John Larkin wrote:> 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. > > 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. >Actually, there is: http://qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf http://www.lorentz.leidenuniv.nl/beenakkr/mesoscopics/topics/noise/noise.html [...] -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
noise in LT Spice
Started by ●December 21, 2010
Reply by ●December 23, 20102010-12-23
Reply by ●December 23, 20102010-12-23
On Thu, 23 Dec 2010 15:41:49 -0800, Joerg <invalid@invalid.invalid> wrote:>John Larkin wrote: >> 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. >> >> 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. >> > >Actually, there is: > >http://qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf >http://www.lorentz.leidenuniv.nl/beenakkr/mesoscopics/topics/noise/noise.html >Well, that's just about metallic conductors. Nobody much talks about other stuff. But 0.1 mm isn't all that small a distance. Resistors inside ICs can be smaller than that. John
Reply by ●December 23, 20102010-12-23
On Dec 23, 6:33=A0pm, Joerg <inva...@invalid.invalid> wrote:> Kevin Aylward 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 > > with another name, but I don't see that it shot noise because shot nois=e> > 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 model=s> > 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.- Hide quoted text - > > - Show quoted text -That's great, Thanks Joerg. John's link was to the theory by Beenakker. George H.
Reply by ●December 23, 20102010-12-23
On Dec 23, 8:48=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Thu, 23 Dec 2010 15:41:49 -0800, Joerg <inva...@invalid.invalid> > wrote: > > > > > > >John Larkin 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. =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 the > >>> spectrum of the noise should show it's 1/f and not shot noise. =A0(Mi=nd> >>> 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. > > >Actually, there is: > > >http://qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf > >http://www.lorentz.leidenuniv.nl/beenakkr/mesoscopics/topics/noise/no... > > Well, that's just about metallic conductors. Nobody much talks about > other stuff. > > But 0.1 mm isn't all that small a distance. Resistors inside ICs can > be smaller than that. > > John- Hide quoted text - > > - Show quoted text -Yeah, but what's important (as I read it) is the ratio of scattering length to resistor length. It's not easy to see the shot noise signals in normal resistors. I tried to measure excess noise in 100 meg resistors at the end of the day today. I failed. It might be a circuit mistake. I had a low noise power supply feeding a 100meg thick film with the other end into a TIA opamp. (Fet, opa134). The feed back resistor was another 100meg resistor. The circuit had an RC corner at about 600Hz. I set the output time constant at 1 second. This gave me a pretty noisy noise signal. (I didn't want to wait around for a longer TC. I was the only one left 'at work' 5PM before the holiday.) So I was only sensitive to excess noise at say the 10% -20% of thermal noise level. I changed the voltage from zero to 100mV to 1 volt and 8 volts. And saw no increase in the noise. When I disconected the input resistor the noise dropped by 1/2. I should try the same circiut with some carbon composite resistors! Do they make those at 100 meg? George H.
Reply by ●December 24, 20102010-12-24
On Thu, 23 Dec 2010 19:16:42 -0800 (PST), George Herold <gherold@teachspin.com> wrote:>On Dec 23, 8:48�pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Thu, 23 Dec 2010 15:41:49 -0800, Joerg <inva...@invalid.invalid> >> wrote: >> >> >> >> >> >> >John Larkin 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. >> >> >Actually, there is: >> >> >http://qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf >> >http://www.lorentz.leidenuniv.nl/beenakkr/mesoscopics/topics/noise/no... >> >> Well, that's just about metallic conductors. Nobody much talks about >> other stuff. >> >> But 0.1 mm isn't all that small a distance. Resistors inside ICs can >> be smaller than that. >> >> John- Hide quoted text - >> >> - Show quoted text - > >Yeah, but what's important (as I read it) is the ratio of scattering >length to resistor length. It's not easy to see the shot noise >signals in normal resistors. > >I tried to measure excess noise in 100 meg resistors at the end of the >day today. I failed. It might be a circuit mistake. I had a low >noise power supply feeding a 100meg thick film with the other end into >a TIA opamp. (Fet, opa134). The feed back resistor was another 100meg >resistor. The circuit had an RC corner at about 600Hz. I set the >output time constant at 1 second.I don't understand that part, the 1 second time constant. John This gave me a pretty noisy noise>signal. (I didn't want to wait around for a longer TC. I was the >only one left 'at work' 5PM before the holiday.) So I was only >sensitive to excess noise at say the 10% -20% of thermal noise level. >I changed the voltage from zero to 100mV to 1 volt and 8 volts. And >saw no increase in the noise. When I disconected the input resistor >the noise dropped by 1/2. I should try the same circiut with some >carbon composite resistors! Do they make those at 100 meg? > >George H.
