On Sat, 17 Feb 2018 12:39:03 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 02/17/2018 11:53 AM, Jim Thompson wrote: >> On Fri, 16 Feb 2018 22:22:41 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 02/16/2018 01:19 PM, Jim Thompson wrote: >> >> [snip] >>>> >>>> Oooooops! LTspice doesn't have a .OUT file!! Nor does it have a .NET >>>> file. Sonofa gun! >>> >>> It does have netfiles, and stuff you print gets put in the log file. >>> >> [snip] >> >> Can you show me how that works? I haven't been able to figure that >> out. > >View -> SPICE netlistOK. That works. But fails to show me the actual model used. Therein is the prevarication.> >> >> Maybe a *.asc example that prints out a noise report? > >http://ltwiki.org/index.php?title=MEASURE_Evaluate_User_Defined_Electrical_QuantitiesThat's _not_ an asc file. Why did you snip "Maybe a *.asc example that prints out a noise report?" from my post? .MEAS is as useless as tits on a boar hog. Are you going to manually measure each component individually... including all the device parameters to locate a critical noise source? Gimme a break... there can be hundreds. So LTspice _doesn't_ print out a noise report? And you can't provide an asc example that does?> >Cheers > >Phil Hobbs...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | It's what you learn, after you know it all, that counts.
BJT base current 1/f noise
Started by ●February 10, 2018
Reply by ●February 17, 20182018-02-17
Reply by ●February 17, 20182018-02-17
>>>>> >>>> Oooooops! LTspice doesn't have a .OUT file!! Nor does it have a .NET >>>> file. Sonofa gun! >>> >>> It does have netfiles, and stuff you print gets put in the log file. >>> >> [snip] >> >>> Can you show me how that works? I haven't been able to figure that >>> out. > >>View -> SPICE netlist>OK. That works. But fails to show me the actual model used. Therein >is the prevarication.>> >>> >>> Maybe a *.asc example that prints out a noise report? >> >>http://ltwiki.org/index.php?title=MEASURE_Evaluate_User_Defined_Electrical_Quantities>That's _not_ an asc file.So what?>Why did you snip "Maybe a *.asc example that prints out a noise >report?" from my post?>.MEAS is as useless as tits on a boar hog. Are you going to manually >measure each component individually... including all the device >parameters to locate a critical noise source? > Gimme a break... there can be hundreds.>So LTspice _doesn't_ print out a noise report? > And you can't providean asc exam I was trying to help out--if you're just looking for reasons to hate LTspice, please have at it on your own. I have no interest in such reports myself--the plot facility is good enough. Cheers Phil Hobbs
Reply by ●February 17, 20182018-02-17
On Sat, 17 Feb 2018 10:49:46 -0800 (PST), pcdhobbs@gmail.com wrote:>>>>>> >>>>> Oooooops! �LTspice doesn't have a .OUT file!! �Nor does it have a .NET >>>>> file. �Sonofa gun! >>>> >>>> It does have netfiles, and stuff you print gets put in the log file. >>>> >>> [snip] >>> >>>> Can you show me how that works? �I haven't been able to figure that >>>> out. >> >>>View -> SPICE netlist > >>OK. �That works. �But fails to show me the actual model used. �Therein >>is the prevarication. > >>> >>>> >>>> Maybe a *.asc example that prints out a noise report? >>> >>>http://ltwiki.org/index.php?title=MEASURE_Evaluate_User_Defined_Electrical_Quantities > >>That's _not_ an asc file. > >So what? > >>Why did you snip "Maybe a *.asc example that prints out a noise >>report?" from my post? > >>.MEAS is as useless as tits on a boar hog. �Are you going to manually >>measure each component individually... including all the device >>parameters to locate a critical noise source? >�Gimme a break... there can be hundreds. > >>So LTspice _doesn't_ print out a noise report? >�And you can't provide >an asc exam > >I was trying to help out--if you're just looking for reasons to hate LTspice, please have at it on your own.I'm just the administrator of the truth serum >:-}>I have no interest in such reports myself--the plot facility is good enough.Glad you're a happy camper. Without a noise report (device-level) optimizing an amplifier would be a bitch.> >Cheers > >Phil Hobbs...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | It's what you learn, after you know it all, that counts.
