George Herold wrote:> On Dec 24, 12:26 pm, John Larkin > <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:[...]>> 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. ...No wonder if even the big brass doesn't get it. Crystal-clear proof: This year we installed an evaporative cooler. It uses 0.4kW versus the 7kW the big central A/C guzzles. So I called the utility because I didn't see those coolers on the list of rebate-elegible upgrades. "No, there is no rebate for those" I was told. Yet there is a rebate for a higher SEER-number A/C. Which then probably consumes "only" 6kW. Great. <applause>> ... I cry a little when I see big picture windows facing north. >Or facing south in the summer. Or people setting the thermostat for the central heat/cooling unit at 70F and then leaving the sliding door open. [...] -- 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 25, 20102010-12-25
Reply by ●December 25, 20102010-12-25
John Larkin wrote:> 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.Provided they're in thermal equilibrium. Once you turn on the power, all bets are off. That's why you can get 25 kelvin T_noise amplifiers that work at room 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.Sorry, General Dynamics patented it already. ;) There are genuinely useful applications for energy harvesting...a customer of mine wants to generate power from the temperature gradient across the thickness of a soldier's T-shirt. The idea is to emit a TX pulse periodically as long as the temperature gradient is still there...if you get my drift. :( Cheers Phil Hobbs
Reply by ●December 30, 20102010-12-30
On Dec 24, 10:41=A0pm, George Herold <gher...@teachspin.com> wrote:> 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.invali=d>> > >> >> 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 be=tter is> > >> >> >>> to say greatly reduced.) If you've got some very big resistor=s in the> > >> >> >>> TIA then it might be possible for the RC corner to be below t=he 1/f> > >> >> >>> noise corner. This might sorta look like shot noise.... an ex=tra> > >> >> >>> 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 th=e noise> > >> >> >>> in big resistors... say 100 Meg and greater) > > > >> >> >>> George H. > > > >> >> >> We tested a lot of high-ohm resistors, and the thickfilms do h=ave shot> > >> >> >> noise. But the resistor I'm dealing with now is a liquid, ioni=c> > >> >> >> conduction, and according to the literature, they have full sh=ot> > >> >> >> noise. > > > >> >> >> There's something special about metals that smooths out electr=on flow.> > >> >> >> There's not a lot available online about shot noise in various > > >> >> >> resistor elements, and most of the high-ohm resistor manufactu=rers> > >> >> >> 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/noi=se/no...> > > >> >> Well, that's just about metallic conductors. Nobody much talks ab=out> > >> >> 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 scatterin=g> > >> >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 i=nto> > >> >a TIA opamp. (Fet, opa134). The feed back resistor was another 100m=eg> > >> >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 leve=l.> > >> >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. =A0The 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. =A0The cermets are the noisy ones? =A0The only > really noiser resistors I've found are the carbon composites. =A0 When > ever I get back to work I could look a little closer. > ><Snip other stuff.> I was looking at the escess noise of high meg resistors today. I could just barely see some at the highest bias voltage levels. (10 volts.) There was no way I could look at the voltage dependence of the excess noise. So I put a 10k ohm carbon comp resistor into the circuit. Here's the noise as a function of the bias voltage. http://img706.imageshack.us/i/10kexcess1.png/ The zero bias Johnson noise is 0.67 on the vertical. The bandwidth of the measurment was from 10 Hz to 1k Hz. It was hard to see if this was linear or quadratic in the bias voltage so I plotted the noise density divided by the bias voltage. Shown here, http://img510.imageshack.us/i/10kexcess2.png/ So at low bias it looks quadratic, but then rolls-off at higher voltages. Strange. George H.
