On Wed, 22 Dec 2010 20:02:12 -0800 (PST), George Herold <gherold@teachspin.com> wrote:>On Dec 22, 7:45�pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Wed, 22 Dec 2010 14:01:50 -0800 (PST), George Herold >> >> >> >> >> >> <gher...@teachspin.com> wrote: >> >On Dec 21, 6:14 pm, John Larkin >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> OK: LT Spice resistors seem to not have shot noise. >> >> >> John >> >> >Yup, no shot noise in resistors as Kevin says. �(Or perhaps better is >> >to say greatly reduced.) �If you've got some very big resistors in the >> >TIA then it might be possible for the RC corner to be below the 1/f >> >noise corner. �This might sorta look like shot noise.... an extra >> >noise term that is proportional to the current (voltage/R)... but the >> >spectrum of the noise should show it's 1/f and not shot noise. �(Mind >> >you I'm half talking out my arse, I've not tried measuring the noise >> >in big resistors... say 100 Meg and greater) >> >> >George H. >> >> We tested a lot of high-ohm resistors, and the thickfilms do have shot >> noise. But the resistor I'm dealing with now is a liquid, ionic >> conduction, and according to the literature, they have full shot >> noise. >> >> There's something special about metals that smooths out electron flow. >> There's not a lot available online about shot noise in various >> resistor elements, and most of the high-ohm resistor manufacturers >> don't know much about the subject, either. > >Well according to Landauer it's the scattering that 'smooths' out the >electron flow in resistors. Shot noise happens in semiconductors >because it's only those 'few' random electrons (holes) on the far edge >of the thermal distribution that have enough energy to get over the pn >barrier. This random process happens one electron at a time. At >least that's my understanding.I haven't found much stuff, in books or online, about shot noise in non-metallic conductors. Metallic resistors seem to develop shot noise when the dimensions are very small; there are some papers on that. qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf I suppose a thickfilm resistor, with enough nasty boundaries, might not have the long-term coherence to get the smoothing effect. I just don't know. It is sort of academic, from a circuit design standpoint, in the sense that high-value thickfilms are clearly much noisier than metal films and can really trash a TIA.> >How do you distinguish shot noise from 1/f noise in high meg thick >films?By the spectrum, I suppose. It's difficult to measure wideband noise in, say, gohm resistors, because stray capacitance rolls off the measurement system pretty hard. I do have a gadget that might let me see the spectrum of the noise in a 50M resistor with about 10 volts across it, up to a MHz maybe. I'll see if I can try that with various resistor types.> >That's interesting about ionic conduction. Do you have a reference? >I thought, (though I'm often wrong) that liquid ionic conduction >should be similar to that in metals. The only liquid conduction stuff >I've ever done is electroplating copper onto stainless forms. And >there you've got minimal resistance.... Lots of copper sulfate in the >water.I have some references that refer to shot noise in conductivity-based flow cells, essentially "Coulter Counter" type devices. And others that don't. Most annoying. Nanopore devices have a tiny hole in a membrane that separates a fluid chamber, so the resistive area is sort of a very tiny thin disk, so maybe the scattering coherence is minimal. Plus there are ions blundering about, not just electrons. Hey, I'm just the circuit designer. John
noise in LT Spice
Started by ●December 21, 2010
Reply by ●December 23, 20102010-12-23
Reply by ●December 23, 20102010-12-23
John Larkin wrote:> On Wed, 22 Dec 2010 20:02:12 -0800 (PST), George Herold > <gherold@teachspin.com> wrote: > >> On Dec 22, 7:45 pm, John Larkin >> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>> On Wed, 22 Dec 2010 14:01:50 -0800 (PST), George Herold >>> >>> >>> >>> >>> >>> <gher...