Reply by ●February 17, 20182018-02-17
"Phil Hobbs" wrote in message news:2410c213-fba1-7e1e-6849-233c47a05d55@electrooptical.net... On 02/17/2018 10:31 AM, Kevin Aylward wrote:> "Gerhard Hoffmann" wrote in message > news:feqqa1F21heU1@mid.individual.net... > > Am 17.02.2018 um 09:21 schrieb Kevin Aylward: >> -----Original Message----- From: Jim Thompson > >>>> I have a noise report in SS where I order the noise of each >>>> component and >>>> state its % to the total. >> > >> In LTspice just plot onoise(R1) / gain to get it scaled to the input > > > Missed the point. > > I said an *ordered* *list*, for example > > Component Noise Report at Frequency = 10Hz > > "Rank" "Ref Des" "Noise (V/sqrtHz)" "Contribution" > > 1 qn1 1.80771u 63.7807 % > 2 qn1_1f 1.80249u 63.096 % > 3 qn2 485.026n 3.1778 % > 4 qn2_1f 434.741n 2.54486 % > 5 r3 341.859n 1.56584 % > 6 qn4 328.451n 1.44454 % > 7 qn4_1f 248.531n 824.51m % > 8 qn2_rb 201.111n 539.12m % > 9 qn4_rb 200.766n 537.269m % > 10 qn3 182.546n 443.968m % > 11 qn3_1f 161.473n 347.213m % > 12 qn1_ib 104.411n 145.027m % > 13 qn3_rb 76.5087n 77.8453m % > 14 qn1_rb 76.4419n 77.7093m % > 15 qn4_ic 73.1846n 71.2255m % > 16 qn2_ic 70.1976n 65.5281m % > 17 qn1_ic 45.3065n 27.2912m % > 18 qn3_ic 35.6833n 16.928m % > 19 qn2_ib 25.1827n 8.43072m % > 20 qn2_re 15.5829n 3.22808m % > 21 qn4_re 15.5567n 3.21723m % > 22 qn4_ib 14.3964n 2.75519m % > 23 qn3_ib 9.35346n 1.16302m % > 24 r2 8.44238n 947.487u % > 25 qn3_re 5.92827n 467.194u % > 26 qn1_re 5.92339n 466.425u % > 27 r4 3.89178n 201.344u % > 28 r5 1.86634n 46.3044u % > 29 r1 286.521p 1.09132u % > 30 qn4_rc 9.83235p 1.28516n % > 31 qn2_rc 8.91246p 1.05593n % > 32 qn1_rc 4.05183p 218.248p % > 33 qn3_rc 3.51699p 164.435p % > > Total Output Noise 1.93939u >>Does it work for subcircuits? One irritation in LTspice is that you >can't readily plot the noise contribution of op amps or even of >transistors if their models include parasitics (and so have to be >subcircuits).Yes. A typical opamp circuit will get you : Component Noise Report at Frequency = 10Hz "Rank" "Ref Des" "Noise (V/sqrtHz)" "Contribution" 1 r2 40.7136n 31.4283 % 2 r:X1:c2 20.8671n 7.2192 % 3 r:X1:c1 20.8671n 7.2192 % 4 q:X1:1 14.7515n 3.5402 % 5 q:X1:1_ic 14.7353n 3.53227 % 6 q:X1:2 14.7277n 3.52854 % 7 q:X1:2_ic 14.7277n 3.52854 % 8 r1 12.8748n 2.68501 % 9 q:X1:1_ib 692.029p 7.65353m % 10 r:X1:e1 104.023p 172.923u % 11 r:X1:e2 104.023p 172.923u % 12 d:X1:ln_id 6.15178p 604.782n % 13 d:X1:ln 6.15178p 604.782n % 14 d:X1:lp_id 6.15178p 604.781n % 15 d:X1:lp 6.15178p 604.781n % 16 d:X1:e_id 2.39867p 91.947n % 17 d:X1:e 2.39867p 91.947n % 18 d:X1:c_id 2.39857p 91.9395n % 19 d:X1:c 2.39857p 91.9395n % 20 r:X1:2 728.675f 8.48526n % 21 r:X1:ee 85.7994f 117.65p % 22 q:X1:2_ib 46.2129f 34.1283p % 23 r:X1:o1 14.4329f 3.33067p % 24 r:X1:o2 4.72999f 355.271f % The ordered list is really useful in knowing where the main problems are. Note that there is an option to chose what frequency that the order is done for. Someday I might rationalise the X naming convention, as it's shit as is. -- Kevin Aylward http://www.anasoft.co.uk - SuperSpice http://www.kevinaylward.co.uk/ee/index.html
Reply by ●February 18, 20182018-02-18
On 2/11/2018 5:33 PM, Phil Hobbs wrote:> On 02/11/2018 04:13 PM, John Larkin wrote: >> On Sun, 11 Feb 2018 15:44:14 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> On 02/11/2018 02:58 PM, John Larkin wrote: >>>> On Sun, 11 Feb 2018 13:17:25 -0500, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> On 02/11/2018 12:52 PM, John Larkin wrote: >>>>>> On Sun, 11 Feb 2018 12:32:55 -0500, Phil Hobbs >>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>> On 02/11/2018 11:34 AM, John Larkin wrote: >>>>>>>> On Sun, 11 Feb 2018 08:05:11 -0500, Phil Hobbs >>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>>>> On 02/10/2018 08:36 PM, John Larkin wrote: >>>>>>>>>> On Sat, 10 Feb 2018 19:39:32 -0500, Phil Hobbs >>>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>>>>>> On 02/10/18 18:41, John Larkin wrote: >>>>>>>>>>>> On Sat, 10 Feb 2018 17:18:55 -0500, Phil Hobbs >>>>>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> >>>>>>>>>>>> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> Is horrible. >>>>>>>>>>>>> >>>>>>>>>>>>> I'm just debugging a nice diode laser >>>>>>>>>>>>> controller for one customer and getting ready >>>>>>>>>>>>> to do another one for another (much better) >>>>>>>>>>>>> customer. It uses a ZXTP25020 PNP with a >>>>>>>>>>>>> biggish degeneration resistor and two-pole >>>>>>>>>>>>> bypassing of the base to get low noise at >>>>>>>>>>>>> high frequency. >>>>>>>>>>>>> >>>>>>>>>>>>> Turns out the 1/f noise is atrocious. The >>>>>>>>>>>>> total noise from 2 Hz on up is only a couple >>>>>>>>>>>>> of PPM, but it should be a factor of 10 >>>>>>>>>>>>> better than that. With a total base >>>>>>>>>>>>> resistance of 1k, the 1/f corner at 40 mA I_C >>>>>>>>>>>>> is over 10 kHz. >>>>>>>>>>>>> >>>>>>>>>>>>> The bias network looks like this: >>>>>>>>>>>>> >>>>>>>>>>>>> +9V 0----------*--------*-------* | | >>>>>>>>>>>>> | | | | | | R | 4.7 | >>>>>>>>>>>>> 3.3 R 39 ohm TF | nF | nF R CCC >>>>>>>>>>>>> CCC | CCC CCC | | | | / >>>>>>>>>>>>> | | |< ZXTP25020 From >>>>>>>>>>>>> 0--RRRR--*--RRRR--*---- | Op Amp >>>>>>>>>>>>> |\ 499 499 | \ | | --- \ / --> V >>>>>>>>>>>>> --> ----- | | GND >>>>>>>>>>>>> >>>>>>>>>>>>> The emitter resistor can drop up to about >>>>>>>>>>>>> 5V. >>>>>>>>>>>>> >>>>>>>>>>>>> I've got some higher-beta transistors on >>>>>>>>>>>>> order (FZT788B), and will reduce the >>>>>>>>>>>>> impedance of the bias network, but I was >>>>>>>>>>>>> fairly shocked that the 1/f noise was so >>>>>>>>>>>>> bad. >>>>>>>>>>>> >>>>>>>>>>>> That's a pretty fast transistor; could it be >>>>>>>>>>>> oscillating? >>>>>>>>>>> >>>>>>>>>>> Don't think so. I have a 1 GHz scope across the >>>>>>>>>>> laser, and didn't see anything like that, and >>>>>>>>>>> have applied thermal-digital analysis(*) to the >>>>>>>>>>> whole thing. I'll try going to 49.9 ohms and 47 >>>>>>>>>>> nF and see if it gets better, which it should. I >>>>>>>>>>> might need to use a TCA0372 booster to drive >>>>>>>>>>> 5-ohm resistors. :( >>>>>>>>>>> >>>>>>>>>>> Cheers >>>>>>>>>>> >>>>>>>>>>> Phil Hobbs >>>>>>>>>>> >>>>>>>>>>> (*) i.e. heat gun, cold spray, and fingers >>>>>>>>>> >>>>>>>>>> Yeah, the base current noise into the 1K resistor >>>>>>>>>> string could make a lot of noise... assuming the >>>>>>>>>> signal from the opamp is perfect. >>>>>>>>>> >>>>>>>>>> Is the overall feedback optical? >>>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>> Eventually, but at the moment it's coming from the >>>>>>>>> emitter resistor, so that the loop doesn't null out >>>>>>>>> the base current noise even within its bandwidth. >>>>>>>>> >>>>>>>>> The idea is to make the bias current way >>>>>>>>> sub-Poissonian, which if done right results in useful >>>>>>>>> amounts of amplitude squeezing of the light, i.e. >>>>>>>>> your detected photocurrent can actually be a few dB >>>>>>>>> quieter than full shot noise if you keep the optical >>>>>>>>> loss low enough. It's more of a checklist feature >>>>>>>>> for most uses, of course, but as you've pointed out >>>>>>>>> there are a lot of crappy diode laser controllers out >>>>>>>>> there, selling for cheap, so building one that just >>>>>>>>> makes the problems magically go away is attractive. >>>>>>>>> >>>>>>>>> Building a new-to-me kind of high dynamic range >>>>>>>>> system always seems to produce a bit of buried >>>>>>>>> treasure at first. The ZXTP25020 has super-low Rbb' >>>>>>>>> and Ree', so it would be an excellent candidate >>>>>>>>> except for the 1/f noise. If the higher-beta device >>>>>>>>> and lower drive impedance doesn't improve it enough, >>>>>>>>> I'll have to try Darlingtonizing it with one of >>>>>>>>> those nice SiGe:C devices to return the base current >>>>>>>>> to the collector circuit. >>>>>>>>> >>>>>>>>> That'd need a board spin though, and I'm super busy >>>>>>>>> at the moment. >>>>>>>> >>>>>>>> How about a Sziklai pair sort of thing, with a BF862 >>>>>>>> and a PNP? Or a Pfet-PNP darlington? Disappear the base >>>>>>>> current. >>>>>>> >>>>>>> I need it to be a PNP-type when it's done, because the >>>>>>> lasers are usually grounded-cathode. (Keeping the high >>>>>>> frequency output impedance high is the name of the >>>>>>> squeezing game--with an emitter follower you get twice >>>>>>> the shot noise.) If I could get good PFETs, that would >>>>>>> be great, but they're scarce these days and their noise >>>>>>> tends to be horrible. >>>>>>> >>>>>>> The Darlington-bandaid approach could be done with an NPN >>>>>>> and a couple of auxiliary current sources, but it would >>>>>>> be a bit of a mess. The advantage would be that (done >>>>>>> right) it would have the noise of the BFP640, which is >>>>>>> very low. >>>>>>> >>>>>>> Tomorrow I'll try reducing the base impedance by 10x and >>>>>>> see if that fixes it. Because of the 39-ohm emitter >>>>>>> resistor, it doesn't make sense to go very much lower >>>>>>> than that. >>>>>>> >>>>>>> One nice thing about 1/f noise is that a 10x amplitude >>>>>>> improvement gets you 100x lower corner frequency. At >>>>>>> that point I can put in a low-frequency bandaid if I need >>>>>>> to, such as sensing the voltage across the base resistor >>>>>>> and dumping the equivalent into the emitter so that the >>>>>>> op amp tracks out the LF noise. The trick will be to >>>>>>> avoid a noise peak at the crossover frequency of the >>>>>>> bandaid. >>>>>> >>>>>> Here's an idea that I've never actually built: >>>>>> >>>>>> https://www.dropbox.com/s/lr3aekzziecz7pz/Isrc_cascode_Ib.JPG?raw=1 >>>>>> >>>>>> I don't remember what those two caps are for. >>>>>> >>>>> Interesting. It has the current noise of the FET at low >>>>> frequency, though, and looks like it has full shot noise at >>>>> high frequency on account of the caps. >>>>> >>>>> I'd be looking at something vaguely of that kind for the >>>>> bandaid approach--next time I have a Saturday afternoon free >>>>> I'll have a whack at it. >>>> >>>> Have you considered a bootstrap current source? That solves a >>>> lot of problems. Adding an inductor somewhere makes it better >>>> at high frequencies, so you can concentrate on the low end. Any >>>> copper TC error is easily compensated. >>> >>> The bootstrap sources I know about use op amps to control things >>> at all frequencies, so they're at least 10-15 dB noisier at >>> medium-to-high frequency than a transistor with Rbb' of an ohm. >>> It's really just the 1/f noise that's the problem. An inductor >>> is a possibility, though--it might very well help up around f_T. >> >> Chopamp? > > The simple op amp + BJT + local feedback approach has really stellar > noise performance at high frequency. The issue at low frequency is > that the base current 1/f noise doesn't get tracked out by the op amp > loop because it appears in the collector circuit but not in the > emitter circuit, which is where the FB is applied. > > ISTM there are four ways of fixing this wart without degrading the HF > noise. From easiest to hardest: > > 1. Reduce the 1/f noise by reducing the base circuit impedance. > > 2. Do some Darlingtonish thing to return the base current to the > collector circuit without adding significant voltage noise. > > 3. Use some more complicated local feedback scheme to synthesize a > copy of the base current and stick it into the emitter circuit so > that the main loop tracks it out. > > 4. Come up with some completely new scheme. > > Because the laser current-tunes, its linewidth is degraded more by > strong low-frequency components than by the same noise power spread > out over the full