Reply by ●December 30, 20102010-12-30
On Dec 30, 3:19=A0pm, George Herold <gher...@teachspin.com> wrote:> On Dec 24, 10:41=A0pm, George Herold <gher...@teachspin.com> wrote: > > > > > 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.inva=lid>> > > >> >> 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 resist=ors 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 noi=se. (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, io=nic> > > >> >> >> conduction, and according to the literature, they have full =shot> > > >> >> >> noise. > > > > >> >> >> There's something special about metals that smooths out elec=tron flow.> > > >> >> >> There's not a lot available online about shot noise in vario=us> > > >> >> >> resistor elements, and most of the high-ohm resistor manufac=turers> > > >> >> >> 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/n=oise/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 IC=s 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 scatter=ing> > > >> >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 o=f 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 10=0meg> > > >> >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 le=vel.> > > >> >I changed the voltage from zero to 100mV to 1 volt and 8 volts. A=nd> > > >> >saw no increase in the noise. When I disconected the input resist=or> > > >> >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 sen=t> > > >through a multiplier and low pass on the output. =A0The final low pa=ss> > > >was set at 1 second. =A0With a noise signals at only ~600Hz, it's li=ke> > > >doing 600 separtae measurments in one second... the noise in the noi=se> > > >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. =A0The 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 acros=s> > > 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. =A0The cermets are the noisy ones? =A0The onl=y> > really noiser resistors I've found are the carbon composites. =A0 When > > ever I get back to work I could look a little closer. > > <Snip other stuff.> > > I was looking at the escess noise of high meg resistors today. =A0I > could just barely see some at the highest bias voltage levels. =A0(10 > volts.) =A0There was no way I could look at the voltage dependence of > the excess noise. =A0So I put a 10k ohm carbon comp resistor into the > circuit. =A0Here's the noise as a function of the bias voltage. > > http://img706.imageshack.us/i/10kexcess1.png/ > > The zero bias Johnson noise is 0.67 on the vertical. =A0The bandwidth of > the measurment was from 10 Hz to 1k Hz. > > It was hard to see if this was linear or quadratic in the bias voltage > so I plotted the noise density divided by the bias voltage. =A0Shown > here, > > http://img510.imageshack.us/i/10kexcess2.png/ > > So at low bias it looks quadratic, but then rolls-off at higher > voltages. =A0Strange. > > George H.- Hide quoted text > > - Show quoted text -Hey doesn't anyone like my data? I should add that it's 'noisier' than it could be. At some point during the data taking the resistor started randomly 'switching' between two 'noise states'. The average noise would all of sudden more than double, and then after a while, (0.1 to ~100 seconds) switch back. It took me a while to notice this.... at the end of the day I set my DSO at 50sec/div and the output TC at 0.1sec, let it run at a constant 4 V bias, and looked over my shoulder every once in a while.... clear steps between two 'states'.
Reply by ●May 5, 20112011-05-05
>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 with both shot noise and Johnson noise. The current noise density will be: In^2 = 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 = 4.k.T/R + q.I Repeat this N times, and you have: In^2 = 4.k.T/R + 2.q.I/N So... even if a miniscule element of the resistor does exhibit shot 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 you want the noise to stay constant as you change temperature. It's also inconvenient if you want the noise to relate to a circuit current as in shot noise. It's rare that I would want to include external shot noise in a circuit simulation, but it could happen (e.g. if you have a sensor that isn't supported in your version of SPICE). Here is one of many possible ways to introduce the shot noise: You can use an idealised bipolar transistor, drive the circuit current 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. 1/1000). The output current of the CCCS is the same as the circuit current, but with shot noise (plus a fraction) added. --------------------------------------- Posted through http://www.Electronics-Related.com
Reply by ●May 5, 20112011-05-05
On May 5, 3:33=A0pm, "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 with bo=th> 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/NThat's pretty neat George! (Though I have to work through the details.) I think you might have to be a little careful how you split the current in each branch though. You can't have 1/2 an electron going one way and the other half going the other. Have you read Rolf Landauer on shot noise? He shows the shot noise in a resistor is reduced by the ratio of the scattering length to the resistor length... George H.> > So... =A0even if a miniscule element of the resistor does exhibit shot no=ise,> 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. > > =A0I sometimes do that, but you need to add temperature parameters if you > want the noise to stay constant as you change temperature. =A0It's also > inconvenient if you want the noise to relate to a circuit current as in > shot noise. =A0 > =A0It's rare that I would want to include external shot noise in a circui=t> 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: > =A0 You can use an idealised bipolar transistor, drive the circuit curren=t> 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. 1/1000)=.> The output current of the CCCS is the same as the circuit current, but wi=th> shot noise (plus a fraction) added. > > --------------------------------------- =A0 =A0 =A0 =A0 > Posted throughhttp://www.Electronics-Related.com
