John Larkin schrieb:> Shot noise is the random arrival of electrons, Poisson statistics. One > amp is one amp, no matter how it's generated. If the electrons are > uncorrelated, you have full shot noise. Metals are remarkable because > physical phenomena correlate the electrons, at least if the conductor > is long enough.Hello, if 1 amp is flowing 1 second long, 6,241,509,629,152,650,000 electrons are passing. It is hard to detect shot noise under this condition, but this is no proof that it does not exist. If we think about 1 nA flowing 1 �s long, we have only 6,241 electrons passing, but it may be 6,242 electrons also. With current less than 1 nA, shot noise is detectable. Bye
noise in LT Spice
Started by ●December 21, 2010
Reply by ●May 6, 20112011-05-06
Reply by ●May 6, 20112011-05-06
Uwe Hercksen wrote:> > > John Larkin schrieb: > >> Shot noise is the random arrival of electrons, Poisson statistics. One >> amp is one amp, no matter how it's generated. If the electrons are >> uncorrelated, you have full shot noise. Metals are remarkable because >> physical phenomena correlate the electrons, at least if the conductor >> is long enough. > > Hello, > > if 1 amp is flowing 1 second long, 6,241,509,629,152,650,000 electrons > are passing. It is hard to detect shot noise under this condition, but > this is no proof that it does not exist. If we think about 1 nA flowing > 1 �s long, we have only 6,241 electrons passing, but it may be 6,242 > electrons also. With current less than 1 nA, shot noise is detectable. > > Bye >The shot noise of a 1A current is trivially detectable, if you have sufficiently advanced gear, such as a sense resistor and a blocking capacitor. The zero-order argument for long resistors having less shot noise is plausible, but its results are wrong in detail, by something like a factor of 3 iirc--it leaves out the fact that the scattering processes that produce the resistance of the rest of the resistor also contribute randomness. Different scattering processes also make the shot noise either better or worse--electron-electron scattering is apparently quite different from scattering from impurity ions or crystal defects, and electron-phonon scattering is different again. Real solid state physics makes my head hurt. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
Reply by ●May 6, 20112011-05-06
On May 5, 11:33=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Thu, 5 May 2011 17:26:58 -0700 (PDT), George Herold > > > > > > <gher...@teachspin.com> wrote: > >On May 5, 4:14=A0pm, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Thu, 05 May 2011 14:33:30 -0500, "George Storm" > > >> <hedley@n_o_s_p_a_m.adaptalog.com> wrote: > >> >>Do resistors have shot noise? > > >> >Resistors don't have shot noise (whatever they may be made of) > > >> >Try the following thought experiment: take a hypothetial resistor wit=h both> >> >shot noise and Johnson noise. =A0The current noise density will be: > >> >In^2 =3D 4.k.T/R + 2.q.I > >> >Now combine four of these resistors in a series-parallel arrangement =to> >> >give a combiner resistance R. > >> >The current noise density of the combination will be: > >> >In^2 =3D 4.k.T/R + q.I > >> >Repeat this N times, and you have: > >> >In^2 =3D 4.k.T/R + 2.q.I/N > > Doesn't make sense to me. If I had a sheet resistor that was one > square, terminals on top and bottom, and was one ohm per square, it > would be one ohm. Imagine 1 volt across it, one amp, and assume the > material has full shot noise. The shot noise is 5.7e-10 amps RMS per > root Hz. > > There's no lateral potential, so I can cut a tiny vertical slit, or > not cut it, and it makes no difference to the resistance or the > current. If I do cut a real or imaginary slit, it becomes four 1-ohm > resistors, each one square, arranged in series-parallel as described > above. The shot noise must be the same since all I did was think about > it. > > Shot noise is the random arrival of electrons, Poisson statistics. One > amp is one amp, no matter how it's generated. If the electrons are > uncorrelated, you have full shot noise. Metals are remarkable because > physical phenomena correlate the electrons, at least if the conductor > is long enough. > > > > > > > > >> >So... =A0even if a miniscule element of the resistor does exhibit sho=t noise,> >> >the resistor as a whole does not. > > >> >>There doesn't seem to be a noise source as a component. > >> >>I could use a resistor Johnson noise, and buffer that > >> >>with a VCVS or VCCS as needed. > > >> > I sometimes do that, but you need to add temperature parameters if y=ou> >> >want the noise to stay constant as you change temperature. =A0It's al=so> >> >inconvenient if you want the noise to relate to a circuit current as =in> >> >shot noise. =A0 > >> > It's rare that I would want to include external shot noise in a circ=uit> >> >simulation, but it could happen (e.g. if you have a sensor that isn't > >> >supported in your version of SPICE). =A0Here is one of many possible =ways to> >> >introduce the shot noise: > >> > =A0You can use an idealised bipolar transistor, drive the circuit cu=rrent> >> >into the base, and set a high current gain (e.g 1000), and drive the > >> >collector output into a (biased) CCCS with the inverse gain (e.g. 1/1=000).> >> >The output current of the CCCS is the same as the circuit current, bu=t with> >> >shot noise (plus a fraction) added. > > >> Photodiodes have shot noise. Liquid (ionic conduction) resistors have > >> shot noise. > > >Have you looked at shot noise in liquids? =A0(You'd need some 'squishy' > >metal box.... > >or a shielded room.) =A0It should go as the scattering length, what's > >the scattering length of ions in liquids? > > Actually, I haven't tried it myself. I have been told that liquids > have full shot noise. I googled it and found nothing definitive.I guess I just have this model in my head that an ionic liquid should look just like a metal resistor, but with slower charge carriers. I could be totally wrong, though. Maybe some sort of screening happens in the liquid? George H.> > John- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -
Reply by ●May 6, 20112011-05-06
On Fri, 06 May 2011 12:59:45 +0200, Uwe Hercksen <hercksen@mew.uni-erlangen.de> wrote:> > >John Larkin schrieb: > >> Shot noise is the random arrival of electrons, Poisson statistics. One >> amp is one amp, no matter how it's generated. If the electrons are >> uncorrelated, you have full shot noise. Metals are remarkable because >> physical phenomena correlate the electrons, at least if the conductor >> is long enough. > >Hello, > >if 1 amp is flowing 1 second long, 6,241,509,629,152,650,000 electrons >are passing. It is hard to detect shot noise under this condition, but >this is no proof that it does not exist.Yup. Full shot noise at 1 amp is 5.66e-10 amps RMS. If we think about 1 nA flowing>1 �s long, we have only 6,241 electrons passing, but it may be 6,242 >electrons also. With current less than 1 nA, shot noise is detectable.It's approaching 0.1% in a KHz bandwidth.> >ByeA photodiode pulse of, say, 100 nA has obvious shot noise as seen on an oscilloscope. We measured a bunch of 50 meg resistors for excess noise. The cermets were very noisy compared to metal films. It's a tricky measurement but not impossible. The spectrum suggested that a lot of the noise was shot noise, but it's hard to keep the bandwidth up at the impedances involved. I conjecture that some very cruddy materials, like cermets and ionic liquids, don't have the long-term ordering that fixes shot noise in metals. There's not much available in the books I have, or online, about shot noise, other than that tubes and semiconductors have it, and metallic resistors don't. John
Reply by ●May 7, 20112011-05-07
"John Larkin"> > There's not much available in the books I have, or online, about shot > noise, other than that tubes and semiconductors have it, and metallic > resistors don't.** Only pure metal resistors are free of excess noise - wire wound and " metal foil " types are two examples. Metal film ( sputtered metal ) resistors are not so blessed having excess noise typically quoted as in the order of 0.1uV/V/decade of frequency - as verified by my tests a couple of years back and posted here. Even Wiki has a neat summary of the basic facts: http://en.wikipedia.org/wiki/Resistor#Electrical_and_thermal_noise .... Phil
Reply by ●May 7, 20112011-05-07
Phil Allison wrote:> "John Larkin" >> >> There's not much available in the books I have, or online, about shot >> noise, other than that tubes and semiconductors have it, and metallic >> resistors don't. > > ** Only pure metal resistors are free of excess noise - wire wound and " > metal foil " types are two examples. > > Metal film ( sputtered metal ) resistors are not so blessed having excess > noise typically quoted as in the order of 0.1uV/V/decade of frequency - as > verified by my tests a couple of years back and posted here. > > Even Wiki has a neat summary of the basic facts: > > http://en.wikipedia.org/wiki/Resistor#Electrical_and_thermal_noise > > > > > .... Phil > > >Excess noise (aka flicker noise and 1/f noise) is a different issue from shot noise. Flicker noise is caused by conductance fluctuations, and is concentrated at low frequency, whereas shot noise is caused by decorrelation of the electrons and is white. (IIRC you pointed that out in one of our recurrent discussions of this topic.) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
Reply by ●May 7, 20112011-05-07
On Sat, 07 May 2011 10:35:16 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Phil Allison wrote: >> "John Larkin" >>> >>> There's not much available in the books I have, or online, about shot >>> noise, other than that tubes and semiconductors have it, and metallic >>> resistors don't. >> >> ** Only pure metal resistors are free of excess noise - wire wound and " >> metal foil " types are two examples. >> >> Metal film ( sputtered metal ) resistors are not so blessed having excess >> noise typically quoted as in the order of 0.1uV/V/decade of frequency - as >> verified by my tests a couple of years back and posted here. >> >> Even Wiki has a neat summary of the basic facts: >> >> http://en.wikipedia.org/wiki/Resistor#Electrical_and_thermal_noise >> >> >> >> >> .... Phil >> >> >> > >Excess noise (aka flicker noise and 1/f noise) is a different issue from >shot noise. Flicker noise is caused by conductance fluctuations, and is >concentrated at low frequency, whereas shot noise is caused by >decorrelation of the electrons and is white. > >(IIRC you pointed that out in one of our recurrent discussions of this >topic.) > >Cheers > >Phil HobbsYou forgot to describe one over f.