bandwidth. (This is just like an FM transmitter.) > Thus it would be worth trading off a bit of HF noise to fix this > issue, but I'm greedy and want to have it all. ;) > > Chopamps tend to have low frequency noise around 20-30 nV in 1 Hz all > the way down to DC, which isn't bad at all--it would flatten out my > noise below about 20 Hz. My faves are the OPA2188, which is a 32V > dual, and the OPA378, which is a bit noisier in the flatband but > whose noise doesn't rise at all at low frequency, at least down to 10 > uHz (~1 cycle/day) which is as far as I've measured it. > > I'd be very interested to hear about yours and others' fave > chopamps--there's a depressing amount of specsmanship going on in > their datasheets.ADA4528: noise peak at 200 kHz but otherwise well behaved. 2.2-5.5V supply. I'm also using an LT6655-2.5 as a (DAC) reference - seems to have the similar no 1/f with a noise peak characteristic. 6-8 uF on the output flattens the noise nicely. -- Grizzly H.
Reply by ●February 18, 20182018-02-18
On Sunday, February 18, 2018 at 12:51:05 AM UTC+11, Gerhard Hoffmann wrote:> Am 17.02.2018 um 09:21 schrieb Kevin Aylward: > > -----Original Message----- From: Jim Thompson > > >>> I have a noise report in SS where I order the noise of each component > >>> and > >>> state its % to the total. > > > > In LTspice just plot onoise(R1) / gain to get it scaled to the input > > > > Oscillator phase noise is somewhat bizarre. It acts like FM capture > > effect. You can have a noise plot, find and eliminate a dominant noise > > noise, yet still have the "improved" topology have an essentially > > overlaid new phase plot. A new noise source just pops up as the > > dominant, and the noise don't change. > > Oscillator phase noise is not bizarre at all. It is just that Spice > cannot handle nonlinear noise analysis. Harmonic balance analysis > is missing. > > Spice calculates noise in the linearized circuit at the operating > point. But oscillators are inherently nonlinear since they need > a limiting mechanism or they would go super nova after some time. > (Or not oscillate at all.) > > During each part of the oscillation cycle the OP is different, > gain is different, contributions are different.That depends on the gain control mechanism. In general Wien bridge oscillators use gain control elements that are close to linear over the oscillation cycle. Jim Williams used a FET as his gain adjustment mechanism, and it's resistance would stay the same over the oscillation cycle, and you could change the resistance by changing the gate voltage (which was a lot bigger than the sinusoidal voltage at the FET, and you can AC-couple that sinusoidal voltage into the gate bias voltage if you are feeling perfectionist). http://cds.linear.com/docs/en/application-note/an43f.pdf see figure 45 on page 31. <snip> -- Bill Sloman, Sydney
Reply by ●February 18, 20182018-02-18
On 02/18/2018 12:10 AM, mixed nuts wrote:> On 2/11/2018 5:33 PM, Phil Hobbs wrote:>> I'd be very interested to hear about yours and others' fave >> chopamps--there's a depressing amount of specsmanship going on in >> their datasheets. > > ADA4528: noise peak at 200 kHz but otherwise well behaved. 2.2-5.5V supply. > > I'm also using an LT6655-2.5 as a (DAC) reference - seems to have the > similar no 1/f with a noise peak characteristic. 6-8 uF on the output > flattens the noise nicely. >Looks like an interesting reference. How low does that "no 1/f" behaviour go? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●February 18, 20182018-02-18