Reply by ●May 5, 20112011-05-05
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 with both >shot noise and Johnson noise. The current noise density will be: >In^2 = 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 = 4.k.T/R + q.I >Repeat this N times, and you have: >In^2 = 4.k.T/R + 2.q.I/N > >So... even if a miniscule element of the resistor does exhibit shot 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 you >want the noise to stay constant as you change temperature. It's also >inconvenient if you want the noise to relate to a circuit current as in >shot noise. > It's rare that I would want to include external shot noise in a circuit >simulation, but it could happen (e.g. if you have a sensor that isn't >supported in your version of SPICE). Here is one of many possible ways to >introduce the shot noise: > You can use an idealised bipolar transistor, drive the circuit current >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. 1/1000). >The output current of the CCCS is the same as the circuit current, but with >shot noise (plus a fraction) added. > > >Photodiodes have shot noise. Liquid (ionic conduction) resistors have shot noise. Very small resistors have shot noise. Semiconductor resistors, ditto. The reason metallic resistors don't have shot noise is a macro-scale interaction of electrons which smooths out the electron flow. Small resistors, where the e-e interactions don't have time to work, have shot noise. High-ohm cermet resistors have shot noise. We've measured it. And it's hard to find 50M metal-film resistors. John
Reply by ●May 5, 20112011-05-05
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 with b=oth> >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 > > >So... =A0even if a miniscule element of the resistor does exhibit shot n=oise,> >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 you > >want the noise to stay constant as you change temperature. =A0It's also > >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 circuit > >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 way=s to> >introduce the shot noise: > > =A0You can use an idealised bipolar transistor, drive the circuit curre=nt> >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. 1/1000=).> >The output current of the CCCS is the same as the circuit current, but w=ith> >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? (You'd need some 'squishy' metal box.... or a shielded room.) It should go as the scattering length, what's the scattering length of ions in liquids? George H. Very small resistors have shot noise. Semiconductor> resistors, ditto. > > The reason metallic resistors don't have shot noise is a macro-scale > interaction of electrons which smooths out the electron flow. Small > resistors, where the e-e interactions don't have time to work, have > shot noise. > > High-ohm cermet resistors have shot noise. We've measured it. And it's > hard to find 50M metal-film resistors. > > John- Hide quoted text - > > - Show quoted text -
Reply by ●May 5, 20112011-05-05
"George Storm"> > >Do resistors have shot noise? > > Resistors don't have shot noise (whatever they may be made of)** Wot bollocks.> Try the following thought experiment: take a hypothetial resistor with > both > shot noise and Johnson noise. The current noise density will be: > In^2 = 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 = 4.k.T/R + q.I > Repeat this N times, and you have: > In^2 = 4.k.T/R + 2.q.I/N > > So... even if a miniscule element of the resistor does exhibit shot > noise, > the resistor as a whole does not.** What a pile of mind numbing sophistry. Bet this fool has made similar estimates of how many angels can dance on the head of a pin. .... Phil
Reply by ●May 6, 20112011-05-06
On Thu, 5 May 2011 17:26:58 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On May 5, 4:14�pm, 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 with both >> >shot noise and Johnson noise. �The current noise density will be: >> >In^2 = 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 = 4.k.T/R + q.I >> >Repeat this N times, and you have: >> >In^2 = 4.k.T/R + 2.q.I/NDoesn'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... �even if a miniscule element of the resistor does exhibit shot 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 you >> >want the noise to stay constant as you change temperature. �It's also >> >inconvenient if you want the noise to relate to a circuit current as in >> >shot noise. � >> > It's rare that I would want to include external shot noise in a circuit >> >simulation, but it could happen (e.g. if you have a sensor that isn't >> >supported in your version of SPICE). �Here is one of many possible ways to >> >introduce the shot noise: >> > �You can use an idealised bipolar transistor, drive the circuit current >> >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. 1/1000). >> >The output current of the CCCS is the same as the circuit current, but 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? (You'd need some 'squishy' >metal box.... >or a shielded room.) It 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. John