@teachspin.com> wrote: >>>> On Dec 21, 6:14 pm, John Larkin >>>> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>>>> OK: LT Spice resistors seem to not have shot noise. >>> >>>>> John >>> >>>> Yup, no shot noise in resistors as Kevin says. (Or perhaps better is >>>> to say greatly reduced.) If you've got some very big resistors in the >>>> TIA then it might be possible for the RC corner to be below the 1/f >>>> noise corner. This might sorta look like shot noise.... an extra >>>> noise term that is proportional to the current (voltage/R)... but the >>>> spectrum of the noise should show it's 1/f and not shot noise. (Mind >>>> you I'm half talking out my arse, I've not tried measuring the noise >>>> in big resistors... say 100 Meg and greater) >>> >>>> George H. >>> >>> We tested a lot of high-ohm resistors, and the thickfilms do have shot >>> noise. But the resistor I'm dealing with now is a liquid, ionic >>> conduction, and according to the literature, they have full shot >>> noise. >>> >>> There's something special about metals that smooths out electron flow. >>> There's not a lot available online about shot noise in various >>> resistor elements, and most of the high-ohm resistor manufacturers >>> don't know much about the subject, either. >> >> Well according to Landauer it's the scattering that 'smooths' out the >> electron flow in resistors. Shot noise happens in semiconductors >> because it's only those 'few' random electrons (holes) on the far edge >> of the thermal distribution that have enough energy to get over the pn >> barrier. This random process happens one electron at a time. At >> least that's my understanding. > > I haven't found much stuff, in books or online, about shot noise in > non-metallic conductors. Metallic resistors seem to develop shot noise > when the dimensions are very small; there are some papers on that. > > qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf > > I suppose a thickfilm resistor, with enough nasty boundaries, might > not have the long-term coherence to get the smoothing effect. I just > don't know. It is sort of academic, from a circuit design standpoint, > in the sense that high-value thickfilms are clearly much noisier than > metal films and can really trash a TIA. > >> >> How do you distinguish shot noise from 1/f noise in high meg thick >> films? > > By the spectrum, I suppose. It's difficult to measure wideband noise > in, say, gohm resistors, because stray capacitance rolls off the > measurement system pretty hard. > > I do have a gadget that might let me see the spectrum of the noise in > a 50M resistor with about 10 volts across it, up to a MHz maybe. I'll > see if I can try that with various resistor types. > >> >> That's interesting about ionic conduction. Do you have a reference? >> I thought, (though I'm often wrong) that liquid ionic conduction >> should be similar to that in metals. The only liquid conduction stuff >> I've ever done is electroplating copper onto stainless forms. And >> there you've got minimal resistance.... Lots of copper sulfate in the >> water. > > I have some references that refer to shot noise in conductivity-based > flow cells, essentially "Coulter Counter" type devices. And others > that don't. Most annoying. Nanopore devices have a tiny hole in a > membrane that separates a fluid chamber, so the resistive area is sort > of a very tiny thin disk, so maybe the scattering coherence is > minimal. Plus there are ions blundering about, not just electrons. > Hey, I'm just the circuit designer. > > John > >You can also use its dependence on voltage. For a fixed resistance, shot noise current goes as V**0.5, whereas 1/f current goes as V. 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 ●December 23, 20102010-12-23
"John Larkin" wrote in message news:6g65h65e6o2e45cfqp990tmjtlu8g0cjno@4ax.com... On Wed, 22 Dec 2010 14:01:50 -0800 (PST), George Herold <gherold@teachspin.com>> wrote:>>On Dec 21, 6:14 pm, John Larkin >><jjlar...@highNOTlandTHIStechnologyPART.com>> wrote: >>>> OK: LT Spice resistors seem to not have shot noise. >>>> >>>> John >> >>Yup, no shot noise in resistors as Kevin says. (Or perhaps better is >>to say greatly reduced.) If you've got some very big resistors in the >>TIA then it might be possible for the RC corner to be below the 1/f >>noise corner. This might sorta look like shot noise.... an extra >>noise term that is proportional to the current (voltage/R)... but the >>spectrum of the noise should show it's 1/f and not shot noise. (Mind >>you I'm half talking out my arse, I've not tried measuring the noise >>in big resistors... say 100 Meg and greater) >> >>George H.>We tested a lot of high-ohm resistors, and the thickfilms do have shot >noise. But the resistor I'm dealing with now is a liquid, ionic >conduction, and according to the literature, they have full shot >noise.Do you mean that when there is dc current, there is wideband noise in excess of the thermal noise? This may well be the case, but I still still quibble in naming in it "shot" noise. I would have to have a look at the this literature to see if the actual noise mechanism is the same as that of semiconductor diode and vacuum tube shot noise. Kevin Aylward B.Sc. www.kevinaylward.co.uk