>wrote in message >news:e22a8b51-260a-4ca2-a035-a10b54cddaad@googlegroups.com...On Sunday, February 18, 2018 at 12:51:05 AM UTC+11, Gerhard Hoffmann wrote:> Am 17.02.2018 um 09:21 schrieb Kevin Aylward: > > -----Original Message----- From: Jim Thompson > > >>> I have a noise report in SS where I order the noise of each component > >>> and > >>> state its % to the total. > > > > In LTspice just plot onoise(R1) / gain to get it scaled to the input > > > > Oscillator phase noise is somewhat bizarre. It acts like FM capture > > effect. You can have a noise plot, find and eliminate a dominant noise > > noise, yet still have the "improved" topology have an essentially > > overlaid new phase plot. A new noise source just pops up as the > > dominant, and the noise don't change. > >> Oscillator phase noise is not bizarre at all. It is just that Spice >> cannot handle nonlinear noise analysis. Harmonic balance analysis >> is missing. > >> Spice calculates noise in the linearized circuit at the operating > >point. But oscillators are inherently nonlinear since they need > >a limiting mechanism or they would go super nova after some time. > >(Or not oscillate at all.) > >> During each part of the oscillation cycle the OP is different, >> gain is different, contributions are different.>That depends on the gain control mechanism.Nope. The gain control is not the only active device. For xtal oscillators, there is usually no specific gain limiter. There just limit by voltage or current starvation.> In general Wien bridge oscillators use gain control elements that are > close to linear over the oscillation cycle.>Jim Williams used a FET as his gain adjustment mechanism, and it's >resistance would stay the same over the oscillation cycle, and you could >change the resistance by changing the gate voltage >>(which was a lot bigger than the sinusoidal voltage at the FET, and you >>can AC-couple that sinusoidal voltage into the gate bias voltage if you >>are feeling perfectionist).I think you are missing the point. Its not just one device, say operating over an approximate constant resistance noise. All active devices are nonlinear. For example, consider a main amplifying transistor. Its collector current noise is sqrt(2.IC.q) and its base current noise sqrt(2.q.ib). This noise is changing over the whole cycle as the transistor goes from cutoff to full on. Phase noise tools determine the steady state solution i.e. the PSS Periodic Steady State, and use this solution to calculate the Phase Noise on a point by point bases over the the whole waveform. It matters. -- Kevin Aylward http://www.anasoft.co.uk - SuperSpice http://www.kevinaylward.co.uk/ee/index.html
Reply by ●February 18, 20182018-02-18
Am 17.02.2018 um 16:56 schrieb Phil Hobbs:> > Good oscillators generally have ALC, though, so the self-limiting > behaviour isn't such an issue with simulations (at least outside the ALC > bandwidth).No, not at all generally. It is easy to spoil a lot and the advantage is small in reality. But I do have a design that works well. cheers, Gerhard
Reply by ●February 18, 20182018-02-18
On 2/18/2018 1:15 PM, Phil Hobbs wrote:> On 02/18/2018 12:10 AM, mixed nuts wrote: >> On 2/11/2018 5:33 PM, Phil Hobbs wrote: > >>> I'd be very interested to hear about yours and others' fave >>> chopamps--there's a depressing amount of specsmanship going on in >>> their datasheets. >> >> ADA4528: noise peak at 200 kHz but otherwise well behaved. 2.2-5.5V >> supply. >> >> I'm also using an LT6655-2.5 as a (DAC) reference - seems to have the >> similar no 1/f with a noise peak characteristic. 6-8 uF on the output >> flattens the noise nicely. > > Looks like an interesting reference. How low does that "no 1/f" > behaviour go?Don't know for certain. I'm not tooled to measure it directly. It's all part of a control loop to stabilize a magnetic field to ~ 1 ppm (NMR magnetometer). Temperature is the primary driver but our oven wanders around about 0.1C which is also resolution of the system's temperature measurements. We can see doors opening and A/C cycling when the system is in the oven. The measured temps correlate with the correction currents within a ppm or two over hours so there's no evidence that the reference is worse than that. -- Grizzly H.