Reply by ●May 7, 20112011-05-07
On Sat, 7 May 2011 23:22:37 +1000, "Phil Allison" <phil_a@tpg.com.au> wrote:> >"John Larkin" >> >> There's not much available in the books I have, or online, about shot >> noise, other than that tubes and semiconductors have it, and metallic >> resistors don't. > >** Only pure metal resistors are free of excess noise - wire wound and " >metal foil " types are two examples. > >Metal film ( sputtered metal ) resistors are not so blessed having excess >noise typically quoted as in the order of 0.1uV/V/decade of frequency - as >verified by my tests a couple of years back and posted here. > >Even Wiki has a neat summary of the basic facts: > >http://en.wikipedia.org/wiki/Resistor#Electrical_and_thermal_noise > > > > >.... Phil > >I still haven't found a reference that says whether nonmetallic resistors and ionic liquids have true (uncorrelated electron) shot noise. Shot and 1/f and whatever are usually lumped as "excess noise." Electrons do like to spread out evenly. Even a vacuum diode has somewhat less than shot noise because of mutual electron repulsion. We needed a 50M low-noise resistor, to make a small bias current in about a 2 MHz system, and cermets were terible. We used two 25M Dale axials in series, RN55 types, probably vacuum coated films on ceramic tubes, and they appered to have no excess noise. The rest of the board was all surface mount, so we flew them over other parts, with a mid-air solder joint. It would be an interesting project to measure various resistors for shot noise. I wish I had the time. John
Reply by ●May 7, 20112011-05-07
On Thursday, December 23, 2010 4:30:26 AM UTC-8, Kevin Aylward wrote:> "John Larkin" wrote \ > >>>>OK: LT Spice resistors seem to not have shot noise.> >Do poly resistors have shot noise? Semiconductor currents generally > >have full shot noise. > > Poly resisters are continuous sheet of poly. There is no junction/potential > barrier, so no shot noise. Technically there are the end contacts, but these > are heavily doped to make them ohmic by construction.But, isn't there recombination noise? The charge carriers can enter and leave the channel by recombination, just as by injection, and that DOES carry some shot noise. It'd depend on the geometry of the resistor, and the (?Debye) distance scale.
Reply by ●May 7, 20112011-05-07
On Sat, 7 May 2011 10:53:58 -0700 (PDT), whit3rd <whit3rd@gmail.com> wrote:>On Thursday, December 23, 2010 4:30:26 AM UTC-8, Kevin Aylward wrote: >> "John Larkin" wrote \ >> >>>>OK: LT Spice resistors seem to not have shot noise. > >> >Do poly resistors have shot noise? Semiconductor currents generally >> >have full shot noise. >> >> Poly resisters are continuous sheet of poly. There is no junction/potential >> barrier, so no shot noise. Technically there are the end contacts, but these >> are heavily doped to make them ohmic by construction.Suppose a conventional resistor (metal plates with highly resistive element between) were squashed very thin and flat, so that electrons crossing between plates were far away from others laterally, and crossed quickly enough that they had little likelyhood of interacting with nearby ones. Wouldn't that result in shot noise? Geometrically, that would be like a semiconductor junction, large area but very thin, so electrons cross but don't get much opportunity to correlate.> >But, isn't there recombination noise? The charge carriers can enter >and leave the channel by recombination, just as by injection, >and that DOES carry some shot noise. It'd depend on the >geometry of the resistor, and the (?Debye) distance scale.I found this: http://www.math.tamu.edu/~berko/banff/talk-slides/banff08-macucci.pdf It says that mechanisms like geometry and scattering impurities can break up electron ordering and result in values around 1/3 full shot noise. Some geometries have Fano factors closer to 1. As a practical matter, probably any resistor cruddy enough to have shot noise would have unacceptable amounts of 1/f noise. John