Reply by ●December 23, 20102010-12-23
"John Larkin" wrote in message news:gs55h6tphh6pl8e56a0e7ojp7s271hji4t@4ax.com... On Wed, 22 Dec 2010 21:09:38 -0000, "Kevin Aylward" <seemywebsite@kevinaylward.co.uk>> wrote:>>>>"John Larkin" wrote in message >>>>news:75d2h613cdof17gkfsqpmhqnn9nhkt0vb0@4ax.com... >> >> >>>>OK: LT Spice resistors seem to not have shot noise. >> >>>>John >> >> >>Probably because resistors don't have shot noise! >>>Some do, like high-value thickfilms. Or in my current case, liquid >resistors. Past about 10 megs, it gets harder to buy low-noise metal >film resistors.Unless there is a potential barrier involved, that charges cross, then I don't see it as convential "shot" noise. There may well be other noise with another name, but I don't see that it shot noise because shot noise is, essentially, defined as that noise produced when charges cross a potential barrier. Of course definitions sometimes change.>>However, resistors do have 1/f noise when a dc current is present in them. >>This can be very, very significant in i.c. design. This 1/f noise goes >>with >>1/sqrt(L.W). Poly resistors can be particularly troublesome.>For a flowing liquid, I could imagine lots of low frequency 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. 1/f noise in i.c. resisters are a particular concern of mine, and to date on chips back from fab, I have not seen any evidence of wideband excess noise due to current in poly resisters. I have seen large 1/f noise though. This is particularlly troublesome, when fab vendors models don't model it. Kevin Aylward B.Sc. www.kevinaylward.co.uk
Reply by ●December 23, 20102010-12-23
On Dec 22, 11:57=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Wed, 22 Dec 2010 20:02:12 -0800 (PST), George Herold > > > > > > <gher...@teachspin.com> wrote: > >On Dec 22, 7:45 pm, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Wed, 22 Dec 2010 14:01:50 -0800 (PST), George Herold > > >> <gher...@teachspin.com> wrote: > >> >On Dec 21, 6:14 pm, John Larkin > >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> >> OK: LT Spice resistors seem to not have shot noise. > > >> >> John > > >> >Yup, no shot noise in resistors as Kevin says. (Or perhaps better is > >> >to say greatly reduced.) If you've got some very big resistors in the > >> >TIA then it might be possible for the RC corner to be below the 1/f > >> >noise corner. This might sorta look like shot noise.... an extra > >> >noise term that is proportional to the current (voltage/R)... but the > >> >spectrum of the noise should show it's 1/f and not shot noise. (Mind > >> >you I'm half talking out my arse, I've not tried measuring the noise > >> >in big resistors... say 100 Meg and greater) > > >> >George H. > > >> We tested a lot of high-ohm resistors, and the thickfilms do have shot > >> noise. But the resistor I'm dealing with now is a liquid, ionic > >> conduction, and according to the literature, they have full shot > >> noise. > > >> There's something special about metals that smooths out electron flow. > >> There's not a lot available online about shot noise in various > >> resistor elements, and most of the high-ohm resistor manufacturers > >> don't know much about the subject, either. > > >Well according to Landauer it's the scattering that 'smooths' out the > >electron flow in resistors. =A0Shot noise happens in semiconductors > >because it's only those 'few' random electrons (holes) on the far edge > >of the thermal distribution that have enough energy to get over the pn > >barrier. =A0 This random process happens one electron at a time. =A0At > >least that's my understanding. > > I haven't found much stuff, in books or online, about shot noise in > non-metallic conductors. Metallic resistors seem to develop shot noise > when the dimensions are very small; there are some papers on that. > > qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdfThat makes sense, the shorter it is the fewer scattering events.> > I suppose a thickfilm resistor, with enough nasty boundaries, might > not have the long-term coherence to get the smoothing effect. I just > don't know. It is sort of academic, from a circuit design standpoint, > in the sense that high-value thickfilms are clearly much noisier than > metal films and can really trash a TIA.Yeah it's excess noise, still if it's shot noise it's fundamental and you can't do much about it. If it's 1/f noise, or some other technical thing then there's the chance that a different 'style' of resistor will have less noise. I'm testing a few of our new noise apparatus today. (Max freq is about 1MHz, but only 100kHz if you want any real accuracy.) If I have some time later I could check out the noise in some thick film 100 Megers'. Unfortunately there's several pF of input capacitance and that limit's the frequency response... a lot... gasp less than 1kHz.