On Sat, 09 Apr 2022 20:55:53 -0400, time-nuts-requ...@lists.febo.com wrote: time-nuts Digest, Vol 216, Issue 16
Answers interspersed below. > ------------------------------ Message: 2 Date: Sat, 9 Apr 2022 13:38:58 +0200 From: "use...@teply.info" <use...@teply.info> Subject: [time-nuts] Re: +1/f of transistors To: time-nuts@lists.febo.com On 07.04.22 22:58, Joseph Gwinn wrote: >>>> What those folk are currently using for capacitance multipliers and the like (where low 1/f noise is also essential) are SiGe transistors like the following: BFP640H (Infineon), BFP780, SAV541 (MiniCircuits), and 2S2114K (NPN, beta 1200) for high current >>> and 2SD2704 from ROHM, even more beta >> Interesting. I would not have thought of this one. It's big and slow, and made from modern very clean silicon, so it could have low 1/f noise. Its transition frequency (*= gain-BW product?) is 35 MHz, so it ought to work on switcher noise. >>> Those SiGe transistors have wonderful low Rbb of just a few Ohms, which results in nice low voltage noise, but some have 1/f corners of 50 MHz or more; that kills my application completely. >> While these chips are small, they are made from very clean material, so one wonders why so high. The circuit should be physically designed as if it were to be handling GHz signals, because it could be oscillating far above the capability of available instruments to detect. > IF the base and emitter doping would be done through ion implantation, this can create a lot of defects, which act as recombination centres. .... I always wondered about such details. I gather from this and some following posts that it is known how to greatly reduce 1/f noise in transistors, but it's a nuisance, and so isn't generally done. But what saves us is if the intended purpose of the transistor type requires the cleanest of material and the best processes to yield low defects such as trapping centers. Such as the above-mentioned difficulties in getting the in-situ doping correct in SiGe transistors. I wonder if there would be a market for making selected standard transistors using a really good modern process, one that is otherwise overkill. The wafer need not be all of one kind of transistor. > ------------------------------ Message: 4 Date: Sat, 9 Apr 2022 06:31:27 -0700 From: "Richard (Rick) Karlquist" <rich...@karlquist.com> Subject: [time-nuts] Re: +1/f of transistors To: Discussion of precise time and frequency measurement <time-nuts@lists.febo.com>, "use...@teply.info" <use...@teply.info> I am seeing a lot of unsupported "theories" about what should be done to make devices with low 1/f noise. .... Hmm. What do you make of Handel's quantum theory of flicker noise? Van Der Ziel did support it, saying that while he (Ziel) didn't know if the derivation of the theory was correct, he _did_ know that this theory fit all the data he had collected over the decades, and nothing else fit nearly so well. Meaning that this kind of fit may be a big clue, even if the present theory isn't airtight. This was forty years ago. I'd guess that some people may be using Handel's theory simply because of the agreement with all that data. If I recall, he did predict that 1/f noise is inversely proportional to active volume, which is certainly as long observed - thus the paralleling of multiple smaller transistors or other devices. .<https://en.wikipedia.org/wiki/Quantum_1/f_noise> > ------------------------------ MMessage: 10 Date: Sat, 9 Apr 2022 11:35:06 -0700 From: "Lux, Jim" <j...@luxfamily.com> Subject: [time-nuts] Re: +1/f of transistors To: time-nuts@lists.febo.com Message-ID: <4a430e68-7444-2021-2814-cf182d2dd...@luxfamily.com> Content-Type: text/plain; charset=UTF-8; format=flowed On 4/9/22 10:03 AM, use...@teply.info wrote: > This is very, very true. Some manufacturers get very low noise or very low leakage (or both), essentially by being "lucky". From what I've been told, there's no good models, nor predictions - so people share "lore" of "if you get these 2Nxxxx FETs from the mfr in England, they're really good" until they aren't. There isn't enough market for these, so I suspect research money to "solve the problem" isn't available. Like all those microwave MMICs with low noise, they worry about 100 MHz and up (if not 1GHz), they certainly don't worry (or control) for noise at 5 MHz, or where the 1/f knee is. So just because you got good results with a batch of them, the next batch might not. It's not even clear you could come up with a standardized test method, because the noise depends on a lot of other factors (drain current, for instance). I bet (hope?) it isn't quite that bad. But the fact that one cannot test and sort for 10-Hz flicker noise in three milliseconds would suffice. > ------------------------------ Message: 11 Date: Sat, 9 Apr 2022 12:28:28 -0700 From: Alex Pummer <a...@pcscons.com> Subject: [time-nuts] Re: +1/f of transistors To: time-nuts@lists.febo.com Message-ID: <6a425b3c-717a-01a1-889b-c43650db9...@pcscons.com> Content-Type: text/plain; charset=UTF-8; format=flowed Noise in Physical Systems Including 1,f Noise, Biological Systems and Membranes : 10th International Conference, August 21-25, 1989, Budapest, Hungary 1990 <https://www.google.com/books/edition/Noise_in_Physical_Systems/WyVbzgEACAAJ?hl=en> Another good source. But at 700 pages, could take a while. Were there any revelations? Joe Gwinn _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.