Reply by ●December 24, 20102010-12-24
On Dec 23, 11:50=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Thu, 23 Dec 2010 19:16:42 -0800 (PST), George Herold > > > > > > <gher...@teachspin.com> wrote: > >On Dec 23, 8:48 pm, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Thu, 23 Dec 2010 15:41:49 -0800, Joerg <inva...@invalid.invalid> > >> wrote: > > >> >John Larkin 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. (Mi=nd> >> >>> you I'm half talking out my arse, I've not tried measuring the noi=se> >> >>> in big resistors... say 100 Meg and greater) > > >> >>> George H. > > >> >> We tested a lot of high-ohm resistors, and the thickfilms do have s=hot> >> >> 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 fl=ow.> >> >> 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. > > >> >Actually, there is: > > >> >http://qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf > >> >http://www.lorentz.leidenuniv.nl/beenakkr/mesoscopics/topics/noise/no=...> > >> Well, that's just about metallic conductors. Nobody much talks about > >> other stuff. > > >> But 0.1 mm isn't all that small a distance. Resistors inside ICs can > >> be smaller than that. > > >> John- Hide quoted text - > > >> - Show quoted text - > > >Yeah, but what's important (as I read it) is the ratio of scattering > >length to resistor length. =A0It's not easy to see the shot noise > >signals in normal resistors. > > >I tried to measure excess noise in 100 meg resistors at the end of the > >day today. =A0I failed. =A0It might be a circuit mistake. =A0 I had a lo=w> >noise power supply feeding a 100meg thick film with the other end into > >a TIA opamp. (Fet, opa134). =A0The feed back resistor was another 100meg > >resistor. =A0The circuit had an RC corner at about 600Hz. =A0I set the > >output time constant at 1 second. > > I don't understand that part, the 1 second time constant. > > John > > =A0This gave me a pretty noisy noise > > > > >signal. =A0(I didn't want to wait around for a longer TC. =A0I was the > >only one left 'at work' 5PM before the holiday.) =A0So I was only > >sensitive to excess noise at say the 10% -20% of thermal noise level. > >I changed the voltage from zero to 100mV to 1 volt and 8 volts. =A0And > >saw no increase in the noise. =A0When I disconected the input resistor > >the noise dropped by 1/2. =A0 I should try the same circiut with some > >carbon composite resistors! =A0Do they make those at 100 meg? > > >George H.- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -Oh, sorry. The nosie signals get amplified, filtered and then sent through a multiplier and low pass on the output. The final low pass was set at 1 second. With a noise signals at only ~600Hz, it's like doing 600 separtae measurments in one second... the noise in the noise is then sqrt(600)/600. 10-20% or so. George H.
Reply by ●December 24, 20102010-12-24
On Fri, 24 Dec 2010 08:27:27 -0800 (PST), George Herold <gherold@teachspin.com> wrote:>On Dec 23, 11:50�pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Thu, 23 Dec 2010 19:16:42 -0800 (PST), George Herold >> >> >> >> >> >> <gher...@teachspin.com> wrote: >> >On Dec 23, 8:48 pm, John Larkin >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> On Thu, 23 Dec 2010 15:41:49 -0800, Joerg <inva...@invalid.invalid> >> >> wrote: >> >> >> >John Larkin 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. >> >> >> >Actually, there is: >> >> >> >http://qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf >> >> >http://www.lorentz.leidenuniv.nl/beenakkr/mesoscopics/topics/noise/no... >> >> >> Well, that's just about metallic conductors. Nobody much talks about >> >> other stuff. >> >> >> But 0.1 mm isn't all that small a distance. Resistors inside ICs can >> >> be smaller than that. >> >> >> John- Hide quoted text - >> >> >> - Show quoted text - >> >> >Yeah, but what's important (as I read it) is the ratio of scattering >> >length to resistor length. �It's not easy to see the shot noise >> >signals in normal resistors. >> >> >I tried to measure excess noise in 100 meg resistors at the end of the >> >day today. �I failed. �It might be a circuit mistake. � I had a low >> >noise power supply feeding a 100meg thick film with the other end into >> >a TIA opamp. (Fet, opa134). �The feed back resistor was another 100meg >> >resistor. �The circuit had an RC corner at about 600Hz. �I set the >> >output time constant at 1 second. >> >> I don't understand that part, the 1 second time constant. >> >> John >> >> �This gave me a pretty noisy noise >> >> >> >> >signal. �(I didn't want to wait around for a longer TC. �I was the >> >only one left 'at work' 5PM before the holiday.) �So I was only >> >sensitive to excess noise at say the 10% -20% of thermal noise level. >> >I changed the voltage from zero to 100mV to 1 volt and 8 volts. �And >> >saw no increase in the noise. �When I disconected the input resistor >> >the noise dropped by 1/2. � I should try the same circiut with some >> >carbon composite resistors! �Do they make those at 100 meg? >> >> >George H.