> > > > >How do you distinguish shot noise from 1/f noise in high meg thick > >films? > > By the spectrum, I suppose. It's difficult to measure wideband noise > in, say, gohm resistors, because stray capacitance rolls off the > measurement system pretty hard. > > I do have a gadget that might let me see the spectrum of the noise in > a 50M resistor with about 10 volts across it, up to a MHz maybe. I'll > see if I can try that with various resistor types. > > > > >That's interesting about ionic conduction. =A0Do you have a reference? > >I thought, (though I'm often wrong) that liquid ionic conduction > >should be similar to that in metals. =A0The only liquid conduction stuff > >I've ever done is electroplating copper onto stainless forms. =A0And > >there you've got minimal resistance.... Lots of copper sulfate in the > >water. > > I have some references that refer to shot noise in conductivity-based > flow cells, essentially "Coulter Counter" type devices. And others > that don't. Most annoying. Nanopore devices have a tiny hole in a > membrane that separates a fluid chamber, so the resistive area is sort > of a very tiny thin disk, so maybe the scattering coherence is > minimal. Plus there are ions blundering about, not just electrons.Interesting. (I never heard of the Coulter Counter.) If there is no scattering as the ion goes through the small hole then this could give shot noise! Even one or two scattering events should still leave some fraction of the shot noise. You can learn something, perhaps, by lookng at the noise, George H.> Hey, I'm just the circuit designer.> > John- Hide quoted text - > > - Show quoted text -
Reply by ●December 23, 20102010-12-23
On Dec 23, 12:58=A0am, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> John Larkin wrote: > > On Wed, 22 Dec 2010 20:02:12 -0800 (PST), George Herold > > <gher...@teachspin.com> =A0wrote: > > >> On Dec 22, 7:45 pm, John Larkin > >> <jjlar...@highNOTlandTHIStechnologyPART.com> =A0wrote: > >>> On Wed, 22 Dec 2010 14:01:50 -0800 (PST), George Herold > > >>> <gher...@teachspin.com> =A0wrote: > >>>> On Dec 21, 6:14 pm, John Larkin > >>>> <jjlar...@highNOTlandTHIStechnologyPART.com> =A0wrote: > >>>>> OK: LT Spice resistors seem to not have shot noise. > > >>>>> John > > >>>> Yup, no shot noise in resistors as Kevin says. =A0(Or perhaps better=is> >>>> to say greatly reduced.) =A0If you've got some very big resistors in=the> >>>> TIA then it might be possible for the RC corner to be below the 1/f > >>>> noise corner. =A0This might sorta look like shot noise.... an extra > >>>> noise term that is proportional to the current (voltage/R)... but th=e> >>>> spectrum of the noise should show it's 1/f and not shot noise. =A0(M=ind> >>>> you I'm half talking out my arse, I've not tried measuring the noise > >>>> in big resistors... say 100 Meg and greater) > > >>>> George H. > > >>> We tested a lot of high-ohm resistors, and the thickfilms do have sho=t> >>> noise. But the resistor I'm dealing with now is a liquid, ionic > >>> conduction, and according to the literature, they have full shot > >>> noise. > > >>> There's something special about metals that smooths out electron flow=.> >>> There's not a lot available online about shot noise in various > >>> resistor elements, and most of the high-ohm resistor manufacturers > >>> don't know much about the subject, either. > > >> Well according to Landauer it's the scattering that 'smooths' out the > >> electron flow in resistors. =A0Shot noise happens in semiconductors > >> because it's only those 'few' random electrons (holes) on the far edge > >> of the thermal distribution that have enough energy to get over the pn > >> barrier. =A0 This random process happens one electron at a time. =A0At > >> least that's my understanding. > > > I haven't found much stuff, in books or online, about shot noise in > > non-metallic conductors. Metallic resistors seem to develop shot noise > > when the dimensions are very small; there are some papers on that. > > > qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf > > > I suppose a thickfilm resistor, with enough nasty boundaries, might > > not have the long-term coherence