlight.I try to use clear plastic LEDs, so if you see color it means it is 'on'. Ultimately you can flash a LED to make it stick out a bit more if it is an important indicator. After that transflective LCDs, with flashing background and beep, I have some very small 5 V beepers that almost make you jump :-)
Reply by ●May 27, 20102010-05-27
MooseFET <kensmith@rahul.net> wrote:> On May 26, 6:27�pm, Mike <s...@me.not> wrote: > [....] >> �http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdf > > I have a slightly improved version: > > !\U1 > Ref ------[R]--+------------! >-----+- Low noise version > ! !/ ! > ! ! > C1[C] ---[R]---+---[R]-+ > ! ! ! ! > ! ! /-!-- [R] > ---+--< ! ! > \+!----------+ > U2 ! > [C]C2 > ! > GND > > The time constant at C2 can be huge because the leakage of C2 > doesn't cause your reference to be low. > > The gain of U2 makes C1 look larger than it is. The circuit > is second order so it does have a noise peak at the corner > but that can be at a very low frequency. The resistors on > U2 are low value ones because they add directly to the noise.I'm having trouble figuring the values. Can you post that in LTspice? Mike
Reply by ●May 27, 20102010-05-27
On May 26, 4:53=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Wed, 26 May 2010 13:03:33 -0700 (PDT), dagmargoodb...@yahoo.com > wrote: > > > > > > >On May 26, 10:57 am, Mike <s...@me.not> wrote: > >> Winfield Hill <Winfield_mem...@newsguy.com> wrote: > > >> [...] > > >> > 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. > > >> Cancellation schemes give a 6dB/octave drop to a notch frequency, then=a> >> 6dB/octave rise. The depth of the notch is extremely sensitive to the > >> emitter resistance and probably the temperature of the transistor. Som=e> >> examples may show large amounts of second harmonic distortion on the > >> output. This does not appear on the frequency analysis plot. > > >> In this example, the notch frequency is about 2KHz with a depth of -92=dB.> >> Try changing the emitter resistance to get an idea of how critical it =is.> > >> I don't think you want to rely on this method for any more than a mino=r> >> amount of cancellation, say 20 dB or thereabouts. > > >> Mike > > ><snip LTSpice model> > > >20dB sounds about right. =A0The advantages of this approach are low drop=-> >out voltage and superior low-frequency noise cancellation (compared to > >practical passive equivalents). > > >A big part of the dynamic limitation is the f.f. network rolling off. > >If you change C1 to 100uF, and tack 100uF on the output to cover the > >high-end, overall performance is much improved--nearly as good as a > >passive version using 10,000uF caps, and a lot smaller. > > >For super massive attenuation of input noise and ripple, other > >approaches are better. > > >If John could knock down that 50mV switcher ripple with an LC at the > >input, that's a bonus. =A0But he won't--The Brat would kill him. > > No, I survived. The Gerbered board had... > > Wall wart connector > > Polyfuse > > Transzorb > > 10 uF ceramic > > 47 uH inductor > > two 10 uF ceramics and one 120 uF polymer aluminum to make "+15 > volts." That's 12 dB/octave starting at about 2 KHz. > > Then the LM8261 low-noise LDO reg, which has its own 15 ohms + 2x10uF > + 120uF at its output. > > I also use two Hobbsonian c-multipliers in other supplies that don't > need LDO or regulation. > > Paranoia, groveling for nanovolts. > > But I really need to measure some actual c-multiplier circuits to see > what the Early slopes are like. Could be that LT Spice is grossly > pessimistic. I note here that everyone, including myself, would rather > sit in a swivel chair and simulate and theorize, than get up and > solder and measure.OK this is still a sim. However I spiced the C-multiplier (aka Hobbs filter at teachspin) I use to get down to ~1nV. I haven't every bumped into the Early effect (I don't do much on the transistor level.) But this shows attenuation down near 90dB at 100kHz. (Which is where the switcher I use lives.) George H. Version 4 SHEET 1 1140 1108 WIRE -608 -448 -688 -448 WIRE -448 -448 -528 -448 WIRE 80 -448 -448 -448 WIRE 112 -448 80 -448 WIRE -448 -432 -448 -448 WIRE 112 -400 112 -448 WIRE -448 -352 -512 -352 WIRE -400 -352 -448 -352 WIRE -304 -352 -320 -352 WIRE -224 -352 -304 -352 WIRE -112 -352 -224 -352 WIRE 48 -352 -32 -352 WIRE -688 -320 -688 -448 WIRE -512 -320 -512 -352 WIRE -224 -304 -224 -352 WIRE -448 -288 -448 -352 WIRE -304 -288 -304 -352 WIRE 112 -288 112 -304 WIRE 208 -288 112 -288 WIRE 256 -288 208 -288 WIRE 112 -256 112 -288 WIRE 208 -256 208 -288 WIRE -688 -224 -688 -240 WIRE -512 -224 -512 -256 WIRE -448 -224 -512 -224 WIRE -304 -224 -448 -224 WIRE -224 -224 -224 -240 WIRE -224 -224 -304 -224 WIRE -448 -208 -448 -224 WIRE 208 -176 208 -192 WIRE 208 -176 112 -176 WIRE 112 -160 112 -176 FLAG -448 -208 0 FLAG -688 -224 0 FLAG 112 -160 0 FLAG 80 -448 Vin FLAG 208 -288 Vout SYMBOL npn 48 -400 R0 SYMATTR InstName Q1 SYMATTR Value 2N4401 SYMBOL voltage -688 -336 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 15 SYMBOL voltage -512 -448 R90 WINDOW 0 49 39 VRight 0 WINDOW 123 -48 40 VRight 0 WINDOW 39 0 0 Left 0 Oh, and thanks again Mike for showing me how to post and read the LTspice stuff... I feel so empowered.> > John- Hide quoted text - > > - Show quoted text -