- Hide quoted text - >> >> - Show quoted text -- Hide quoted text - >> >> - Show quoted text - > >Oh, sorry. The nosie signals get amplified, filtered and then sent >through a multiplier and low pass on the output. The final low pass >was set at 1 second. With a noise signals at only ~600Hz, it's like >doing 600 separtae measurments in one second... the noise in the noise >is then sqrt(600)/600. 10-20% or so. > >George H.You could just dump the TIA output into a scope. Most scopes will calculate RMS these days. We did a similar thing a couple of months ago, with everything in a cookie can for shielding. We found a huge difference between metal film and cermet resistors, in the 50Mohm ballpark with 10 volts across the resistor. Our measurement bandwidth was also low, 1 KHz roughly, so we were probably seeing 1/f and other junk noise in the cermet. We didn't do spectral analysis, so I didn't know if there was shot noise, or if we could have resolved it in that bandwidth. I wish we'd have taken more data, because I need it now! Hey, I just had one of those duh! insights. All sorts of transducers could be connected to one another: accelerometers, microphones, antennas*, photodetectors, whatever. If each is at some temperature, say 20C, it generates noise from various mechanisms: brownian motion, local IR radiation, whatever. Any of them can be connected to a resistor, or to one another, and exchange power. If they are all at the same temperature, they must exchange equal amounts of power, or else conservation of energy is violated. So all transducers, and all resistors, and all antennas, must generate the same power at 20C. I suppose everybody but me knew this already. I've been seeing a lot of very silly "energy harvesting" things lately, like vibrating ribbons in moving air wiggling magnets near coils, 12" diameter windmills, peltiers in a car muffler, or piezo things in your running shoes that charge your iPod. Popular Mechanics has crazy ones on a regular basis, as does the press release mill at MIT. My invention, which I hereby donate to the world, is a wind chime surrounded by microphones. John * the antenna must be in a box at 20C, of course. An antenna pointed at the sky can act like a cold resistor, so you can derive free power from the difference in Johnson noise between a resistor at ambient and an antenna.
Reply by ●December 24, 20102010-12-24
John Larkin wrote:> On Thu, 23 Dec 2010 15:41:49 -0800, Joerg <invalid@invalid.invalid> > wrote: > >> John Larkin wrote: >>> 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. >>> >>> 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. >>> >> Actually, there is: >> >> http://qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf >> http://www.lorentz.leidenuniv.nl/beenakkr/mesoscopics/topics/noise/noise.html >> > > Well, that's just about metallic conductors. Nobody much talks about > other stuff. >Well, a contemporary resistor _is_ a metallic conductor. Very flat and thin metal :-) [...] -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Reply by ●December 24, 20102010-12-24
On Fri, 24 Dec 2010 10:04:07 -0800, Joerg <invalid@invalid.invalid> wrote:>John Larkin wrote: >> On Thu, 23 Dec 2010 15:41:49 -0800, Joerg <invalid@invalid.invalid> >> wrote: >> >>> John Larkin wrote: >>>> 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. >>>> >>>> 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. >>>> >>> Actually, there is: >>> >>> http://qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf >>> http://www.lorentz.leidenuniv.nl/beenakkr/mesoscopics/topics/noise/noise.html >>> >> >> Well, that's just about metallic conductors. Nobody much talks about >> other stuff. >> > >Well, a contemporary resistor _is_ a metallic conductor. Very flat and >thin metal :-) >Unless it's cermet or silicon or polysilicon or carbon film or tantalum nitride. I have no idea whether the anti-shot mechanisms work in them. John
Reply by ●December 24, 20102010-12-24
On Dec 24, 12:26=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Fri, 24 Dec 2010 08:27:27 -0800 (PST), George Herold > > > > > > <gher...@teachspin.com> wrote: > >On Dec 23, 11:50 pm, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Thu, 23 Dec 2010 19:16:42 -0800 (PST), George Herold > > >> <gher...@teachspin.com> wrote: > >> >On Dec 23, 8:48 pm, John Larkin > >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> >> On Thu, 23 Dec 2010 15:41:49 -0800, Joerg <inva...@invalid.invalid> > >> >> wrote: > > >> >> >John Larkin 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 bett=er 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 extr=a> >> >> >>> noise term that is proportional to the current (voltage/R)... b=ut 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 hav=e 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 manufacture=rs> >> >> >> don't know much about the subject, either. > > >> >> >Actually, there is: > > >> >> >http://qulab.eng.yale.edu/documents/reprints/PRL_shotnoise.pdf > >> >> >http://www.lorentz.leidenuniv.nl/beenakkr/mesoscopics/topics/noise=/no...