to get the smoothing effect. I just > > don't know. It is sort of academic, from a circuit design standpoint, > > in the sense that high-value thickfilms are clearly much noisier than > > metal films and can really trash a TIA. > > >> How do you distinguish shot noise from 1/f noise in high meg thick > >> films? > > > By the spectrum, I suppose. It's difficult to measure wideband noise > > in, say, gohm resistors, because stray capacitance rolls off the > > measurement system pretty hard. > > > I do have a gadget that might let me see the spectrum of the noise in > > a 50M resistor with about 10 volts across it, up to a MHz maybe. I'll > > see if I can try that with various resistor types. > > >> That's interesting about ionic conduction. =A0Do you have a reference? > >> I thought, (though I'm often wrong) that liquid ionic conduction > >> should be similar to that in metals. =A0The only liquid conduction stu=ff> >> I've ever done is electroplating copper onto stainless forms. =A0And > >> there you've got minimal resistance.... Lots of copper sulfate in the > >> water. > > > I have some references that refer to shot noise in conductivity-based > > flow cells, essentially "Coulter Counter" type devices. And others > > that don't. Most annoying. Nanopore devices have a tiny hole in a > > membrane that separates a fluid chamber, so the resistive area is sort > > of a very tiny thin disk, so maybe the scattering coherence is > > minimal. Plus there are ions blundering about, not just electrons. > > Hey, I'm just the circuit designer. > > > John > > You can also use its dependence on voltage. =A0For a fixed resistance, > shot noise current goes as V**0.5, whereas 1/f current goes as V. >Duh, 'slaps head', of course. I was thinking they would both be linear in V. George H.> 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) nethttp://electrooptical.ne=t- Hide quoted text -> > - Show quoted text -
Reply by ●December 23, 20102010-12-23
On Dec 23, 7:30=A0am, "Kevin Aylward" <seemywebs...@kevinaylward.co.uk> wrote:> "John Larkin" =A0wrote in message > > news:gs55h6tphh6pl8e56a0e7ojp7s271hji4t@4ax.com... > > On Wed, 22 Dec 2010 21:09:38 -0000, "Kevin Aylward" > > <seemywebs...@kevinaylward.co.uk>> wrote: > >>>>"John Larkin" =A0wrote in message > >>>>news:75d2h613cdof17gkfsqpmhqnn9nhkt0vb0@4ax.com... > > >>>>OK: LT Spice resistors seem to not have shot noise. > > >>>>John > > >>Probably because resistors don't have shot noise! > > >Some do, like high-value thickfilms. Or in my current case, liquid > >resistors. Past about 10 megs, it gets harder to buy low-noise metal > >film resistors. > > Unless there is a potential barrier involved, that charges cross, then I > don't see it as convential "shot" noise. There may well be other noise wi=th> another name, but I don't see that it shot noise because shot noise is, > essentially, defined as that noise produced when charges cross a potentia=l> barrier. Of course definitions sometimes change.You might like the article by Rolf Landauer "Solid State Shot Noise" Phys Rev. B, 47, pg. 16 427 (June '93) I think you can have shot noise in quantum systems without any potential barrier. Say a quantum contact that has a volume only big enough to hold one electron state at a time. (But I'm no expert.) John's ionic system might be similar in some way... if the ionic resistance is determined by a small hole through which only one ion can pass at a time. But I think I agree with you the excess noise in thick film resistors should probably not be called 'shot noise'. George H.> > >>However, resistors do have 1/f noise when a dc current is present in th=em.> >>This can be very, very significant in i.c. design. This 1/f noise goes > >>with > >>1/sqrt(L.W). Poly resistors can be particularly troublesome. > >For a flowing liquid, I could imagine lots of low frequency 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/potenti=al> barrier, so no shot noise. Technically there are the end contacts, but th=ese> are heavily doped to make them ohmic by construction. > > 1/f noise in i.c. resisters are a particular concern of mine, and to date=on> chips back from fab, I have not seen any evidence of wideband excess nois=e> due to current in poly resisters. I have seen large 1/f noise though. Thi=s> is particularlly troublesome, when fab vendors models don't model it. > > Kevin Aylward B.Sc.www.kevinaylward.co.uk
Reply by ●December 23, 20102010-12-23
