Request for 1/f SPICE noise models for BJTs - Page 1
Forum section: electronics / projects

author: moffy
author_rank: Super Contributor
timestamp: June 27, 2023, 06:20:50 am
content: I would like to do some noise models with standard BJTs e.g. 2N2222a, BC547 etc., especially the 1/f noise but the AF and KF factors are missing from the models, e.g. LTSpice. Does anyone have such models? Thanks for your help, I am looking for a low noise common transistor, currently the 2N2222a is my choice.

author: magic
author_rank: Super Contributor
timestamp: June 27, 2023, 07:25:02 am
content: I'm afraid your best bet would be testing different transistors, perhaps directly in the circuit you want to use them with.Proper noise models are rare and certainly not included in LTspice out of the box.Performance of generic parts may vary from vendor to vendor.

author: moffy
author_rank: Super Contributor
timestamp: June 27, 2023, 08:12:31 am
content: Quote from: magic on June 27, 2023, 07:25:02 amI would have to build something specific which I am trying to avoid i.e. to measure 1/f noise, I would like to model first then build if possible. Vendor variations will happen but with the 2N2222A they do provide a series of NF graphs so I would hope for some consistency. Any help with the modelling appreciated.

author: moffy
author_rank: Super Contributor
timestamp: June 27, 2023, 12:20:39 pm
content: On the off chance that PSPICE in the Orcad trial might have some useful models I downloaded it and in the Infineon_s_afbjt.lib found that they have AF and KF figures, a lot of them are repetitive across different devices so I am not sure how reliable they are.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 27, 2023, 12:37:46 pm
content: Simulation might not help much with noise between different models. In practice the noise differs a lot even when comparing between the same type of transistors. I remember BC413 used to be a frequent choice for low noise in audio preamplifiers.

author: moffy
author_rank: Super Contributor
timestamp: June 27, 2023, 01:01:01 pm
content: Quote from: RoGeorge on June 27, 2023, 12:37:46 pmThanks for the recommendation, I've never heard of the BC413 before and the datasheet looks really old. I guess I am probably more interested in the noise current as that is where the 1/f noise is and broadband is largely determined by Rb, for 0 Rs, at least according to SPICE. I would still like to try reasonable sims in spite of the caveats.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: June 27, 2023, 01:52:02 pm
content: some interesting measurements:http://www.dicks-website.eu/low_noise_amp_part3/part3.html

author: moffy
author_rank: Super Contributor
timestamp: June 27, 2023, 02:01:38 pm
content: Quote from: doktor pyta on June 27, 2023, 01:52:02 pmThank you, yes they are very interesting, I had noticed it before, and it is real life noise results, the ZTX851-3 are very low noise. If only I had a spectrum analyser that went down to DC. Still I am not sure how to go from noise curves to AF and KF factors.

author: magic
author_rank: Super Contributor
timestamp: June 27, 2023, 02:08:43 pm
content: These measurements should be taken with a grain of salt at low frequencies because the 100μF base capacitor has meaningful reactance there. I think it's possible that the results would be different if it were increased.Horowitz&Hill used several mF in this position. Their test circuit is crazy complex, though.

author: mawyatt
author_rank: Super Contributor
timestamp: June 27, 2023, 02:23:55 pm
content: Creating a data sheet on BJT device characteristics is one thing, however the additional effort/cost to generate accurate BJT SPICE models is high, especially the complex models like HICUM or MEXTRAM, even VBIC.The only ones we're aware of are for specific foundry processes, like IBM SiGe BiCMOS processes, but certain that AD and TI also have such but all seem to be proprietary.The importance of well representing, accurate device models, especially for IC design, can't be overstated, but must fit the ROI $ supplier/foundry models also.If you find some accurate models for typical generic devices, please inform everyone, many times we've looked and come up short!!Best,

author: moffy
author_rank: Super Contributor
timestamp: June 27, 2023, 02:31:11 pm
content: Quote from: mawyatt on June 27, 2023, 02:23:55 pmI feel your frustration with this oversight even though I am interested in only a small aspect of the BJTs model. If I find anything reliable I will share it to aid any others who might find it useful.

author: magic
author_rank: Super Contributor
timestamp: June 27, 2023, 02:36:40 pm
content: For jellybeans, I recall seeing noise plots in some datasheets, I think it was ON semi. Noise density for a few selected values of source resistance and bias were included.Again, there is likely plenty of variation between vendors, parts from the '60s and from today, mystery meat transistors from China, etc.You will find more comprehensive information in some dedicated low noise transistors from the likes of Rohm or Toshiba.No one seems to bother publishing SPICE models.

