I'm wanting to simulate noise in a TIA. It will use a discrete jfet at the input, then opamps. Check me out on this, please: I assume the jfet models have built-in gate equivalent noise voltages and currents, somewhere in the model string. Also assume the the LTC opamp models include noise params. Ditto Johnson noise in all resistors. The LT Spice help pdf file says that... ".NOISE -- Perform a Noise Analysis This is a frequency domain analysis that computes the noise due to Johnson, shot and flicker noise. The output data is noise spectral density per unit square root bandwidth. " Do resistors have shot noise? What if I want them to? What if I don't? There doesn't seem to be a noise source as a component. I guess I could use a resistor Johnson noise, and buffer that with a VCVS or VCCS as needed. Any other advice? John
noise in LT Spice
Started by ●December 21, 2010
Reply by ●December 21, 20102010-12-21
Reply by ●December 22, 20102010-12-22
>"John Larkin" wrote in message >news:75d2h613cdof17gkfsqpmhqnn9nhkt0vb0@4ax.com...>OK: LT Spice resistors seem to not have shot noise.>JohnProbably because resistors don't have shot noise! 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. Kevin Aylward B.Sc. www.kevinaylward.co.uk
Reply by ●December 22, 20102010-12-22
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! > >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. > >Kevin Aylward B.Sc. >www.kevinaylward.co.ukIf John Larkin says resistors have shot noise... they must ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●December 22, 20102010-12-22
Kevin Aylward 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! >Well, some of the resistors in this guy's TV probably do now: http://www.thesmokinggun.com/documents/bizarre/man-shoots-tv-over-bristol-palin-dancing -- SCNR, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Reply by ●December 22, 20102010-12-22
On Dec 21, 6:14=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> OK: LT Spice resistors seem to not have shot noise. > > JohnYup, 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.
Reply by ●December 22, 20102010-12-22
Kevin Aylward a �crit :>> "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! > > 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. >Not only DC current, but also AC... 1/f noise comes from random resistor changes, which also has impact on AC current. But instead of generating 1/f noise, it generates 1/f sidebands around your AC spectrum line... -- Thanks, Fred.
Reply by ●December 22, 20102010-12-22
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.>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. I could fake some noise current to simulate my resistor shot noise, and even make it adaptive to realtime current with a multiply somewhere. John
Reply by ●December 22, 20102010-12-22
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. We're buying some Dale RN55 metal films now, 50 megohms, and they're great. But the leadtime is 10-12 weeks, and they are something like $3.50 each. John
Reply by ●December 23, 20102010-12-23
On Dec 22, 7:45=A0pm, 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. =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(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. How do you distinguish shot noise from 1/f noise in high meg thick films? 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. George H.> > We're buying some Dale RN55 metal films now, 50 megohms, and they're > great. But the leadtime is 10-12 weeks, and they are something like > $3.50 each. > > John- Hide quoted text - > > - Show quoted text -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.