On Thu, 23 Dec 2010 12:24:37 -0000, "Kevin Aylward" <seemywebsite@kevinaylward.co.uk> wrote:>"John Larkin" wrote in message >news:6g65h65e6o2e45cfqp990tmjtlu8g0cjno@4ax.com... > >On Wed, 22 Dec 2010 14:01:50 -0800 (PST), George Herold ><gherold@teachspin.com>> wrote: > >>>On Dec 21, 6:14 pm, John Larkin >>><jjlar...@highNOTlandTHIStechnologyPART.com>> wrote: >>>>> OK: LT Spice resistors seem to not have shot noise. >>>>> >>>>> John >>> >>>Yup, no shot noise in resistors as Kevin says. (Or perhaps better is >>>to say greatly reduced.) If you've got some very big resistors in the >>>TIA then it might be possible for the RC corner to be below the 1/f >>>noise corner. This might sorta look like shot noise.... an extra >>>noise term that is proportional to the current (voltage/R)... but the >>>spectrum of the noise should show it's 1/f and not shot noise. (Mind >>>you I'm half talking out my arse, I've not tried measuring the noise >>>in big resistors... say 100 Meg and greater) >>> >>>George H. > >>We tested a lot of high-ohm resistors, and the thickfilms do have shot >>noise. But the resistor I'm dealing with now is a liquid, ionic >>conduction, and according to the literature, they have full shot >>noise. > >Do you mean that when there is dc current, there is wideband noise in excess >of the thermal noise? This may well be the case, but I still still quibble >in naming in it "shot" noise. > >I would have to have a look at the this literature to see if the actual >noise mechanism is the same as that of semiconductor diode and vacuum tube >shot noise. > > >Kevin Aylward B.Sc. >www.kevinaylward.co.ukAs I understand it, there are two mechanisms in metals that reduce current noise below the Poissonian statistical value. One is e-e interaction, which is short range and cuts the full-shot noise about in half. The other is electron-phonon interaction, which only works in physically large resistors but smooths the noise almost to zero. http://www.lorentz.leidenuniv.nl/beenakkr/mesoscopics/topics/noise/noise.html I can't find any definitive statement that either works in non-metallic conductors, like cermets maybe. Do phonons get very far in a messy sintered metal oxide thing? What about ionic conductors? What about tiny resistors inside ICs? What about zigzag resistors? Do phonons turn corners? A lot of the good phonon stuff is in papers that cost big bucks. Some retired person could look into this. It's interesting but time consuming. John
Reply by ●December 23, 20102010-12-23
On Thu, 23 Dec 2010 06:21:03 -0800 (PST), George Herold <gherold@teachspin.com> wrote:>On Dec 22, 11:57�pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Wed, 22 Dec 2010 20:02:12 -0800 (PST), George Herold >> >> >> >> >> >> <gher...@teachspin.com> wrote: >> >On Dec 22, 7:45 pm, John Larkin >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> On Wed, 22 Dec 2010 14:01:50 -0800 (PST), George Herold >> >> >> <gher...@teachspin.com> wrote: >> >> >On Dec 21, 6:14 pm, John Larkin >> >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> >> OK: LT Spice resistors seem to not have shot noise. >> >> >> >> John >> >> >> >Yup, no shot noise in resistors as Kevin says. (Or perhaps better is >> >> >to say greatly reduced.) If you've got some very big resistors in the >> >> >TIA then it might be possible for the RC corner to be below the 1/f >> >> >noise corner. This might sorta look like shot noise.... an extra >> >> >noise term that is proportional to the current (voltage/R)... but the >> >> >spectrum of the noise should show it's 1/f and not shot noise. (Mind >> >> >you I'm half talking out my arse, I've not tried measuring the noise >> >> >in big resistors... say 100 Meg and greater) >> >> >> >George H. >> >> >> We tested a lot of high-ohm resistors, and the thickfilms do have shot >> >> noise. But the resistor I'm dealing with now is a liquid, ionic >> >> conduction, and according to the literature, they have full shot >> >> noise. >> >> >> There's something special about metals that smooths out electron flow. >> >> There's not a lot available online about shot noise in various >> >> resistor elements, and most of the high-ohm resistor manufacturers >> >> don't know much about the subject, either. >> >> >Well according to Landauer it's the scattering that 'smooths' out the >> >electron flow in resistors. �Shot noise happens in semiconductors >> >because it's only those 'few' random electrons (holes) on the far edge >> >of the thermal distribution that have enough energy to get over the pn >> >barrier. � This random process happens one electron at a time. �At >> >least that's my understanding. >> >> I haven't found much stuff, in books or online, about shot noise in >> non-metallic conductors. Metallic