author: moffy
author_rank: Super Contributor
timestamp: June 27, 2023, 02:45:17 pm
content: Quote from: magic on June 27, 2023, 02:36:40 pmI'll check out the suggested manufacturers see if I can find some nuggets.

author: David Hess
author_rank: Super Contributor
timestamp: June 27, 2023, 04:38:01 pm
content: Quote from: moffy on June 27, 2023, 01:01:01 pmRb (base spreading resistance) has a major effect on noise, and Rb and flicker noise vary significantly with structure, which leads to:Quote from: moffy on June 27, 2023, 02:01:38 pmSuper E-Line transistors like the ZTX851, and I think ring emitter or perforated emitter transistors, should have very low base spreading resistance and therefor low noise, and testing apparently confirms this.There are some monolithic integrated transistors like the MAT series and LM394 which also very low noise because of very low base spreading resistance, but here I think it is because they use an interdigitated design? I do not know about the matched transistors from THAT Corporation.

author: moffy
author_rank: Super Contributor
timestamp: June 27, 2023, 04:57:59 pm
content: Quote from: David Hess on June 27, 2023, 04:38:01 pmMaybe I should try and match the 1/f curve for the real life measurement of the ZTX851 mentioned by doktor pyta, will have a little think about it. I have some SSM2210s which are great for audio but lots of capacitance, limiting the BW as well as being very expensive and obsolete.

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: July 01, 2023, 06:53:46 pm
content: An interesting thread in this context:<https://www.diyaudio.com/community/threads/my-version-of-the-g-1000-low-noise-measurement-amp-for-ikoflexer.175044/page-30>cheers, Gerhard

author: moffy
author_rank: Super Contributor
timestamp: July 01, 2023, 10:00:27 pm
content: Quote from: Gerhard_dk4xp on July 01, 2023, 06:53:46 pmThanks for the link I will check it out.

author: moffy
author_rank: Super Contributor
timestamp: July 01, 2023, 10:10:13 pm
content: The link seems to reference a "Wurcer LNA" which led to here:https://www.diyaudio.com/community/threads/my-version-of-the-g-1000-low-noise-measurement-amp-for-ikoflexer.175044/and a curious looking design for N channel JFETs. I will have to study the post for a bit.

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: July 02, 2023, 04:32:11 am
content: Scott Wurcer is the designer of the AD797 e.a. AFAIK.Sad to see that he disabled his account.I learned a lot from him.Gerhard

author: mawyatt
author_rank: Super Contributor
timestamp: July 02, 2023, 03:24:37 pm
content: That seems correct, the AD797 is a brilliant Op-Amp concept (~ Patent 9136807), and after reading the informative notes and low noise preamp by AD Fellow Scott Wurcer in the mentioned low-noise measurement thread by moffy, not surprised. Seems he's from MIT and likely had Dr James Roberge as an adviser!Best,

author: moffy
author_rank: Super Contributor
timestamp: October 13, 2023, 05:47:27 am
content: This is probably superfluous as I imagine that you would all be following :https://www.eevblog.com/forum/projects/low-noise-0-01hz-1mhz-amplifier-project/but I promised mawyatt that I would post any good BJT spice models and 'magic' has pointed to the Toshiba models:https://toshiba.semicon-storage.com/ap-en/semiconductor/knowledge/highlighted-contents/articles/simulating-the-transient-characteristics-of-mosfet-more-accurately/simulating-the-transient-characteristics-of-mosfet-more-accurately-download.htmlFor any that missed that mention.P.S. The link is only for MOSFETs, not quite what I first thought.But their BJT models do have a non generic value for Rb!

author: magic
author_rank: Super Contributor
timestamp: October 13, 2023, 06:03:04 am
content: Sorry to disappoint, but I specifically wrote:Quote from: magic on October 13, 2023, 04:46:50 amThe flicker noise in that simulation over there came from the rest of the circuit.

author: moffy
author_rank: Super Contributor
timestamp: October 13, 2023, 06:07:11 am
content: Thanks for the clarification but the models could still be useful.

author: moffy
author_rank: Super Contributor
timestamp: October 14, 2023, 09:05:02 am
content: Just downloaded from NXP their SPICE models for the BFU5XX family and not only do they have Rb values but also Af and Kf (1/f noise) values. They can be found at:https://www.nxp.com/downloads/en/spice-model/BFU5XX_family_SPICE_GP_v2.zip