> > >> >> Well, that's just about metallic conductors. Nobody much talks abou=t> >> >> other stuff. > > >> >> But 0.1 mm isn't all that small a distance. Resistors inside ICs ca=n> >> >> be smaller than that. > > >> >> John- Hide quoted text - > > >> >> - Show quoted text - > > >> >Yeah, but what's important (as I read it) is the ratio of scattering > >> >length to resistor length. It's not easy to see the shot noise > >> >signals in normal resistors. > > >> >I tried to measure excess noise in 100 meg resistors at the end of th=e> >> >day today. I failed. It might be a circuit mistake. I had a low > >> >noise power supply feeding a 100meg thick film with the other end int=o> >> >a TIA opamp. (Fet, opa134). The feed back resistor was another 100meg > >> >resistor. The circuit had an RC corner at about 600Hz. I set the > >> >output time constant at 1 second. > > >> I don't understand that part, the 1 second time constant. > > >> John > > >> This gave me a pretty noisy noise > > >> >signal. (I didn't want to wait around for a longer TC. I was the > >> >only one left 'at work' 5PM before the holiday.) So I was only > >> >sensitive to excess noise at say the 10% -20% of thermal noise level. > >> >I changed the voltage from zero to 100mV to 1 volt and 8 volts. And > >> >saw no increase in the noise. When I disconected the input resistor > >> >the noise dropped by 1/2. I should try the same circiut with some > >> >carbon composite resistors! Do they make those at 100 meg? > > >> >George H.- Hide quoted text - > > >> - Show quoted text -- Hide quoted text - > > >> - Show quoted text - > > >Oh, sorry. =A0The nosie signals get amplified, filtered and then sent > >through a multiplier and low pass on the output. =A0The final low pass > >was set at 1 second. =A0With a noise signals at only ~600Hz, it's like > >doing 600 separtae measurments in one second... the noise in the noise > >is then sqrt(600)/600. =A010-20% or so. > > >George H. > > You could just dump the TIA output into a scope. Most scopes will > calculate RMS these days.Yeah I do that as a check sometimes. The resolution is poor on the scope.> > We did a similar thing a couple of months ago, with everything in a > cookie can for shielding. We found a huge difference between metal > film and cermet resistors, in the 50Mohm ballpark with 10 volts across > the resistor. Our measurement bandwidth was also low, 1 KHz roughly, > so we were probably seeing 1/f and other junk noise in the cermet. We > didn't do spectral analysis, so I didn't know if there was shot noise, > or if we could have resolved it in that bandwidth. I wish we'd have > taken more data, because I need it now!I think it might be easier (faster) to look at the voltage dependence rather than the spectrum. The cermets are the noisy ones? The only really noiser resistors I've found are the carbon composites. When ever I get back to work I could look a little closer.> > Hey, I just had one of those duh! insights. All sorts of transducers > could be connected to one another: accelerometers, microphones, > antennas*, photodetectors, whatever. If each is at some temperature, > say 20C, it generates noise from various mechanisms: brownian motion, > local IR radiation, whatever. Any of them can be connected to a > resistor, or to one another, and exchange power. If they are all at > the same temperature, they must exchange equal amounts of power, or > else conservation of energy is violated. So all transducers, and all > resistors, and all antennas, must generate the same power at 20C. I > suppose everybody but me knew this already.Yeah there's kT/2 of energy always floating around. I guess there's some thermal limit in all detectors, lots of times something else bites you first. Photodiodes don't seem to get that much better when cooled. I suppose there might be some dark current change with temperature.> > I've been seeing a lot of very silly "energy harvesting" things > lately, like vibrating ribbons in moving air wiggling magnets near > coils, 12" diameter windmills, peltiers in a car muffler, or piezo > things in your running shoes that charge your iPod. Popular Mechanics > has crazy ones on a regular basis, as does the press release mill at > MIT. My invention, which I hereby donate to the world, is a wind chime > surrounded by microphones.It is strange, but people want to feel they are doing something to conserve energy. The big savings are in having smaller cars and houses, or at least more efficient houses. I cry a little when I see big picture windows facing north. With all crazy energy harvesting devices you can ask of them one simple question. "Will they generate more energy during their lifetime than they cost in energy to make?" George H.> > John > > * the antenna must be in a box at 20C, of course. An antenna pointed > at the sky can act like a cold resistor, so you can derive free power > from the difference in Johnson noise between a resistor at ambient and > an antenna.- Hide quoted text - > > - Show quoted text -