resistors seem to develop shot noise >> when the dimensions are very small; there are some papers on that. >> >> qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf > >That makes sense, the shorter it is the fewer scattering events. >> >> I suppose a thickfilm resistor, with enough nasty boundaries, might >> not have the long-term coherence to get the smoothing effect. I just >> don't know. It is sort of academic, from a circuit design standpoint, >> in the sense that high-value thickfilms are clearly much noisier than >> metal films and can really trash a TIA. > >Yeah it's excess noise, still if it's shot noise it's fundamental and >you can't do much about it. If it's 1/f noise, or some other >technical thing then there's the chance that a different 'style' of >resistor will have less noise. I'm testing a few of our new noise >apparatus today. (Max freq is about 1MHz, but only 100kHz if you >want any real accuracy.) If I have some time later I could check out >the noise in some thick film 100 Megers'. Unfortunately there's >several pF of input capacitance and that limit's the frequency >response... a lot... gasp less than 1kHz.We had that same problem. 1/f noise could easily mask shot noise, especially if the bandwidth is limited. And higher voltages, as Phil notes, makes the shot signal bigger but the 1/f masking worse. It's always something. The bottom line is that we'll use whatever resistor works best, no matter how you name the noise, but it would sure help to understand this stuff, to better analyze and simulate designs.>> >> >That's interesting about ionic conduction. �Do you have a reference? >> >I thought, (though I'm often wrong) that liquid ionic conduction >> >should be similar to that in metals. �The only liquid conduction stuff >> >I've ever done is electroplating copper onto stainless forms. �And >> >there you've got minimal resistance.... Lots of copper sulfate in the >> >water. >> >> I have some references that refer to shot noise in conductivity-based >> flow cells, essentially "Coulter Counter" type devices. And others >> that don't. Most annoying. Nanopore devices have a tiny hole in a >> membrane that separates a fluid chamber, so the resistive area is sort >> of a very tiny thin disk, so maybe the scattering coherence is >> minimal. Plus there are ions blundering about, not just electrons. > >Interesting. (I never heard of the Coulter Counter.) If there is no >scattering as the ion goes through the small hole then this could give >shot noise! Even one or two scattering events should still leave some >fraction of the shot noise. You can learn something, perhaps, by >lookng at the noise,It's easy, a high school project, to count small particles like bacteria and blood cells with the Coulter technique. There's plenty of signal from things that big! John
Reply by ●December 23, 20102010-12-23
Kevin Aylward wrote:> "John Larkin" wrote in message > news:gs55h6tphh6pl8e56a0e7ojp7s271hji4t@4ax.com... > > On Wed, 22 Dec 2010 21:09:38 -0000, "Kevin Aylward" > <seemywebsite@kevinaylward.co.uk>> wrote: > >>>>> "John Larkin" wrote in message >>>>> news:75d2h613cdof17gkfsqpmhqnn9nhkt0vb0@4ax.com... >>> >>> >>>>> OK: LT Spice resistors seem to not have shot noise. >>> >>>>> John >>> >>> >>> Probably because resistors don't have shot noise! >>> > >> Some do, like high-value thickfilms. Or in my current case, liquid >> resistors. Past about 10 megs, it gets harder to buy low-noise metal >> film resistors. > > > Unless there is a potential barrier involved, that charges cross, then I > don't see it as convential "shot" noise. There may well be other noise > with another name, but I don't see that it shot noise because shot noise > is, essentially, defined as that noise produced when charges cross a > potential barrier. Of course definitions sometimes change. > >>> However, resistors do have 1/f noise when a dc current is present in >>> them. >>> This can be very, very significant in i.c. design. This 1/f noise >>> goes with >>> 1/sqrt(L.W). Poly resistors can be particularly troublesome. > >> For a flowing liquid, I could imagine lots of low frequency 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. > > 1/f noise in i.c. resisters are a particular concern of mine, and to > date on chips back from fab, I have not seen any evidence of wideband > excess noise due to current in poly resisters. I have seen large 1/f > noise though. This is particularlly troublesome, when fab vendors models > don't model it. >This might be of interest here: http://qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
